DTO Projections with Constructors

This recipe shows how to use [Expressive] constructors to project database rows directly into DTOs inside your LINQ queries -- with no boilerplate Select expressions and full SQL translation.

The Problem

Projecting entities into DTOs usually requires writing a Select expression that repeats the mapping logic:

// Repetitive -- mapping duplicated in every query
var customers = dbContext.Customers
    .Select(c => new CustomerDto
    {
        Id = c.Id,
        FullName = $"{c.FirstName} {c.LastName}",
        IsActive = c.IsActive,
        OrderCount = c.Orders.Count()
    })
    .ToList();

If the mapping changes you must update every Select that uses it.

The Solution: [Expressive] Constructor

Mark a constructor with [Expressive] and call it directly in your query. The source generator emits a MemberInit expression that EF Core translates to SQL:

C#

db
    .Customers
    .Where(c => c.Country != null)
    .Select(c => new CustomerDto(c))

// Setup
public class CustomerDto
{
    public int Id { get; set; }
    public string Name { get; set; } = "";
    public string? Country { get; set; }
    public int OrderCount { get; set; }

    public CustomerDto() { }

    [Expressive]
    public CustomerDto(Customer c)
    {
        Id = c.Id;
        Name = c.Name;
        Country = c.Country;
        OrderCount = c.Orders.Count();
    }
}

SELECT "c"."Id", "c"."Name", "c"."Country", (
    SELECT COUNT(*)
    FROM "Orders" AS "o"
    WHERE "c"."Id" = "o"."CustomerId") AS "OrderCount"
FROM "Customers" AS "c"
WHERE "c"."Country" IS NOT NULL

SELECT c."Id", c."Name", c."Country", (
    SELECT count(*)::int
    FROM "Orders" AS o
    WHERE c."Id" = o."CustomerId") AS "OrderCount"
FROM "Customers" AS c
WHERE c."Country" IS NOT NULL

SELECT [c].[Id], [c].[Name], [c].[Country], (
    SELECT COUNT(*)
    FROM [Orders] AS [o]
    WHERE [c].[Id] = [o].[CustomerId]) AS [OrderCount]
FROM [Customers] AS [c]
WHERE [c].[Country] IS NOT NULL

playground.customers.Aggregate([
    {
         "$match" : {
             "Country" : { "$ne" : null } 
        } 
    },
    {
         "$project" : {
             "_id" : "$_id",
            "Name" : "$Name",
            "Country" : "$Country",
            "OrderCount" : { "$size" : "$Orders" } 
        } 
    }
])

// === ExpressiveSharp_Docs_Playground_Snippet_CustomerDto._ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Customer.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Linq;
using System.Linq.Expressions;
using ExpressiveSharp;
using ExpressiveSharp.EntityFrameworkCore;
using ExpressiveSharp.Docs.PlaygroundModel.Webshop;
using ExpressiveSharp.Docs.Playground.Snippet;

namespace ExpressiveSharp.Generated
{
    static partial class ExpressiveSharp_Docs_Playground_Snippet_CustomerDto 
    {
        // [Expressive]
        // public CustomerDto(Customer c)
        // {
        //     Id = c.Id;
        //     Name = c.Name;
        //     Country = c.Country;
        //     OrderCount = c.Orders.Count();
        // }
        static global::System.Linq.Expressions.Expression<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer, global::ExpressiveSharp.Docs.Playground.Snippet.CustomerDto>> _ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Customer_Expression() 
        {
            var p_c = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer), "c");
            var expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.CustomerDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null));
            var expr_1 = global::System.Linq.Expressions.Expression.Property(p_c, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // c.Id
            var expr_2 = global::System.Linq.Expressions.Expression.Property(p_c, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer).GetProperty("Name", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // c.Name
            var expr_3 = global::System.Linq.Expressions.Expression.Property(p_c, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer).GetProperty("Country", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // c.Country
            var expr_5 = global::System.Linq.Expressions.Expression.Property(p_c, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer).GetProperty("Orders", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // c.Orders
            var expr_4 = global::System.Linq.Expressions.Expression.Call(global::System.Linq.Enumerable.First(global::System.Linq.Enumerable.Where(typeof(global::System.Linq.Enumerable).GetMethods(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static), m => m.Name == "Count" && m.IsGenericMethodDefinition && m.GetGenericArguments().Length == 1 && m.GetParameters().Length == 1 && m.GetParameters()[0].ParameterType.IsGenericType && !m.GetParameters()[0].ParameterType.IsGenericParameter)).MakeGenericMethod(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order)), new global::System.Linq.Expressions.Expression[] { expr_5 });
            var expr_6 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.CustomerDto).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_1);
            var expr_7 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.CustomerDto).GetProperty("Name", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_2);
            var expr_8 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.CustomerDto).GetProperty("Country", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_3);
            var expr_9 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.CustomerDto).GetProperty("OrderCount", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_4);
            var expr_10 = global::System.Linq.Expressions.Expression.MemberInit(expr_0, expr_6, expr_7, expr_8, expr_9);
            return global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer, global::ExpressiveSharp.Docs.Playground.Snippet.CustomerDto>>(expr_10, p_c);
        }
    }
}


// === ExpressiveSharp_Docs_Playground_Snippet_CustomerDto.Attributes.g.cs ===
// <auto-generated/>

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    static partial class ExpressiveSharp_Docs_Playground_Snippet_CustomerDto { }
}


// === ExpressionRegistry.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Reflection;

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    internal static class ExpressionRegistry
    {
        private static Dictionary<nint, LambdaExpression> Build()
        {
            const BindingFlags allFlags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static;
            var map = new Dictionary<nint, LambdaExpression>();
            
            Register(map, typeof(global::ExpressiveSharp.Docs.Playground.Snippet.CustomerDto).GetConstructor(allFlags, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer) }, null), "ExpressiveSharp.Generated.ExpressiveSharp_Docs_Playground_Snippet_CustomerDto", "_ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Customer_Expression");
            
            return map;
        }
        
        private static volatile Dictionary<nint, LambdaExpression> _map = Build();
        
        internal static void ResetMap() => _map = Build();
        
        public static LambdaExpression TryGet(MemberInfo member)
        {
            var handle = member switch
            {
                MethodInfo m      => (nint?)m.MethodHandle.Value,
                PropertyInfo p    => p.GetMethod?.MethodHandle.Value,
                ConstructorInfo c => (nint?)c.MethodHandle.Value,
                _                 => null
            };
            
            return handle.HasValue && _map.TryGetValue(handle.Value, out var expr) ? expr : null;
        }
        
        private static void Register(Dictionary<nint, LambdaExpression> map, MethodBase m, string exprClass, string exprMethodName)
        {
            if (m is null) return;
            var exprType = m.DeclaringType?.Assembly.GetType(exprClass) ?? typeof(ExpressionRegistry).Assembly.GetType(exprClass);
            var exprMethod = exprType?.GetMethod(exprMethodName, BindingFlags.Static | BindingFlags.NonPublic);
            if (exprMethod is null) return;
            var expr = (LambdaExpression)exprMethod.Invoke(null, null)!;
            
            // Apply declared transformers from the generated class (if any)
            const string expressionSuffix = "_Expression";
            if (exprMethodName.EndsWith(expressionSuffix, StringComparison.Ordinal))
            {
                var transformersSuffix = exprMethodName.Substring(0, exprMethodName.Length - expressionSuffix.Length) + "_Transformers";
                var transformersMethod = exprType.GetMethod(transformersSuffix, BindingFlags.Static | BindingFlags.NonPublic);
                if (transformersMethod?.Invoke(null, null) is global::ExpressiveSharp.IExpressionTreeTransformer[] transformers)
                {
                    Expression transformed = expr;
                    foreach (var t in transformers) transformed = t.Transform(transformed);
                    if (transformed is LambdaExpression lambdaResult) expr = lambdaResult;
                }
            }
            
            map[m.MethodHandle.Value] = expr;
        }
    }
}


// === PolyfillInterceptors_b1293e61.g.cs ===
// <auto-generated/>
#nullable disable

namespace ExpressiveSharp.Generated.Interceptors
{
    internal static partial class PolyfillInterceptors
    {
        [global::System.Runtime.CompilerServices.InterceptsLocationAttribute(1, "G8FTZQB0uOILx9INpC1Ka6oBAABfX1NuaXBwZXQuY3M=")]
        internal static global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.Playground.Snippet.CustomerDto> __Polyfill_Select_3e61_16_5(
            this global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer> source,
            global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer, global::ExpressiveSharp.Docs.Playground.Snippet.CustomerDto> __func)
        {
            // Source: c => new CustomerDto(c)
            var i3e6116c5_p_c = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer), "c");
            var i3e6116c5_expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.CustomerDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer) }, null), i3e6116c5_p_c); // new CustomerDto(c)
            var __lambda = global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer, global::ExpressiveSharp.Docs.Playground.Snippet.CustomerDto>>(i3e6116c5_expr_0, i3e6116c5_p_c);
            return global::ExpressiveSharp.ExpressiveQueryableExtensions.AsExpressive(
                global::System.Linq.Queryable.Select(
                    (global::System.Linq.IQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer>)source,
                    __lambda));
        }
        [global::System.Runtime.CompilerServices.InterceptsLocationAttribute(1, "G8FTZQB0uOILx9INpC1Ka4cBAABfX1NuaXBwZXQuY3M=")]
        internal static global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer> __Polyfill_Where_3e61_15_5(
            this global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer> source,
            global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer, bool> __func)
        {
            // Source: c => c.Country != null
            var i3e6115c5_p_c = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer), "c");
            var i3e6115c5_expr_1 = global::System.Linq.Expressions.Expression.Property(i3e6115c5_p_c, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer).GetProperty("Country", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // c.Country
            var i3e6115c5_expr_3 = global::System.Linq.Expressions.Expression.Constant(null, typeof(object)); // null
            var i3e6115c5_expr_2 = global::System.Linq.Expressions.Expression.Convert(i3e6115c5_expr_3, typeof(string));
            var i3e6115c5_expr_0 = global::System.Linq.Expressions.Expression.MakeBinary(global::System.Linq.Expressions.ExpressionType.NotEqual, i3e6115c5_expr_1, i3e6115c5_expr_2);
            var __lambda = global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer, bool>>(i3e6115c5_expr_0, i3e6115c5_p_c);
            return global::ExpressiveSharp.ExpressiveQueryableExtensions.AsExpressive(
                global::System.Linq.Queryable.Where(
                    (global::System.Linq.IQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer>)source,
                    __lambda));
        }
    }
}

namespace System.Runtime.CompilerServices
{
    [global::System.AttributeUsage(global::System.AttributeTargets.Method, AllowMultiple = true)]
    file sealed class InterceptsLocationAttribute : global::System.Attribute
    {
        public InterceptsLocationAttribute(int version, string data) { }
    }
}

