Checkpoint (still hacking about)

samples/BasicSample/BasicSample.csproj

@@ -10,6 +10,8 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="5.0.6" />
+    <PackageReference Include="Microsoft.Extensions.Logging" Version="5.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Console" Version="5.0.0" />
   </ItemGroup>
 
   <ItemGroup>

samples/BasicSample/Program.cs

@@ -4,9 +4,11 @@ using Microsoft.Data.Sqlite;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Caching.Memory;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations.Schema;
 using System.Diagnostics;
 using System.Linq;
 
@@ -26,6 +28,14 @@ namespace BasicSample
 
         [Projectable]
         public double TotalSpent => Orders.Sum(x => x.PriceSum);
+
+        [Projectable]
+        public Order MostValuableOrder
+            => Orders.OrderByDescending(x => x.PriceSum).FirstOrDefault();
+
+        [Projectable]
+        public IEnumerable<Product> FindOrderedProducts(string namePrefix)
+            => Orders.SelectMany(x => x.Items).Select(x => x.Product).Where(x => x.Name.StartsWith(namePrefix));
     }
 
     public class Product
@@ -85,7 +95,8 @@ namespace BasicSample
                 .AddDbContext<ApplicationDbContext>(options => {
                     options
                         .UseSqlite(dbConnection)
-                        .UseProjections();
+                        .UseProjections()
+                        .UseLoggerFactory(LoggerFactory.Create(builder => builder.AddConsole()));
                 })
                 .BuildServiceProvider();
 
@@ -119,6 +130,8 @@ namespace BasicSample
             dbContext.Users.Add(user);
             dbContext.SaveChanges();
 
+            // What did our user spent in total
+            {
                 var query = dbContext.Users
                     .Select(x => new {
                         Name = x.FullName,
@@ -127,9 +140,33 @@ namespace BasicSample
 
                 var result = query.FirstOrDefault();
 
-            Console.WriteLine($"Our user {result.Name} spent {result.TotalSpent}");
-            Console.WriteLine($"We used the following query:");
-            Console.WriteLine(query.ToQueryString());
+                Console.WriteLine($"Our user ({result.Name}) spent {result.TotalSpent}");
+            }
+
+            {
+                var query = dbContext.Users
+                    .Select(x => new {
+                        Name = x.FullName,
+                        x.MostValuableOrder
+                    });
+
+                var result = query.FirstOrDefault();
+
+                Console.WriteLine($"Our users spent {result.MostValuableOrder.PriceSum} on its biggest order");
+            }
+
+            {
+                var query = dbContext.Users
+                    .Select(x => new {
+                        Name = x.FullName,
+                        Ordered = x.FindOrderedProducts("Red").Select(x => x.Name)
+                    });
+
+                var result = query.FirstOrDefault();
+
+                Console.WriteLine($"Our users bought the following products starting with 'Red': {string.Join(", ", result.Ordered)}");
+            }
+
         }
     }
 }

src/EntityFrameworkCore.Projections.Generator/ExpressionSyntaxRewriter.cs

@@ -9,6 +9,7 @@ using System.Threading.Tasks;
 
 namespace EntityFrameworkCore.Projections.Generator
 {
+
     public class ExpressionSyntaxRewriter : CSharpSyntaxRewriter
     {
         readonly INamedTypeSymbol _targetTypeSymbol;

src/EntityFrameworkCore.Projections.Generator/ParameterSyntaxRewriter.cs

@@ -0,0 +1,41 @@
+using System.Linq;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+
+namespace EntityFrameworkCore.Projections.Generator
+{
+    public class ParameterSyntaxRewriter : CSharpSyntaxRewriter
+    {
+        readonly SemanticModel _semanticModel;
+
+        public ParameterSyntaxRewriter(SemanticModel semanticModel)
+        {
+            _semanticModel = semanticModel;
+        }
+
+        public override SyntaxNode? VisitQualifiedName(QualifiedNameSyntax node)
+        {
+            // todo: Fully qualify these
+            return node;
+        }
+
+        public override SyntaxNode? VisitParameter(ParameterSyntax node)
+        {
+            var symbol = _semanticModel.GetDeclaredSymbol(node);
+
+            if (symbol is not null)
+            {
+            }
+
+            var thisKeywordIndex = node.Modifiers.IndexOf(SyntaxKind.ThisKeyword);
+            if (thisKeywordIndex != -1)
+            {
+                node = node.WithModifiers(node.Modifiers.RemoveAt(thisKeywordIndex));
+            }
+
+
+            return node;
+        }
+    }
+}