Open in Playground →

db
    .Customers
    .Where(c => c.Country != null)
    .Select(c => new CustomerDto(c))

// Setup
public class CustomerDto
{
    public int Id { get; set; }
    public string Name { get; set; } = "";
    public string? Country { get; set; }
    public int OrderCount { get; set; }

    public CustomerDto() { }

    [Expressive]
    public CustomerDto(Customer c)
    {
        Id = c.Id;
        Name = c.Name;
        Country = c.Country;
        OrderCount = c.Orders.Count();
    }
}

Generated SQL:

SELECT "c"."Id", "c"."Name", "c"."Country", (
    SELECT COUNT(*)
    FROM "Orders" AS "o"
    WHERE "c"."Id" = "o"."CustomerId") AS "OrderCount"
FROM "Customers" AS "c"
WHERE "c"."Country" IS NOT NULL

The constructor body is inlined as SQL -- no data is fetched to memory for the projection.

Basic Constructor Projection: OrderSummaryDto

A straightforward example showing how constructor parameters map to SQL expressions:

C#

db
    .Orders
    .Select(o => new OrderSummaryDto(o.Id, o.Status.ToString(), o.ItemCount()))

// Setup
public static class OrderExt
{
    [Expressive]
    public static int ItemCount(this Order o) => o.Items.Count();
}

public class OrderSummaryDto
{
    public int Id { get; set; }
    public string Description { get; set; } = "";
    public int Items { get; set; }

    public OrderSummaryDto() { }

    [Expressive]
    public OrderSummaryDto(int id, string description, int items)
    {
        Id = id;
        Description = description;
        Items = items;
    }
}

SELECT "o"."Id", CASE
    WHEN "o"."Status" = 0 THEN 'Pending'
    WHEN "o"."Status" = 1 THEN 'Paid'
    WHEN "o"."Status" = 2 THEN 'Shipped'
    WHEN "o"."Status" = 3 THEN 'Delivered'
    WHEN "o"."Status" = 4 THEN 'Refunded'
END AS "Description", (
    SELECT COUNT(*)
    FROM "LineItems" AS "l"
    WHERE "o"."Id" = "l"."OrderId") AS "Items"
FROM "Orders" AS "o"

SELECT o."Id", CASE
    WHEN o."Status" = 0 THEN 'Pending'
    WHEN o."Status" = 1 THEN 'Paid'
    WHEN o."Status" = 2 THEN 'Shipped'
    WHEN o."Status" = 3 THEN 'Delivered'
    WHEN o."Status" = 4 THEN 'Refunded'
END AS "Description", (
    SELECT count(*)::int
    FROM "LineItems" AS l
    WHERE o."Id" = l."OrderId") AS "Items"
FROM "Orders" AS o

SELECT [o].[Id], CASE
    WHEN [o].[Status] = 0 THEN N'Pending'
    WHEN [o].[Status] = 1 THEN N'Paid'
    WHEN [o].[Status] = 2 THEN N'Shipped'
    WHEN [o].[Status] = 3 THEN N'Delivered'
    WHEN [o].[Status] = 4 THEN N'Refunded'
END AS [Description], (
    SELECT COUNT(*)
    FROM [LineItems] AS [l]
    WHERE [o].[Id] = [l].[OrderId]) AS [Items]
FROM [Orders] AS [o]

playground.orders.Aggregate([
    {
         "$project" : {
             "_id" : "$_id",
            "Description" : {
                 "$cond" : {
                     "if" : {
                         "$eq" : ["$Status", 0] 
                    },
                    "then" : "Pending",
                    "else" : {
                         "$cond" : {
                             "if" : {
                                 "$eq" : ["$Status", 1] 
                            },
                            "then" : "Paid",
                            "else" : {
                                 "$cond" : {
                                     "if" : {
                                         "$eq" : ["$Status", 2] 
                                    },
                                    "then" : "Shipped",
                                    "else" : {
                                         "$cond" : {
                                             "if" : {
                                                 "$eq" : ["$Status", 3] 
                                            },
                                            "then" : "Delivered",
                                            "else" : {
                                                 "$cond" : {
                                                     "if" : {
                                                         "$eq" : ["$Status", 4] 
                                                    },
                                                    "then" : "Refunded",
                                                    "else" : null 
                                                } 
                                            } 
                                        } 
                                    } 
                                } 
                            } 
                        } 
                    } 
                } 
            },
            "Items" : { "$size" : "$Items" } 
        } 
    }
])

// === ExpressiveSharp_Docs_Playground_Snippet_OrderExt.ItemCount_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Linq;
using System.Linq.Expressions;
using ExpressiveSharp;
using ExpressiveSharp.EntityFrameworkCore;
using ExpressiveSharp.Docs.PlaygroundModel.Webshop;
using ExpressiveSharp.Docs.Playground.Snippet;

namespace ExpressiveSharp.Generated
{
    static partial class ExpressiveSharp_Docs_Playground_Snippet_OrderExt 
    {
        // [Expressive]
        // public static int ItemCount(this Order o) => o.Items.Count();
        static global::System.Linq.Expressions.Expression<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, int>> ItemCount_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order_Expression() 
        {
            var p_o = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order), "o");
            var expr_1 = global::System.Linq.Expressions.Expression.Property(p_o, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order).GetProperty("Items", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // o.Items
            var expr_0 = global::System.Linq.Expressions.Expression.Call(global::System.Linq.Enumerable.First(global::System.Linq.Enumerable.Where(typeof(global::System.Linq.Enumerable).GetMethods(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static), m => m.Name == "Count" && m.IsGenericMethodDefinition && m.GetGenericArguments().Length == 1 && m.GetParameters().Length == 1 && m.GetParameters()[0].ParameterType.IsGenericType && !m.GetParameters()[0].ParameterType.IsGenericParameter)).MakeGenericMethod(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.LineItem)), new global::System.Linq.Expressions.Expression[] { expr_1 });
            return global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, int>>(expr_0, p_o);
        }
    }
}


// === ExpressiveSharp_Docs_Playground_Snippet_OrderSummaryDto._ctor_P0_int_P1_string_P2_int.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Linq;
using System.Linq.Expressions;
using ExpressiveSharp;
using ExpressiveSharp.EntityFrameworkCore;
using ExpressiveSharp.Docs.PlaygroundModel.Webshop;
using ExpressiveSharp.Docs.Playground.Snippet;

namespace ExpressiveSharp.Generated
{
    static partial class ExpressiveSharp_Docs_Playground_Snippet_OrderSummaryDto 
    {
        // [Expressive]
        // public OrderSummaryDto(int id, string description, int items)
        // {
        //     Id = id;
        //     Description = description;
        //     Items = items;
        // }
        static global::System.Linq.Expressions.Expression<global::System.Func<int, string, int, global::ExpressiveSharp.Docs.Playground.Snippet.OrderSummaryDto>> _ctor_P0_int_P1_string_P2_int_Expression() 
        {
            var p_id = global::System.Linq.Expressions.Expression.Parameter(typeof(int), "id");
            var p_description = global::System.Linq.Expressions.Expression.Parameter(typeof(string), "description");
            var p_items = global::System.Linq.Expressions.Expression.Parameter(typeof(int), "items");
            var expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderSummaryDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null));
            var expr_1 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderSummaryDto).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), p_id);
            var expr_2 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderSummaryDto).GetProperty("Description", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), p_description);
            var expr_3 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderSummaryDto).GetProperty("Items", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), p_items);
            var expr_4 = global::System.Linq.Expressions.Expression.MemberInit(expr_0, expr_1, expr_2, expr_3);
            return global::System.Linq.Expressions.Expression.Lambda<global::System.Func<int, string, int, global::ExpressiveSharp.Docs.Playground.Snippet.OrderSummaryDto>>(expr_4, p_id, p_description, p_items);
        }
    }
}


// === ExpressiveSharp_Docs_Playground_Snippet_OrderExt.Attributes.g.cs ===
// <auto-generated/>

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    static partial class ExpressiveSharp_Docs_Playground_Snippet_OrderExt { }
}


// === ExpressiveSharp_Docs_Playground_Snippet_OrderSummaryDto.Attributes.g.cs ===
// <auto-generated/>

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    static partial class ExpressiveSharp_Docs_Playground_Snippet_OrderSummaryDto { }
}


// === ExpressionRegistry.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Reflection;

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    internal static class ExpressionRegistry
    {
        private static Dictionary<nint, LambdaExpression> Build()
        {
            const BindingFlags allFlags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static;
            var map = new Dictionary<nint, LambdaExpression>();
            