src/EntityFrameworkCore.Projections.Generator/ProjectableDescriptor.cs

@@ -15,6 +15,10 @@ namespace EntityFrameworkCore.Projections.Generator
 
         public IEnumerable<string> NestedInClassNames { get; set; }
 
+        public string TargetClassNamespace { get; set; }
+
+        public IEnumerable<string> TargetNestedInClassNames { get; set; }
+
         public string ClassName { get; set; }
 
         public string MemberName { get; set; }

src/EntityFrameworkCore.Projections.Generator/ProjectableInterpreter.cs

@@ -1,17 +1,14 @@
-using Microsoft.CodeAnalysis;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 
 namespace EntityFrameworkCore.Projections.Generator
 {
     public static class ProjectableInterpreter
     {
-        static IEnumerable<string> GetNestedInClassPath(INamedTypeSymbol namedTypeSymbol)
+        static IEnumerable<string> GetNestedInClassPath(ITypeSymbol namedTypeSymbol)
         {
             if (namedTypeSymbol.ContainingType is not null)
             {
@@ -34,6 +31,7 @@ namespace EntityFrameworkCore.Projections.Generator
                 return null;
             }
 
+
             var projectableAttributeTypeSymbol = context.Compilation.GetTypeByMetadataName("EntityFrameworkCore.Projections.ProjectableAttribute");
 
             var projectableAttributeClass = memberSymbol.GetAttributes()
@@ -46,20 +44,32 @@ namespace EntityFrameworkCore.Projections.Generator
             }
 
             var expressionSyntaxRewriter = new ExpressionSyntaxRewriter(memberSymbol.ContainingType, semanticModel);
+            var parameterSyntaxRewriter = new ParameterSyntaxRewriter(semanticModel);
 
-            var descriptor = new ProjectableDescriptor
-            {
+            var descriptor = new ProjectableDescriptor {
                 ClassName = memberSymbol.ContainingType.Name,
                 ClassNamespace = memberSymbol.ContainingType.ContainingNamespace.IsGlobalNamespace ? null : memberSymbol.ContainingType.ContainingNamespace.ToDisplayString(),
                 MemberName = memberSymbol.Name,
                 NestedInClassNames = GetNestedInClassPath(memberSymbol.ContainingType)
             };
 
+            if (memberSymbol is IMethodSymbol methodSymbol && methodSymbol.IsExtensionMethod)
+            {
+                var targetTypeSymbol = methodSymbol.Parameters.First().Type;
+                descriptor.TargetClassNamespace = targetTypeSymbol.ContainingNamespace.IsGlobalNamespace ? null : targetTypeSymbol.ContainingNamespace.ToDisplayString();
+                descriptor.TargetNestedInClassNames = GetNestedInClassPath(targetTypeSymbol);
+            }
+            else
+            {
+                descriptor.TargetClassNamespace = descriptor.ClassNamespace;
+                descriptor.TargetNestedInClassNames = descriptor.NestedInClassNames;
+            }
+
             if (memberDeclarationSyntax is MethodDeclarationSyntax methodDeclarationSyntax)
             {
                 descriptor.ReturnTypeName = methodDeclarationSyntax.ReturnType.ToString();
                 descriptor.Body = expressionSyntaxRewriter.Visit(methodDeclarationSyntax.ExpressionBody.Expression);
-                descriptor.ParametersListString = methodDeclarationSyntax.ParameterList.ToString();
+                descriptor.ParametersListString = parameterSyntaxRewriter.Visit(methodDeclarationSyntax.ParameterList).ToString();
             }
             else if (memberDeclarationSyntax is PropertyDeclarationSyntax propertyDeclarationSyntax)
             {

src/EntityFrameworkCore.Projections.Generator/ProjectionExpressionGenerator.cs

@@ -38,6 +38,16 @@ namespace EntityFrameworkCore.Projections.Generator
                         resultBuilder.AppendLine(usingDirective);
                     }
 