            Register(map, typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderExt).GetMethod("ItemCount", allFlags, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order) }, null), "ExpressiveSharp.Generated.ExpressiveSharp_Docs_Playground_Snippet_OrderExt", "ItemCount_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order_Expression");
            Register(map, typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderSummaryDto).GetConstructor(allFlags, null, new global::System.Type[] { typeof(int), typeof(string), typeof(int) }, null), "ExpressiveSharp.Generated.ExpressiveSharp_Docs_Playground_Snippet_OrderSummaryDto", "_ctor_P0_int_P1_string_P2_int_Expression");
            
            return map;
        }
        
        private static volatile Dictionary<nint, LambdaExpression> _map = Build();
        
        internal static void ResetMap() => _map = Build();
        
        public static LambdaExpression TryGet(MemberInfo member)
        {
            var handle = member switch
            {
                MethodInfo m      => (nint?)m.MethodHandle.Value,
                PropertyInfo p    => p.GetMethod?.MethodHandle.Value,
                ConstructorInfo c => (nint?)c.MethodHandle.Value,
                _                 => null
            };
            
            return handle.HasValue && _map.TryGetValue(handle.Value, out var expr) ? expr : null;
        }
        
        private static void Register(Dictionary<nint, LambdaExpression> map, MethodBase m, string exprClass, string exprMethodName)
        {
            if (m is null) return;
            var exprType = m.DeclaringType?.Assembly.GetType(exprClass) ?? typeof(ExpressionRegistry).Assembly.GetType(exprClass);
            var exprMethod = exprType?.GetMethod(exprMethodName, BindingFlags.Static | BindingFlags.NonPublic);
            if (exprMethod is null) return;
            var expr = (LambdaExpression)exprMethod.Invoke(null, null)!;
            
            // Apply declared transformers from the generated class (if any)
            const string expressionSuffix = "_Expression";
            if (exprMethodName.EndsWith(expressionSuffix, StringComparison.Ordinal))
            {
                var transformersSuffix = exprMethodName.Substring(0, exprMethodName.Length - expressionSuffix.Length) + "_Transformers";
                var transformersMethod = exprType.GetMethod(transformersSuffix, BindingFlags.Static | BindingFlags.NonPublic);
                if (transformersMethod?.Invoke(null, null) is global::ExpressiveSharp.IExpressionTreeTransformer[] transformers)
                {
                    Expression transformed = expr;
                    foreach (var t in transformers) transformed = t.Transform(transformed);
                    if (transformed is LambdaExpression lambdaResult) expr = lambdaResult;
                }
            }
            
            map[m.MethodHandle.Value] = expr;
        }
    }
}


// === PolyfillInterceptors_b1293e61.g.cs ===
// <auto-generated/>
#nullable disable

namespace ExpressiveSharp.Generated.Interceptors
{
    internal static partial class PolyfillInterceptors
    {
        [global::System.Runtime.CompilerServices.InterceptsLocationAttribute(1, "E25IToyGqhczBT73gX3lSYQBAABfX1NuaXBwZXQuY3M=")]
        internal static global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.Playground.Snippet.OrderSummaryDto> __Polyfill_Select_3e61_15_5(
            this global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order> source,
            global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, global::ExpressiveSharp.Docs.Playground.Snippet.OrderSummaryDto> __func)
        {
            // Source: o => new OrderSummaryDto(o.Id, o.Status.ToString(), o.ItemCount())
            var i3e6115c5_p_o = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order), "o");
            var i3e6115c5_expr_1 = global::System.Linq.Expressions.Expression.Property(i3e6115c5_p_o, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // o.Id
            var i3e6115c5_expr_2 = global::System.Linq.Expressions.Expression.Property(i3e6115c5_p_o, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order).GetProperty("Status", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // o.Status
            var i3e6115c5_expr_3 = global::System.Linq.Expressions.Expression.Constant(null, typeof(string));
            var i3e6115c5_expr_4 = global::System.Linq.Expressions.Expression.Constant(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.OrderStatus.Refunded, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.OrderStatus));
            var i3e6115c5_expr_5 = global::System.Linq.Expressions.Expression.Call(i3e6115c5_expr_4, typeof(global::System.Enum).GetMethod("ToString", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null), global::System.Array.Empty<global::System.Linq.Expressions.Expression>());
            var i3e6115c5_expr_6 = global::System.Linq.Expressions.Expression.Equal(i3e6115c5_expr_2, i3e6115c5_expr_4);
            var i3e6115c5_expr_7 = global::System.Linq.Expressions.Expression.Condition(i3e6115c5_expr_6, i3e6115c5_expr_5, i3e6115c5_expr_3, typeof(string));
            var i3e6115c5_expr_8 = global::System.Linq.Expressions.Expression.Constant(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.OrderStatus.Delivered, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.OrderStatus));
            var i3e6115c5_expr_9 = global::System.Linq.Expressions.Expression.Call(i3e6115c5_expr_8, typeof(global::System.Enum).GetMethod("ToString", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null), global::System.Array.Empty<global::System.Linq.Expressions.Expression>());
            var i3e6115c5_expr_10 = global::System.Linq.Expressions.Expression.Equal(i3e6115c5_expr_2, i3e6115c5_expr_8);
            var i3e6115c5_expr_11 = global::System.Linq.Expressions.Expression.Condition(i3e6115c5_expr_10, i3e6115c5_expr_9, i3e6115c5_expr_7, typeof(string));
            var i3e6115c5_expr_12 = global::System.Linq.Expressions.Expression.Constant(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.OrderStatus.Shipped, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.OrderStatus));
            var i3e6115c5_expr_13 = global::System.Linq.Expressions.Expression.Call(i3e6115c5_expr_12, typeof(global::System.Enum).GetMethod("ToString", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null), global::System.Array.Empty<global::System.Linq.Expressions.Expression>());
            var i3e6115c5_expr_14 = global::System.Linq.Expressions.Expression.Equal(i3e6115c5_expr_2, i3e6115c5_expr_12);
            var i3e6115c5_expr_15 = global::System.Linq.Expressions.Expression.Condition(i3e6115c5_expr_14, i3e6115c5_expr_13, i3e6115c5_expr_11, typeof(string));
            var i3e6115c5_expr_16 = global::System.Linq.Expressions.Expression.Constant(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.OrderStatus.Paid, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.OrderStatus));
            var i3e6115c5_expr_17 = global::System.Linq.Expressions.Expression.Call(i3e6115c5_expr_16, typeof(global::System.Enum).GetMethod("ToString", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null), global::System.Array.Empty<global::System.Linq.Expressions.Expression>());
            var i3e6115c5_expr_18 = global::System.Linq.Expressions.Expression.Equal(i3e6115c5_expr_2, i3e6115c5_expr_16);
            var i3e6115c5_expr_19 = global::System.Linq.Expressions.Expression.Condition(i3e6115c5_expr_18, i3e6115c5_expr_17, i3e6115c5_expr_15, typeof(string));
            var i3e6115c5_expr_20 = global::System.Linq.Expressions.Expression.Constant(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.OrderStatus.Pending, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.OrderStatus));
            var i3e6115c5_expr_21 = global::System.Linq.Expressions.Expression.Call(i3e6115c5_expr_20, typeof(global::System.Enum).GetMethod("ToString", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null), global::System.Array.Empty<global::System.Linq.Expressions.Expression>());
            var i3e6115c5_expr_22 = global::System.Linq.Expressions.Expression.Equal(i3e6115c5_expr_2, i3e6115c5_expr_20);
            var i3e6115c5_expr_23 = global::System.Linq.Expressions.Expression.Condition(i3e6115c5_expr_22, i3e6115c5_expr_21, i3e6115c5_expr_19, typeof(string));
            var i3e6115c5_expr_24 = global::System.Linq.Expressions.Expression.Call(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderExt).GetMethod("ItemCount", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order) }, null), new global::System.Linq.Expressions.Expression[] { i3e6115c5_p_o }); // o.ItemCount()
            var i3e6115c5_expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderSummaryDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] { typeof(int), typeof(string), typeof(int) }, null), i3e6115c5_expr_1, i3e6115c5_expr_23, i3e6115c5_expr_24);
            var __lambda = global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, global::ExpressiveSharp.Docs.Playground.Snippet.OrderSummaryDto>>(i3e6115c5_expr_0, i3e6115c5_p_o);
            return global::ExpressiveSharp.ExpressiveQueryableExtensions.AsExpressive(
                global::System.Linq.Queryable.Select(
                    (global::System.Linq.IQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order>)source,
                    __lambda));
        }
    }
}

namespace System.Runtime.CompilerServices
{
    [global::System.AttributeUsage(global::System.AttributeTargets.Method, AllowMultiple = true)]
    file sealed class InterceptsLocationAttribute : global::System.Attribute
    {
        public InterceptsLocationAttribute(int version, string data) { }
    }
}

Open in Playground →

db
    .Orders
    .Select(o => new OrderSummaryDto(o.Id, o.Status.ToString(), o.ItemCount()))

// Setup
public static class OrderExt
{
    [Expressive]
    public static int ItemCount(this Order o) => o.Items.Count();
}

public class OrderSummaryDto
{
    public int Id { get; set; }
    public string Description { get; set; } = "";
    public int Items { get; set; }

    public OrderSummaryDto() { }

    [Expressive]
    public OrderSummaryDto(int id, string description, int items)
    {
        Id = id;
        Description = description;
        Items = items;
    }
}

Generated SQL:

SELECT "o"."Id", CASE
    WHEN "o"."Status" = 0 THEN 'Pending'
    WHEN "o"."Status" = 1 THEN 'Paid'
    WHEN "o"."Status" = 2 THEN 'Shipped'
    WHEN "o"."Status" = 3 THEN 'Delivered'
    WHEN "o"."Status" = 4 THEN 'Refunded'
END AS "Description", (
    SELECT COUNT(*)
    FROM "LineItems" AS "l"
    WHERE "o"."Id" = "l"."OrderId") AS "Items"
FROM "Orders" AS "o"

TIP

Notice that o.ItemCount() is an [Expressive] extension method -- it gets expanded to o.Items.Count() automatically. Constructor projections compose naturally with computed members.

Inheritance Chains with Base Initializers

When your DTOs form an inheritance hierarchy, use : base(...) to avoid duplicating base-class assignments. The generator inlines both the base and derived assignments:

C#

db
    .Customers
    .Select(c => new PremiumCustomerDto(c))

// Setup
public class CustomerBaseDto
{
    public int Id { get; set; }
    public string Name { get; set; } = "";

    public CustomerBaseDto() { }

    [Expressive]
    public CustomerBaseDto(Customer c)
    {
        Id = c.Id;
        Name = c.Name;
    }
}

public class PremiumCustomerDto : CustomerBaseDto
{
    public string Country { get; set; } = "";
    public string Tier { get; set; } = "";

    public PremiumCustomerDto() { }

    [Expressive]
    public PremiumCustomerDto(Customer c) : base(c)
    {
        Country = c.Country ?? "Unknown";
        Tier = c.Orders.Count() >= 10 ? "Gold" : "Standard";
    }
}

SELECT COALESCE("c"."Country", 'Unknown') AS "Country", CASE
    WHEN (
        SELECT COUNT(*)
        FROM "Orders" AS "o"
        WHERE "c"."Id" = "o"."CustomerId") >= 10 THEN 'Gold'
    ELSE 'Standard'
END AS "Tier"
FROM "Customers" AS "c"

SELECT COALESCE(c."Country", 'Unknown') AS "Country", CASE
    WHEN (
        SELECT count(*)::int
        FROM "Orders" AS o
        WHERE c."Id" = o."CustomerId") >= 10 THEN 'Gold'
    ELSE 'Standard'
END AS "Tier"
FROM "Customers" AS c

SELECT COALESCE([c].[Country], N'Unknown') AS [Country], CASE
    WHEN (
        SELECT COUNT(*)
        FROM [Orders] AS [o]
        WHERE [c].[Id] = [o].[CustomerId]) >= 10 THEN N'Gold'
    ELSE N'Standard'
END AS [Tier]
FROM [Customers] AS [c]

playground.customers.Aggregate([
    {
         "$project" : {
             "Country" : {
                 "$ifNull" : ["$Country", "Unknown"] 
            },
            "Tier" : {
                 "$cond" : {
                     "if" : {
                         "$gte" : [
                            { "$size" : "$Orders" },
                            10
                        ] 
                    },
                    "then" : "Gold",
                    "else" : "Standard" 
                } 
            },
            "_id" : 0 
        } 
    }
])

// === ExpressiveSharp_Docs_Playground_Snippet_CustomerBaseDto._ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Customer.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Linq;
using System.Linq.Expressions;
using ExpressiveSharp;
using ExpressiveSharp.EntityFrameworkCore;
using ExpressiveSharp.Docs.PlaygroundModel.Webshop;
using ExpressiveSharp.Docs.Playground.Snippet;

namespace ExpressiveSharp.Generated
{
    static partial class ExpressiveSharp_Docs_Playground_Snippet_CustomerBaseDto 
    {
        // [Expressive]
        // public CustomerBaseDto(Customer c)
        // {
        //     Id = c.Id;
        //     Name = c.Name;
        // }
        static global::System.Linq.Expressions.Expression<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer, global::ExpressiveSharp.Docs.Playground.Snippet.CustomerBaseDto>> _ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Customer_Expression() 
        {
            var p_c = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer), "c");
            var expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.CustomerBaseDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null));
            var expr_1 = global::System.Linq.Expressions.Expression.Property(p_c, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // c.Id
            var expr_2 = global::System.Linq.Expressions.Expression.Property(p_c, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer).GetProperty("Name", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // c.Name
            var expr_3 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.CustomerBaseDto).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_1);
            var expr_4 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.CustomerBaseDto).GetProperty("Name", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_2);
            var expr_5 = global::System.Linq.Expressions.Expression.MemberInit(expr_0, expr_3, expr_4);
            return global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer, global::ExpressiveSharp.Docs.Playground.Snippet.CustomerBaseDto>>(expr_5, p_c);
        }
    }
}


// === ExpressiveSharp_Docs_Playground_Snippet_PremiumCustomerDto._ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Customer.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Linq;
using System.Linq.Expressions;
using ExpressiveSharp;
using ExpressiveSharp.EntityFrameworkCore;
using ExpressiveSharp.Docs.PlaygroundModel.Webshop;
using ExpressiveSharp.Docs.Playground.Snippet;

namespace ExpressiveSharp.Generated
{
    static partial class ExpressiveSharp_Docs_Playground_Snippet_PremiumCustomerDto 
    {
        // [Expressive]
        // public PremiumCustomerDto(Customer c) : base(c)
        // {
        //     Country = c.Country ?? "Unknown";
        //     Tier = c.Orders.Count() >= 10 ? "Gold" : "Standard";
        // }
        static global::System.Linq.Expressions.Expression<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer, global::ExpressiveSharp.Docs.Playground.Snippet.PremiumCustomerDto>> _ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Customer_Expression() 
        {
            var p_c = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer), "c");
            var expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.PremiumCustomerDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null));
            var expr_2 = global::System.Linq.Expressions.Expression.Property(p_c, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer).GetProperty("Country", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // c.Country
            var expr_3 = global::System.Linq.Expressions.Expression.Constant("Unknown", typeof(string)); // "Unknown"
            var expr_1 = global::System.Linq.Expressions.Expression.Coalesce(expr_2, expr_3);
            var expr_7 = global::System.Linq.Expressions.Expression.Property(p_c, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer).GetProperty("Orders", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // c.Orders
            var expr_6 = global::System.Linq.Expressions.Expression.Call(global::System.Linq.Enumerable.First(global::System.Linq.Enumerable.Where(typeof(global::System.Linq.Enumerable).GetMethods(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static), m => m.Name == "Count" && m.IsGenericMethodDefinition && m.GetGenericArguments().Length == 1 && m.GetParameters().Length == 1 && m.GetParameters()[0].ParameterType.IsGenericType && !m.GetParameters()[0].ParameterType.IsGenericParameter)).MakeGenericMethod(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order)), new global::System.Linq.Expressions.Expression[] { expr_7 });
            var expr_8 = global::System.Linq.Expressions.Expression.Constant(10, typeof(int)); // 10
            var expr_5 = global::System.Linq.Expressions.Expression.MakeBinary(global::System.Linq.Expressions.ExpressionType.GreaterThanOrEqual, expr_6, expr_8);
            var expr_9 = global::System.Linq.Expressions.Expression.Constant("Gold", typeof(string)); // "Gold"
            var expr_10 = global::System.Linq.Expressions.Expression.Constant("Standard", typeof(string)); // "Standard"
            var expr_4 = global::System.Linq.Expressions.Expression.Condition(expr_5, expr_9, expr_10, typeof(string));
            var expr_11 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.PremiumCustomerDto).GetProperty("Country", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_1);
            var expr_12 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.PremiumCustomerDto).GetProperty("Tier", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_4);
            var expr_13 = global::System.Linq.Expressions.Expression.MemberInit(expr_0, expr_11, expr_12);
            return global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer, global::ExpressiveSharp.Docs.Playground.Snippet.PremiumCustomerDto>>(expr_13, p_c);
        }
    }
}


// === ExpressiveSharp_Docs_Playground_Snippet_CustomerBaseDto.Attributes.g.cs ===
// <auto-generated/>

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    static partial class ExpressiveSharp_Docs_Playground_Snippet_CustomerBaseDto { }
}


// === ExpressiveSharp_Docs_Playground_Snippet_PremiumCustomerDto.Attributes.g.cs ===
// <auto-generated/>

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    static partial class ExpressiveSharp_Docs_Playground_Snippet_PremiumCustomerDto { }
}


// === ExpressionRegistry.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Reflection;

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    internal static class ExpressionRegistry
    {
        private static Dictionary<nint, LambdaExpression> Build()
        {
            const BindingFlags allFlags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static;
            var map = new Dictionary<nint, LambdaExpression>();
            
            Register(map, typeof(global::ExpressiveSharp.Docs.Playground.Snippet.CustomerBaseDto).GetConstructor(allFlags, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer) }, null), "ExpressiveSharp.Generated.ExpressiveSharp_Docs_Playground_Snippet_CustomerBaseDto", "_ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Customer_Expression");
            Register(map, typeof(global::ExpressiveSharp.Docs.Playground.Snippet.PremiumCustomerDto).GetConstructor(allFlags, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer) }, null), "ExpressiveSharp.Generated.ExpressiveSharp_Docs_Playground_Snippet_PremiumCustomerDto", "_ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Customer_Expression");
            
            return map;
        }
        
        private static volatile Dictionary<nint, LambdaExpression> _map = Build();
        
        internal static void ResetMap() => _map = Build();
        
        public static LambdaExpression TryGet(MemberInfo member)
        {
            var handle = member switch
            {
                MethodInfo m      => (nint?)m.MethodHandle.Value,
                PropertyInfo p    => p.GetMethod?.MethodHandle.Value,
                ConstructorInfo c => (nint?)c.MethodHandle.Value,
                _                 => null
            };
            
            return handle.HasValue && _map.TryGetValue(handle.Value, out var expr) ? expr : null;
        }
        
        private static void Register(Dictionary<nint, LambdaExpression> map, MethodBase m, string exprClass, string exprMethodName)
        {
            if (m is null) return;
            var exprType = m.DeclaringType?.Assembly.GetType(exprClass) ?? typeof(ExpressionRegistry).Assembly.GetType(exprClass);
            var exprMethod = exprType?.GetMethod(exprMethodName, BindingFlags.Static | BindingFlags.NonPublic);
            if (exprMethod is null) return;
            var expr = (LambdaExpression)exprMethod.Invoke(null, null)!;
            