+                    if (projectable.TargetClassNamespace is not null && !projectable.UsingDirectives.Contains(projectable.TargetClassNamespace))
+                    {
+                        resultBuilder.AppendLine($"using {projectable.TargetClassNamespace};");
+                    }
+
+                    if (projectable.ClassNamespace is not null && projectable.ClassNamespace != projectable.TargetClassNamespace && !projectable.UsingDirectives.Contains(projectable.ClassNamespace))
+                    {
+                        resultBuilder.AppendLine($"using {projectable.ClassNamespace};");
+                    }
+
                     var generatedClassName = ProjectionExpressionClassNameGenerator.GenerateName(projectable.ClassNamespace, projectable.NestedInClassNames, projectable.MemberName);
 
                     resultBuilder.Append($@"
@@ -46,7 +56,7 @@ namespace EntityFrameworkCore.Projections.Generated
 {{
     public static class {generatedClassName}
     {{
-        public static System.Linq.Expressions.Expression<System.Func<{projectable.ClassNamespace}.{string.Join(".", projectable.NestedInClassNames)}, {projectable.ReturnTypeName}>> Expression{projectable.ParametersListString} => 
+        public static System.Linq.Expressions.Expression<System.Func<{projectable.TargetClassNamespace}.{string.Join(".", projectable.TargetNestedInClassNames)}, {projectable.ReturnTypeName}>> Expression{projectable.ParametersListString} => 
             {ProjectionTargetParameterName} => {projectable.Body};
     }}
 }}");

src/EntityFrameworkCore.Projections/Infrastructure/Internal/ProjectionOptionsExtension.cs

@@ -1,5 +1,6 @@
 using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Query;
+using Microsoft.EntityFrameworkCore.Query.Internal;
 using Microsoft.Extensions.DependencyInjection;
 using System;
 using System.Collections.Generic;
@@ -18,25 +19,24 @@ namespace EntityFrameworkCore.Projections.Infrastructure.Internal
 
         public DbContextOptionsExtensionInfo Info { get; }
 
+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Usage", "EF1001:Internal EF Core API usage.", Justification = "Needed")]
         public void ApplyServices(IServiceCollection services)
         {
-            var existingPreprocessorFactoryRegistration = services.FirstOrDefault(x => x.ServiceType == typeof(IQueryTranslationPreprocessorFactory));
-
-            if (existingPreprocessorFactoryRegistration?.ImplementationType is null)
+            var queryCompilerRegistration = services.FirstOrDefault(x => x.ServiceType == typeof(IQueryCompiler));
+            if (queryCompilerRegistration?.ImplementationType is null)
             {
-                throw new InvalidOperationException("Expected a QueryTranslationPreprocessor to be registered. Please make sure to register your database provider first");
+                throw new InvalidOperationException("No queryCompiler is configured yet. Please make sure to configure a database provider first"); ;
             }
 
-            // Ensure that we can still resolve this factory
-            services.Add(new ServiceDescriptor(existingPreprocessorFactoryRegistration.ImplementationType, existingPreprocessorFactoryRegistration.ImplementationType, existingPreprocessorFactoryRegistration.Lifetime));
-            services.Remove(existingPreprocessorFactoryRegistration);
+            // Ensure that we can still resolve this queryCompiler
+            services.Add(new ServiceDescriptor(queryCompilerRegistration.ImplementationType, queryCompilerRegistration.ImplementationType, queryCompilerRegistration.Lifetime));
+            services.Remove(queryCompilerRegistration);
 