            // Apply declared transformers from the generated class (if any)
            const string expressionSuffix = "_Expression";
            if (exprMethodName.EndsWith(expressionSuffix, StringComparison.Ordinal))
            {
                var transformersSuffix = exprMethodName.Substring(0, exprMethodName.Length - expressionSuffix.Length) + "_Transformers";
                var transformersMethod = exprType.GetMethod(transformersSuffix, BindingFlags.Static | BindingFlags.NonPublic);
                if (transformersMethod?.Invoke(null, null) is global::ExpressiveSharp.IExpressionTreeTransformer[] transformers)
                {
                    Expression transformed = expr;
                    foreach (var t in transformers) transformed = t.Transform(transformed);
                    if (transformed is LambdaExpression lambdaResult) expr = lambdaResult;
                }
            }
            
            map[m.MethodHandle.Value] = expr;
        }
    }
}


// === PolyfillInterceptors_b1293e61.g.cs ===
// <auto-generated/>
#nullable disable

namespace ExpressiveSharp.Generated.Interceptors
{
    internal static partial class PolyfillInterceptors
    {
        [global::System.Runtime.CompilerServices.InterceptsLocationAttribute(1, "Y1w7nzu5Zw8OZDRhhkL61IIBAABfX1NuaXBwZXQuY3M=")]
        internal static global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.Playground.Snippet.PremiumCustomerDto> __Polyfill_Select_3e61_14_24(
            this global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer> source,
            global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer, global::ExpressiveSharp.Docs.Playground.Snippet.PremiumCustomerDto> __func)
        {
            // Source: c => new PremiumCustomerDto(c)
            var i3e6114c24_p_c = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer), "c");
            var i3e6114c24_expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.PremiumCustomerDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer) }, null), i3e6114c24_p_c); // new PremiumCustomerDto(c)
            var __lambda = global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer, global::ExpressiveSharp.Docs.Playground.Snippet.PremiumCustomerDto>>(i3e6114c24_expr_0, i3e6114c24_p_c);
            return global::ExpressiveSharp.ExpressiveQueryableExtensions.AsExpressive(
                global::System.Linq.Queryable.Select(
                    (global::System.Linq.IQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer>)source,
                    __lambda));
        }
    }
}

namespace System.Runtime.CompilerServices
{
    [global::System.AttributeUsage(global::System.AttributeTargets.Method, AllowMultiple = true)]
    file sealed class InterceptsLocationAttribute : global::System.Attribute
    {
        public InterceptsLocationAttribute(int version, string data) { }
    }
}

Open in Playground →

db
    .Customers
    .Select(c => new PremiumCustomerDto(c))

// Setup
public class CustomerBaseDto
{
    public int Id { get; set; }
    public string Name { get; set; } = "";

    public CustomerBaseDto() { }

    [Expressive]
    public CustomerBaseDto(Customer c)
    {
        Id = c.Id;
        Name = c.Name;
    }
}

public class PremiumCustomerDto : CustomerBaseDto
{
    public string Country { get; set; } = "";
    public string Tier { get; set; } = "";

    public PremiumCustomerDto() { }

    [Expressive]
    public PremiumCustomerDto(Customer c) : base(c)
    {
        Country = c.Country ?? "Unknown";
        Tier = c.Orders.Count() >= 10 ? "Gold" : "Standard";
    }
}

Generated SQL:

SELECT COALESCE("c"."Country", 'Unknown') AS "Country", CASE
    WHEN (
        SELECT COUNT(*)
        FROM "Orders" AS "o"
        WHERE "c"."Id" = "o"."CustomerId") >= 10 THEN 'Gold'
    ELSE 'Standard'
END AS "Tier"
FROM "Customers" AS "c"

All fields -- Id, Name, Country, and Tier -- are projected in a single query.

Constructor Overloads

If you need different projections from the same DTO, use constructor overloads. Each gets its own generated expression:

C#

db
    .Orders
    .Select(o => new OrderDto(o))

// Setup
public class OrderDto
{
    public int Id { get; set; }
    public int ItemCount { get; set; }
    public string? CustomerName { get; set; }

    public OrderDto() { }

    // Full projection (with customer name -- requires navigation join)
    [Expressive]
    public OrderDto(Order o)
    {
        Id = o.Id;
        ItemCount = o.Items.Count();
        CustomerName = o.Customer.Name;
    }

    // Lightweight projection (no navigation join needed)
    [Expressive]
    public OrderDto(Order o, bool lightweight)
    {
        Id = o.Id;
        ItemCount = o.Items.Count();
        CustomerName = null;
    }
}

SELECT "o"."Id", (
    SELECT COUNT(*)
    FROM "LineItems" AS "l"
    WHERE "o"."Id" = "l"."OrderId") AS "ItemCount", "c"."Name" AS "CustomerName"
FROM "Orders" AS "o"
INNER JOIN "Customers" AS "c" ON "o"."CustomerId" = "c"."Id"

SELECT o."Id", (
    SELECT count(*)::int
    FROM "LineItems" AS l
    WHERE o."Id" = l."OrderId") AS "ItemCount", c."Name" AS "CustomerName"
FROM "Orders" AS o
INNER JOIN "Customers" AS c ON o."CustomerId" = c."Id"

SELECT [o].[Id], (
    SELECT COUNT(*)
    FROM [LineItems] AS [l]
    WHERE [o].[Id] = [l].[OrderId]) AS [ItemCount], [c].[Name] AS [CustomerName]
FROM [Orders] AS [o]
INNER JOIN [Customers] AS [c] ON [o].[CustomerId] = [c].[Id]

playground.orders.Aggregate([
    {
         "$project" : {
             "_id" : "$_id",
            "ItemCount" : { "$size" : "$Items" },
            "CustomerName" : "$Customer.Name" 
        } 
    }
])

// === ExpressiveSharp_Docs_Playground_Snippet_OrderDto._ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Linq;
using System.Linq.Expressions;
using ExpressiveSharp;
using ExpressiveSharp.EntityFrameworkCore;
using ExpressiveSharp.Docs.PlaygroundModel.Webshop;
using ExpressiveSharp.Docs.Playground.Snippet;

namespace ExpressiveSharp.Generated
{
    static partial class ExpressiveSharp_Docs_Playground_Snippet_OrderDto 
    {
        // // Full projection (with customer name -- requires navigation join)
        // [Expressive]
        // public OrderDto(Order o)
        // {
        //     Id = o.Id;
        //     ItemCount = o.Items.Count();
        //     CustomerName = o.Customer.Name;
        // }
        static global::System.Linq.Expressions.Expression<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto>> _ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order_Expression() 
        {
            var p_o = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order), "o");
            var expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null));
            var expr_1 = global::System.Linq.Expressions.Expression.Property(p_o, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // o.Id
            var expr_3 = global::System.Linq.Expressions.Expression.Property(p_o, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order).GetProperty("Items", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // o.Items
            var expr_2 = global::System.Linq.Expressions.Expression.Call(global::System.Linq.Enumerable.First(global::System.Linq.Enumerable.Where(typeof(global::System.Linq.Enumerable).GetMethods(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static), m => m.Name == "Count" && m.IsGenericMethodDefinition && m.GetGenericArguments().Length == 1 && m.GetParameters().Length == 1 && m.GetParameters()[0].ParameterType.IsGenericType && !m.GetParameters()[0].ParameterType.IsGenericParameter)).MakeGenericMethod(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.LineItem)), new global::System.Linq.Expressions.Expression[] { expr_3 });
            var expr_5 = global::System.Linq.Expressions.Expression.Property(p_o, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order).GetProperty("Customer", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // o.Customer
            var expr_4 = global::System.Linq.Expressions.Expression.Property(expr_5, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer).GetProperty("Name", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance));
            var expr_6 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_1);
            var expr_7 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetProperty("ItemCount", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_2);
            var expr_8 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetProperty("CustomerName", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_4);
            var expr_9 = global::System.Linq.Expressions.Expression.MemberInit(expr_0, expr_6, expr_7, expr_8);
            return global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto>>(expr_9, p_o);
        }
    }
}


// === ExpressiveSharp_Docs_Playground_Snippet_OrderDto._ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order_P1_bool.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Linq;
using System.Linq.Expressions;
using ExpressiveSharp;
using ExpressiveSharp.EntityFrameworkCore;
using ExpressiveSharp.Docs.PlaygroundModel.Webshop;
using ExpressiveSharp.Docs.Playground.Snippet;

namespace ExpressiveSharp.Generated
{
    static partial class ExpressiveSharp_Docs_Playground_Snippet_OrderDto 
    {
        // // Lightweight projection (no navigation join needed)
        // [Expressive]
        // public OrderDto(Order o, bool lightweight)
        // {
        //     Id = o.Id;
        //     ItemCount = o.Items.Count();
        //     CustomerName = null;
        // }
        static global::System.Linq.Expressions.Expression<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, bool, global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto>> _ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order_P1_bool_Expression() 
        {
            var p_o = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order), "o");
            var p_lightweight = global::System.Linq.Expressions.Expression.Parameter(typeof(bool), "lightweight");
            var expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null));
            var expr_1 = global::System.Linq.Expressions.Expression.Property(p_o, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // o.Id
            var expr_3 = global::System.Linq.Expressions.Expression.Property(p_o, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order).GetProperty("Items", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // o.Items
            var expr_2 = global::System.Linq.Expressions.Expression.Call(global::System.Linq.Enumerable.First(global::System.Linq.Enumerable.Where(typeof(global::System.Linq.Enumerable).GetMethods(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static), m => m.Name == "Count" && m.IsGenericMethodDefinition && m.GetGenericArguments().Length == 1 && m.GetParameters().Length == 1 && m.GetParameters()[0].ParameterType.IsGenericType && !m.GetParameters()[0].ParameterType.IsGenericParameter)).MakeGenericMethod(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.LineItem)), new global::System.Linq.Expressions.Expression[] { expr_3 });
            var expr_5 = global::System.Linq.Expressions.Expression.Constant(null, typeof(object)); // null
            var expr_4 = global::System.Linq.Expressions.Expression.Convert(expr_5, typeof(string));
            var expr_6 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_1);
            var expr_7 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetProperty("ItemCount", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_2);
            var expr_8 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetProperty("CustomerName", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_4);
            var expr_9 = global::System.Linq.Expressions.Expression.MemberInit(expr_0, expr_6, expr_7, expr_8);
            return global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, bool, global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto>>(expr_9, p_o, p_lightweight);
        }
    }
}


// === ExpressiveSharp_Docs_Playground_Snippet_OrderDto.Attributes.g.cs ===
// <auto-generated/>

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    static partial class ExpressiveSharp_Docs_Playground_Snippet_OrderDto { }
}


// === ExpressionRegistry.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Reflection;

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    internal static class ExpressionRegistry
    {
        private static Dictionary<nint, LambdaExpression> Build()
        {
            const BindingFlags allFlags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static;
            var map = new Dictionary<nint, LambdaExpression>();
            
            Register(map, typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetConstructor(allFlags, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order) }, null), "ExpressiveSharp.Generated.ExpressiveSharp_Docs_Playground_Snippet_OrderDto", "_ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order_Expression");
            Register(map, typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetConstructor(allFlags, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order), typeof(bool) }, null), "ExpressiveSharp.Generated.ExpressiveSharp_Docs_Playground_Snippet_OrderDto", "_ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order_P1_bool_Expression");
            
            return map;
        }
        
        private static volatile Dictionary<nint, LambdaExpression> _map = Build();
        
        internal static void ResetMap() => _map = Build();
        
        public static LambdaExpression TryGet(MemberInfo member)
        {
            var handle = member switch
            {
                MethodInfo m      => (nint?)m.MethodHandle.Value,
                PropertyInfo p    => p.GetMethod?.MethodHandle.Value,
                ConstructorInfo c => (nint?)c.MethodHandle.Value,
                _                 => null
            };
            
            return handle.HasValue && _map.TryGetValue(handle.Value, out var expr) ? expr : null;
        }
        
        private static void Register(Dictionary<nint, LambdaExpression> map, MethodBase m, string exprClass, string exprMethodName)
        {
            if (m is null) return;
            var exprType = m.DeclaringType?.Assembly.GetType(exprClass) ?? typeof(ExpressionRegistry).Assembly.GetType(exprClass);
            var exprMethod = exprType?.GetMethod(exprMethodName, BindingFlags.Static | BindingFlags.NonPublic);
            if (exprMethod is null) return;
            var expr = (LambdaExpression)exprMethod.Invoke(null, null)!;
            
            // Apply declared transformers from the generated class (if any)
            const string expressionSuffix = "_Expression";
            if (exprMethodName.EndsWith(expressionSuffix, StringComparison.Ordinal))
            {
                var transformersSuffix = exprMethodName.Substring(0, exprMethodName.Length - expressionSuffix.Length) + "_Transformers";
                var transformersMethod = exprType.GetMethod(transformersSuffix, BindingFlags.Static | BindingFlags.NonPublic);
                if (transformersMethod?.Invoke(null, null) is global::ExpressiveSharp.IExpressionTreeTransformer[] transformers)
                {
                    Expression transformed = expr;
                    foreach (var t in transformers) transformed = t.Transform(transformed);
                    if (transformed is LambdaExpression lambdaResult) expr = lambdaResult;
                }
            }
            
            map[m.MethodHandle.Value] = expr;
        }
    }
}


// === PolyfillInterceptors_b1293e61.g.cs ===
// <auto-generated/>
#nullable disable

namespace ExpressiveSharp.Generated.Interceptors
{
    internal static partial class PolyfillInterceptors
    {
        [global::System.Runtime.CompilerServices.InterceptsLocationAttribute(1, "vI6GeV3uhuEkEnCq8l4Ban8BAABfX1NuaXBwZXQuY3M=")]
        internal static global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto> __Polyfill_Select_3e61_14_21(
            this global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order> source,
            global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto> __func)
        {
            // Source: o => new OrderDto(o)
            var i3e6114c21_p_o = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order), "o");
            var i3e6114c21_expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order) }, null), i3e6114c21_p_o); // new OrderDto(o)
            var __lambda = global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto>>(i3e6114c21_expr_0, i3e6114c21_p_o);
            return global::ExpressiveSharp.ExpressiveQueryableExtensions.AsExpressive(
                global::System.Linq.Queryable.Select(
                    (global::System.Linq.IQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order>)source,
                    __lambda));
        }
    }
}

namespace System.Runtime.CompilerServices
{
    [global::System.AttributeUsage(global::System.AttributeTargets.Method, AllowMultiple = true)]
    file sealed class InterceptsLocationAttribute : global::System.Attribute
    {
        public InterceptsLocationAttribute(int version, string data) { }
    }
}

Open in Playground →

db
    .Orders
    .Select(o => new OrderDto(o))

// Setup
public class OrderDto
{
    public int Id { get; set; }
    public int ItemCount { get; set; }
    public string? CustomerName { get; set; }

    public OrderDto() { }

    // Full projection (with customer name -- requires navigation join)
    [Expressive]
    public OrderDto(Order o)
    {
        Id = o.Id;
        ItemCount = o.Items.Count();
        CustomerName = o.Customer.Name;
    }

    // Lightweight projection (no navigation join needed)
    [Expressive]
    public OrderDto(Order o, bool lightweight)
    {
        Id = o.Id;
        ItemCount = o.Items.Count();
        CustomerName = null;
    }
}

Generated SQL:

SELECT "o"."Id", (
    SELECT COUNT(*)
    FROM "LineItems" AS "l"
    WHERE "o"."Id" = "l"."OrderId") AS "ItemCount", "c"."Name" AS "CustomerName"
FROM "Orders" AS "o"
INNER JOIN "Customers" AS "c" ON "o"."CustomerId" = "c"."Id"

The lightweight variant is called the same way, just with the extra argument:

C#

db
    .Orders
    .Select(o => new OrderDto(o, true))

// Setup
public class OrderDto
{
    public int Id { get; set; }
    public int ItemCount { get; set; }
    public string? CustomerName { get; set; }

    public OrderDto() { }

    [Expressive]
    public OrderDto(Order o)
    {
        Id = o.Id;
        ItemCount = o.Items.Count();
        CustomerName = o.Customer.Name;
    }

    [Expressive]
    public OrderDto(Order o, bool lightweight)
    {
        Id = o.Id;
        ItemCount = o.Items.Count();
        CustomerName = null;
    }
}

SELECT "o"."Id", (
    SELECT COUNT(*)
    FROM "LineItems" AS "l"
    WHERE "o"."Id" = "l"."OrderId") AS "ItemCount", NULL AS "CustomerName"
FROM "Orders" AS "o"

SELECT o."Id", (
    SELECT count(*)::int
    FROM "LineItems" AS l
    WHERE o."Id" = l."OrderId") AS "ItemCount", NULL AS "CustomerName"
FROM "Orders" AS o

SELECT [o].[Id], (
    SELECT COUNT(*)
    FROM [LineItems] AS [l]
    WHERE [o].[Id] = [l].[OrderId]) AS [ItemCount], NULL AS [CustomerName]
FROM [Orders] AS [o]

playground.orders.Aggregate([
    {
         "$project" : {
             "_id" : "$_id",
            "ItemCount" : { "$size" : "$Items" },
            "CustomerName" : null 
        } 
    }
])

// === ExpressiveSharp_Docs_Playground_Snippet_OrderDto._ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Linq;
using System.Linq.Expressions;
using ExpressiveSharp;
using ExpressiveSharp.EntityFrameworkCore;
using ExpressiveSharp.Docs.PlaygroundModel.Webshop;
using ExpressiveSharp.Docs.Playground.Snippet;

namespace ExpressiveSharp.Generated
{
    static partial class ExpressiveSharp_Docs_Playground_Snippet_OrderDto 
    {
        // [Expressive]
        // public OrderDto(Order o)
        // {
        //     Id = o.Id;
        //     ItemCount = o.Items.Count();
        //     CustomerName = o.Customer.Name;
        // }
        static global::System.Linq.Expressions.Expression<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto>> _ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order_Expression() 
        {
            var p_o = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order), "o");
            var expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null));
            var expr_1 = global::System.Linq.Expressions.Expression.Property(p_o, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // o.Id
            var expr_3 = global::System.Linq.Expressions.Expression.Property(p_o, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order).GetProperty("Items", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // o.Items
            var expr_2 = global::System.Linq.Expressions.Expression.Call(global::System.Linq.Enumerable.First(global::System.Linq.Enumerable.Where(typeof(global::System.Linq.Enumerable).GetMethods(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static), m => m.Name == "Count" && m.IsGenericMethodDefinition && m.GetGenericArguments().Length == 1 && m.GetParameters().Length == 1 && m.GetParameters()[0].ParameterType.IsGenericType && !m.GetParameters()[0].ParameterType.IsGenericParameter)).MakeGenericMethod(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.LineItem)), new global::System.Linq.Expressions.Expression[] { expr_3 });
            var expr_5 = global::System.Linq.Expressions.Expression.Property(p_o, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order).GetProperty("Customer", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // o.Customer
            var expr_4 = global::System.Linq.Expressions.Expression.Property(expr_5, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Customer).GetProperty("Name", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance));
            var expr_6 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_1);
            var expr_7 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetProperty("ItemCount", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_2);
            var expr_8 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetProperty("CustomerName", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_4);
            var expr_9 = global::System.Linq.Expressions.Expression.MemberInit(expr_0, expr_6, expr_7, expr_8);
            return global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto>>(expr_9, p_o);
        }
    }
}