             services.Add(new ServiceDescriptor(
-                typeof(IQueryTranslationPreprocessorFactory),
-                serviceProvider => new WrappedQueryTranslationPreprocessorFactory((IQueryTranslationPreprocessorFactory)serviceProvider.GetRequiredService(existingPreprocessorFactoryRegistration.ImplementationType), serviceProvider.GetRequiredService<QueryTranslationPreprocessorDependencies>()),
-                existingPreprocessorFactoryRegistration.Lifetime
+                typeof(IQueryCompiler),
+                serviceProvider => new WrappedQueryCompiler((IQueryCompiler)serviceProvider.GetRequiredService(queryCompilerRegistration.ImplementationType)),
+                queryCompilerRegistration.Lifetime
             ));
-
         }
 
         public void Validate(IDbContextOptions options)

src/EntityFrameworkCore.Projections/Infrastructure/Internal/WrappedQueryCompiler.cs

@@ -0,0 +1,41 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using EntityFrameworkCore.Projections.Services;
+using Microsoft.EntityFrameworkCore.Query;
+using Microsoft.EntityFrameworkCore.Query.Internal;
+
+namespace EntityFrameworkCore.Projections.Infrastructure.Internal
+{
+    [System.Diagnostics.CodeAnalysis.SuppressMessage("Usage", "EF1001:Internal EF Core API usage.", Justification = "Needed")]
+    public sealed class WrappedQueryCompiler : IQueryCompiler
+    {
+        readonly ProjectableExpressionReplacer _projectionExpressionReplacer = new();
+        readonly IQueryCompiler _queryCompiler;
+
+        public WrappedQueryCompiler(IQueryCompiler queryCompiler)
+        {
+            _queryCompiler = queryCompiler;
+        }
+
+        public Func<QueryContext, TResult> CreateCompiledAsyncQuery<TResult>(Expression query)
+            => _queryCompiler.CreateCompiledAsyncQuery<TResult>(PatchQuery(query));
+
+        public Func<QueryContext, TResult> CreateCompiledQuery<TResult>(Expression query)
+            => _queryCompiler.CreateCompiledQuery<TResult>(PatchQuery(query));
+
+        public TResult Execute<TResult>(Expression query)
+            => _queryCompiler.Execute<TResult>(PatchQuery(query));
+
+        public TResult ExecuteAsync<TResult>(Expression query, CancellationToken cancellationToken)
+            => _queryCompiler.ExecuteAsync<TResult>(PatchQuery(query), cancellationToken);
+
+        Expression PatchQuery(Expression expression)
+            => _projectionExpressionReplacer.Visit(expression);
+        
+    }
+}

src/EntityFrameworkCore.Projections/Infrastructure/Internal/WrappedQueryTranslationPreprocessorFactory.cs

@@ -1,54 +0,0 @@
-using EntityFrameworkCore.Projections.Services;
-using Microsoft.EntityFrameworkCore.Query;
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Linq.Expressions;
-using System.Text;
-using System.Threading.Tasks;
-
-namespace EntityFrameworkCore.Projections.Infrastructure.Internal
-{
-    public class WrappedQueryTranslationPreprocessorFactory : IQueryTranslationPreprocessorFactory
-    {
-        readonly IQueryTranslationPreprocessorFactory _originalFactory;
-        readonly QueryTranslationPreprocessorDependencies _dependencies;
-
-        public WrappedQueryTranslationPreprocessorFactory(IQueryTranslationPreprocessorFactory originalFactory, QueryTranslationPreprocessorDependencies dependencies)
-        {
-            _originalFactory = originalFactory;
-            _dependencies = dependencies;
-        }
-
-        public QueryTranslationPreprocessor Create(QueryCompilationContext queryCompilationContext)
-        {
-            var originalPreprocessor = _originalFactory.Create(queryCompilationContext);
-
-            return new WrappedQueryTranslationPreprocessor(originalPreprocessor, _dependencies, queryCompilationContext);
-        }
-    }
-
-    public class WrappedQueryTranslationPreprocessor : QueryTranslationPreprocessor
-    {
-        readonly ProjectableExpressionReplacer _projectableExpressionReplacer;
-        readonly QueryTranslationPreprocessor _originalPreprocessor;
-
-        public WrappedQueryTranslationPreprocessor(QueryTranslationPreprocessor originalPreprocessor, QueryTranslationPreprocessorDependencies dependencies, QueryCompilationContext queryCompilationContext) : base(dependencies, queryCompilationContext)
-        {
-            _originalPreprocessor = originalPreprocessor;
-            _projectableExpressionReplacer = new ProjectableExpressionReplacer();
-        }
-
-        public override Expression NormalizeQueryableMethod(Expression expression)
-        {
-            return _originalPreprocessor.NormalizeQueryableMethod(expression);
-        }
-
-        public override Expression Process(Expression query)
-        {
-            query = _projectableExpressionReplacer.Visit(query);
-
-            return _originalPreprocessor.Process(query);
-        }
-    }
-}