// === ExpressiveSharp_Docs_Playground_Snippet_OrderDto._ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order_P1_bool.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Linq;
using System.Linq.Expressions;
using ExpressiveSharp;
using ExpressiveSharp.EntityFrameworkCore;
using ExpressiveSharp.Docs.PlaygroundModel.Webshop;
using ExpressiveSharp.Docs.Playground.Snippet;

namespace ExpressiveSharp.Generated
{
    static partial class ExpressiveSharp_Docs_Playground_Snippet_OrderDto 
    {
        // [Expressive]
        // public OrderDto(Order o, bool lightweight)
        // {
        //     Id = o.Id;
        //     ItemCount = o.Items.Count();
        //     CustomerName = null;
        // }
        static global::System.Linq.Expressions.Expression<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, bool, global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto>> _ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order_P1_bool_Expression() 
        {
            var p_o = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order), "o");
            var p_lightweight = global::System.Linq.Expressions.Expression.Parameter(typeof(bool), "lightweight");
            var expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null));
            var expr_1 = global::System.Linq.Expressions.Expression.Property(p_o, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // o.Id
            var expr_3 = global::System.Linq.Expressions.Expression.Property(p_o, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order).GetProperty("Items", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // o.Items
            var expr_2 = global::System.Linq.Expressions.Expression.Call(global::System.Linq.Enumerable.First(global::System.Linq.Enumerable.Where(typeof(global::System.Linq.Enumerable).GetMethods(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static), m => m.Name == "Count" && m.IsGenericMethodDefinition && m.GetGenericArguments().Length == 1 && m.GetParameters().Length == 1 && m.GetParameters()[0].ParameterType.IsGenericType && !m.GetParameters()[0].ParameterType.IsGenericParameter)).MakeGenericMethod(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.LineItem)), new global::System.Linq.Expressions.Expression[] { expr_3 });
            var expr_5 = global::System.Linq.Expressions.Expression.Constant(null, typeof(object)); // null
            var expr_4 = global::System.Linq.Expressions.Expression.Convert(expr_5, typeof(string));
            var expr_6 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_1);
            var expr_7 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetProperty("ItemCount", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_2);
            var expr_8 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetProperty("CustomerName", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_4);
            var expr_9 = global::System.Linq.Expressions.Expression.MemberInit(expr_0, expr_6, expr_7, expr_8);
            return global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, bool, global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto>>(expr_9, p_o, p_lightweight);
        }
    }
}


// === ExpressiveSharp_Docs_Playground_Snippet_OrderDto.Attributes.g.cs ===
// <auto-generated/>

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    static partial class ExpressiveSharp_Docs_Playground_Snippet_OrderDto { }
}


// === ExpressionRegistry.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Reflection;

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    internal static class ExpressionRegistry
    {
        private static Dictionary<nint, LambdaExpression> Build()
        {
            const BindingFlags allFlags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static;
            var map = new Dictionary<nint, LambdaExpression>();
            
            Register(map, typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetConstructor(allFlags, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order) }, null), "ExpressiveSharp.Generated.ExpressiveSharp_Docs_Playground_Snippet_OrderDto", "_ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order_Expression");
            Register(map, typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetConstructor(allFlags, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order), typeof(bool) }, null), "ExpressiveSharp.Generated.ExpressiveSharp_Docs_Playground_Snippet_OrderDto", "_ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Order_P1_bool_Expression");
            
            return map;
        }
        
        private static volatile Dictionary<nint, LambdaExpression> _map = Build();
        
        internal static void ResetMap() => _map = Build();
        
        public static LambdaExpression TryGet(MemberInfo member)
        {
            var handle = member switch
            {
                MethodInfo m      => (nint?)m.MethodHandle.Value,
                PropertyInfo p    => p.GetMethod?.MethodHandle.Value,
                ConstructorInfo c => (nint?)c.MethodHandle.Value,
                _                 => null
            };
            
            return handle.HasValue && _map.TryGetValue(handle.Value, out var expr) ? expr : null;
        }
        
        private static void Register(Dictionary<nint, LambdaExpression> map, MethodBase m, string exprClass, string exprMethodName)
        {
            if (m is null) return;
            var exprType = m.DeclaringType?.Assembly.GetType(exprClass) ?? typeof(ExpressionRegistry).Assembly.GetType(exprClass);
            var exprMethod = exprType?.GetMethod(exprMethodName, BindingFlags.Static | BindingFlags.NonPublic);
            if (exprMethod is null) return;
            var expr = (LambdaExpression)exprMethod.Invoke(null, null)!;
            
            // Apply declared transformers from the generated class (if any)
            const string expressionSuffix = "_Expression";
            if (exprMethodName.EndsWith(expressionSuffix, StringComparison.Ordinal))
            {
                var transformersSuffix = exprMethodName.Substring(0, exprMethodName.Length - expressionSuffix.Length) + "_Transformers";
                var transformersMethod = exprType.GetMethod(transformersSuffix, BindingFlags.Static | BindingFlags.NonPublic);
                if (transformersMethod?.Invoke(null, null) is global::ExpressiveSharp.IExpressionTreeTransformer[] transformers)
                {
                    Expression transformed = expr;
                    foreach (var t in transformers) transformed = t.Transform(transformed);
                    if (transformed is LambdaExpression lambdaResult) expr = lambdaResult;
                }
            }
            
            map[m.MethodHandle.Value] = expr;
        }
    }
}


// === PolyfillInterceptors_b1293e61.g.cs ===
// <auto-generated/>
#nullable disable

namespace ExpressiveSharp.Generated.Interceptors
{
    internal static partial class PolyfillInterceptors
    {
        [global::System.Runtime.CompilerServices.InterceptsLocationAttribute(1, "S8urpwqxcEqJKhipCB9DPn8BAABfX1NuaXBwZXQuY3M=")]
        internal static global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto> __Polyfill_Select_3e61_14_21(
            this global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order> source,
            global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto> __func)
        {
            // Source: o => new OrderDto(o, true)
            var i3e6114c21_p_o = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order), "o");
            var i3e6114c21_expr_1 = global::System.Linq.Expressions.Expression.Constant(true, typeof(bool)); // true
            var i3e6114c21_expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order), typeof(bool) }, null), i3e6114c21_p_o, i3e6114c21_expr_1);
            var __lambda = global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order, global::ExpressiveSharp.Docs.Playground.Snippet.OrderDto>>(i3e6114c21_expr_0, i3e6114c21_p_o);
            return global::ExpressiveSharp.ExpressiveQueryableExtensions.AsExpressive(
                global::System.Linq.Queryable.Select(
                    (global::System.Linq.IQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Order>)source,
                    __lambda));
        }
    }
}

namespace System.Runtime.CompilerServices
{
    [global::System.AttributeUsage(global::System.AttributeTargets.Method, AllowMultiple = true)]
    file sealed class InterceptsLocationAttribute : global::System.Attribute
    {
        public InterceptsLocationAttribute(int version, string data) { }
    }
}

Open in Playground →

db
    .Orders
    .Select(o => new OrderDto(o, true))

// Setup
public class OrderDto
{
    public int Id { get; set; }
    public int ItemCount { get; set; }
    public string? CustomerName { get; set; }

    public OrderDto() { }

    [Expressive]
    public OrderDto(Order o)
    {
        Id = o.Id;
        ItemCount = o.Items.Count();
        CustomerName = o.Customer.Name;
    }

    [Expressive]
    public OrderDto(Order o, bool lightweight)
    {
        Id = o.Id;
        ItemCount = o.Items.Count();
        CustomerName = null;
    }
}

Generated SQL:

SELECT "o"."Id", (
    SELECT COUNT(*)
    FROM "LineItems" AS "l"
    WHERE "o"."Id" = "l"."OrderId") AS "ItemCount", NULL AS "CustomerName"
FROM "Orders" AS "o"

Using Switch Expressions in Constructors

Constructor bodies support the same modern C# syntax as other [Expressive] members:

C#

db
    .Products
    .Select(p => new ProductDto(p))

// Setup
public class ProductDto
{
    public int Id { get; set; }
    public string Name { get; set; } = "";
    public decimal Price { get; set; }
    public string PriceTier { get; set; } = "";

    public ProductDto() { }

    [Expressive]
    public ProductDto(Product p)
    {
        Id = p.Id;
        Name = p.Name;
        Price = p.ListPrice;
        PriceTier = p.ListPrice switch
        {
            > 500m => "Premium",
            > 100m => "Standard",
            _      => "Budget"
        };
    }
}

SELECT "p"."Id", "p"."Name", "p"."ListPrice" AS "Price", CASE
    WHEN ef_compare("p"."ListPrice", '500.0') > 0 THEN 'Premium'
    WHEN ef_compare("p"."ListPrice", '100.0') > 0 THEN 'Standard'
    ELSE 'Budget'
END AS "PriceTier"
FROM "Products" AS "p"

SELECT p."Id", p."Name", p."ListPrice" AS "Price", CASE
    WHEN p."ListPrice" > 500.0 THEN 'Premium'
    WHEN p."ListPrice" > 100.0 THEN 'Standard'
    ELSE 'Budget'
END AS "PriceTier"
FROM "Products" AS p

SELECT [p].[Id], [p].[Name], [p].[ListPrice] AS [Price], CASE
    WHEN [p].[ListPrice] > 500.0 THEN N'Premium'
    WHEN [p].[ListPrice] > 100.0 THEN N'Standard'
    ELSE N'Budget'
END AS [PriceTier]
FROM [Products] AS [p]

playground.products.Aggregate([
    {
         "$project" : {
             "_id" : "$_id",
            "Name" : "$Name",
            "Price" : "$ListPrice",
            "PriceTier" : {
                 "$cond" : {
                     "if" : {
                         "$gt" : [
                            "$ListPrice",
                            { "$numberDecimal" : "500" }
                        ] 
                    },
                    "then" : "Premium",
                    "else" : {
                         "$cond" : {
                             "if" : {
                                 "$gt" : [
                                    "$ListPrice",
                                    { "$numberDecimal" : "100" }
                                ] 
                            },
                            "then" : "Standard",
                            "else" : "Budget" 
                        } 
                    } 
                } 
            } 
        } 
    }
])

// === ExpressiveSharp_Docs_Playground_Snippet_ProductDto._ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Product.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Linq;
using System.Linq.Expressions;
using ExpressiveSharp;
using ExpressiveSharp.EntityFrameworkCore;
using ExpressiveSharp.Docs.PlaygroundModel.Webshop;
using ExpressiveSharp.Docs.Playground.Snippet;

namespace ExpressiveSharp.Generated
{
    static partial class ExpressiveSharp_Docs_Playground_Snippet_ProductDto 
    {
        // [Expressive]
        // public ProductDto(Product p)
        // {
        //     Id = p.Id;
        //     Name = p.Name;
        //     Price = p.ListPrice;
        //     PriceTier = p.ListPrice switch
        //     {
        //         > 500m => "Premium",
        //         > 100m => "Standard",
        //         _ => "Budget"
        //     };
        // }
        static global::System.Linq.Expressions.Expression<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product, global::ExpressiveSharp.Docs.Playground.Snippet.ProductDto>> _ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Product_Expression() 
        {
            var p_p = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product), "p");
            var expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.ProductDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null));
            var expr_1 = global::System.Linq.Expressions.Expression.Property(p_p, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // p.Id
            var expr_2 = global::System.Linq.Expressions.Expression.Property(p_p, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product).GetProperty("Name", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // p.Name
            var expr_3 = global::System.Linq.Expressions.Expression.Property(p_p, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product).GetProperty("ListPrice", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // p.ListPrice
            var expr_4 = global::System.Linq.Expressions.Expression.Property(p_p, typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product).GetProperty("ListPrice", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // p.ListPrice
            var expr_5 = global::System.Linq.Expressions.Expression.Constant("Budget", typeof(string)); // "Budget"
            var expr_7 = global::System.Linq.Expressions.Expression.Constant(100m, typeof(decimal)); // 100m
            var expr_6 = global::System.Linq.Expressions.Expression.MakeBinary(global::System.Linq.Expressions.ExpressionType.GreaterThan, expr_4, expr_7);
            var expr_8 = global::System.Linq.Expressions.Expression.Constant("Standard", typeof(string)); // "Standard"
            var expr_9 = global::System.Linq.Expressions.Expression.Condition(expr_6, expr_8, expr_5, typeof(string));
            var expr_11 = global::System.Linq.Expressions.Expression.Constant(500m, typeof(decimal)); // 500m
            var expr_10 = global::System.Linq.Expressions.Expression.MakeBinary(global::System.Linq.Expressions.ExpressionType.GreaterThan, expr_4, expr_11);
            var expr_12 = global::System.Linq.Expressions.Expression.Constant("Premium", typeof(string)); // "Premium"
            var expr_13 = global::System.Linq.Expressions.Expression.Condition(expr_10, expr_12, expr_9, typeof(string));
            var expr_14 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.ProductDto).GetProperty("Id", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_1);
            var expr_15 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.ProductDto).GetProperty("Name", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_2);
            var expr_16 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.ProductDto).GetProperty("Price", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_3);
            var expr_17 = global::System.Linq.Expressions.Expression.Bind(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.ProductDto).GetProperty("PriceTier", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_13);
            var expr_18 = global::System.Linq.Expressions.Expression.MemberInit(expr_0, expr_14, expr_15, expr_16, expr_17);
            return global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product, global::ExpressiveSharp.Docs.Playground.Snippet.ProductDto>>(expr_18, p_p);
        }
    }
}


// === ExpressiveSharp_Docs_Playground_Snippet_ProductDto.Attributes.g.cs ===
// <auto-generated/>

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    static partial class ExpressiveSharp_Docs_Playground_Snippet_ProductDto { }
}


// === ExpressionRegistry.g.cs ===
// <auto-generated/>
#nullable disable

using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Reflection;

namespace ExpressiveSharp.Generated
{
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    internal static class ExpressionRegistry
    {
        private static Dictionary<nint, LambdaExpression> Build()
        {
            const BindingFlags allFlags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static;
            var map = new Dictionary<nint, LambdaExpression>();
            
            Register(map, typeof(global::ExpressiveSharp.Docs.Playground.Snippet.ProductDto).GetConstructor(allFlags, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product) }, null), "ExpressiveSharp.Generated.ExpressiveSharp_Docs_Playground_Snippet_ProductDto", "_ctor_P0_ExpressiveSharp_Docs_PlaygroundModel_Webshop_Product_Expression");
            
            return map;
        }
        
        private static volatile Dictionary<nint, LambdaExpression> _map = Build();
        
        internal static void ResetMap() => _map = Build();
        
        public static LambdaExpression TryGet(MemberInfo member)
        {
            var handle = member switch
            {
                MethodInfo m      => (nint?)m.MethodHandle.Value,
                PropertyInfo p    => p.GetMethod?.MethodHandle.Value,
                ConstructorInfo c => (nint?)c.MethodHandle.Value,
                _                 => null
            };
            
            return handle.HasValue && _map.TryGetValue(handle.Value, out var expr) ? expr : null;
        }
        
        private static void Register(Dictionary<nint, LambdaExpression> map, MethodBase m, string exprClass, string exprMethodName)
        {
            if (m is null) return;
            var exprType = m.DeclaringType?.Assembly.GetType(exprClass) ?? typeof(ExpressionRegistry).Assembly.GetType(exprClass);
            var exprMethod = exprType?.GetMethod(exprMethodName, BindingFlags.Static | BindingFlags.NonPublic);
            if (exprMethod is null) return;
            var expr = (LambdaExpression)exprMethod.Invoke(null, null)!;
            
            // Apply declared transformers from the generated class (if any)
            const string expressionSuffix = "_Expression";
            if (exprMethodName.EndsWith(expressionSuffix, StringComparison.Ordinal))
            {
                var transformersSuffix = exprMethodName.Substring(0, exprMethodName.Length - expressionSuffix.Length) + "_Transformers";
                var transformersMethod = exprType.GetMethod(transformersSuffix, BindingFlags.Static | BindingFlags.NonPublic);
                if (transformersMethod?.Invoke(null, null) is global::ExpressiveSharp.IExpressionTreeTransformer[] transformers)
                {
                    Expression transformed = expr;
                    foreach (var t in transformers) transformed = t.Transform(transformed);
                    if (transformed is LambdaExpression lambdaResult) expr = lambdaResult;
                }
            }
            
            map[m.MethodHandle.Value] = expr;
        }
    }
}


// === PolyfillInterceptors_b1293e61.g.cs ===
// <auto-generated/>
#nullable disable

namespace ExpressiveSharp.Generated.Interceptors
{
    internal static partial class PolyfillInterceptors
    {
        [global::System.Runtime.CompilerServices.InterceptsLocationAttribute(1, "LOtA3ssvVKb9OKV6nEuw24EBAABfX1NuaXBwZXQuY3M=")]
        internal static global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.Playground.Snippet.ProductDto> __Polyfill_Select_3e61_14_23(
            this global::ExpressiveSharp.IExpressiveQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product> source,
            global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product, global::ExpressiveSharp.Docs.Playground.Snippet.ProductDto> __func)
        {
            // Source: p => new ProductDto(p)
            var i3e6114c23_p_p = global::System.Linq.Expressions.Expression.Parameter(typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product), "p");
            var i3e6114c23_expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::ExpressiveSharp.Docs.Playground.Snippet.ProductDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] { typeof(global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product) }, null), i3e6114c23_p_p); // new ProductDto(p)
            var __lambda = global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product, global::ExpressiveSharp.Docs.Playground.Snippet.ProductDto>>(i3e6114c23_expr_0, i3e6114c23_p_p);
            return global::ExpressiveSharp.ExpressiveQueryableExtensions.AsExpressive(
                global::System.Linq.Queryable.Select(
                    (global::System.Linq.IQueryable<global::ExpressiveSharp.Docs.PlaygroundModel.Webshop.Product>)source,
                    __lambda));
        }
    }
}

namespace System.Runtime.CompilerServices
{
    [global::System.AttributeUsage(global::System.AttributeTargets.Method, AllowMultiple = true)]
    file sealed class InterceptsLocationAttribute : global::System.Attribute
    {
        public InterceptsLocationAttribute(int version, string data) { }
    }
}

Open in Playground →

db
    .Products
    .Select(p => new ProductDto(p))

// Setup
public class ProductDto
{
    public int Id { get; set; }
    public string Name { get; set; } = "";
    public decimal Price { get; set; }
    public string PriceTier { get; set; } = "";

    public ProductDto() { }

    [Expressive]
    public ProductDto(Product p)
    {
        Id = p.Id;
        Name = p.Name;
        Price = p.ListPrice;
        PriceTier = p.ListPrice switch
        {
            > 500m => "Premium",
            > 100m => "Standard",
            _      => "Budget"
        };
    }
}

Generated SQL:

SELECT "p"."Id", "p"."Name", "p"."ListPrice" AS "Price", CASE
    WHEN ef_compare("p"."ListPrice", '500.0') > 0 THEN 'Premium'
    WHEN ef_compare("p"."ListPrice", '100.0') > 0 THEN 'Standard'
    ELSE 'Budget'
END AS "PriceTier"
FROM "Products" AS "p"

Using [ExpressiveForConstructor] for External Types

If you do not own the DTO type (third-party library, shared package), use [ExpressiveForConstructor] to provide the expression body externally:

using ExpressiveSharp.Mapping;

[ExpressiveForConstructor(typeof(ExternalOrderDto))]
static ExternalOrderDto CreateDto(int id, string name)
    => new ExternalOrderDto { Id = id, Name = name };

See External Member Mapping for details.

Tips

Always add a parameterless constructor

The generator emits new T() { ... } syntax. If the parameterless constructor is missing, the build will fail.

Keep mappings pure

No side effects, no calls to non-expressible methods. Everything in the constructor body must be translatable to SQL.

INFO

Constructor bodies are block-bodied by nature, but they do not require AllowBlockBody = true — the generator handles them automatically. UseExpressives() registers the FlattenBlockExpressions transformer to flatten them for EF Core.

See Also

• Computed Entity Properties -- reusable computed values referenced in constructor projections
• External Member Mapping -- [ExpressiveForConstructor] for types you do not own
• Scoring and Classification -- switch expressions and pattern matching in projections