src/EntityFrameworkCore.Projections/Services/ParameterExtractor.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace EntityFrameworkCore.Projections.Services
+{
+    public sealed class ParameterExtractor : ExpressionVisitor
+    {
+        List<ParameterExpression>? _extractedParameters = null;
+
+        protected override Expression VisitParameter(ParameterExpression node)
+        {
+            if (_extractedParameters is null)
+            {
+                _extractedParameters = new List<ParameterExpression>();
+            }
+
+            _extractedParameters.Add(node);
+            return base.VisitParameter(node);
+        }
+
+        public IEnumerable<ParameterExpression> ExtractedParameters
+            => _extractedParameters ?? Enumerable.Empty<ParameterExpression>();
+    }
+}

src/EntityFrameworkCore.Projections/Services/ProjectionExpressionResolver.cs

@@ -43,17 +43,22 @@ namespace EntityFrameworkCore.Projections.Services
                     }
                     else
                     {
-                        var test1 = argumentExpressions.Cast<ParameterExpression>()!;
+                        var parameterExtractor = new ParameterExtractor();
+                        foreach (var argument in argumentExpressions)
+                        {
+                            parameterExtractor.Visit(argument);
+                        }
 
-                        var expressionFactoryConstructionMethod =
-                            Expression.Lambda<Func<LambdaExpression>>(
+                        var lambda = Expression.Lambda<Func<LambdaExpression>>(
                                 Expression.Call(
                                     expressionFactoryMethod,
                                     argumentExpressions
-                                )
-                            ).Compile();
+                                ),
+                                parameterExtractor.ExtractedParameters
+                            );
 
-                        return expressionFactoryConstructionMethod.Invoke();
+
+                        return lambda.Compile().Invoke();
                     }
                 });
             }); 

tests/EntityFrameworkCore.Projections.FunctionalTests/ExtensionsMethods/Entity.cs

@@ -0,0 +1,11 @@
+namespace EntityFrameworkCore.Projections.FunctionalTests.ExtensionMethods
+{
+
+    public partial class ExtensionMethodTests
+    {
+        public class Entity
+        {
+            public int Id { get; set; }
+        }    
+    }
+}

tests/EntityFrameworkCore.Projections.FunctionalTests/ExtensionsMethods/EntityExtensions.cs

@@ -0,0 +1,8 @@
+namespace EntityFrameworkCore.Projections.FunctionalTests.ExtensionMethods
+{
+    public static class EntityExtensions
+    {
+        [Projectable]
+        public static int Foo(this ExtensionMethodTests.Entity entity) => entity.Id + 1;
+    }
+}

tests/EntityFrameworkCore.Projections.FunctionalTests/ExtensionsMethods/ExtensionMethodTests.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using EntityFrameworkCore.Projections.FunctionalTests.Helpers;
+using Microsoft.EntityFrameworkCore;
+using ScenarioTests;
+using Xunit;
+
+namespace EntityFrameworkCore.Projections.FunctionalTests.ExtensionMethods
+{
+
+    public partial class ExtensionMethodTests
+    {
+        [Scenario(NamingPolicy = ScenarioTestMethodNamingPolicy.Test)]
+        public void PlayScenario(ScenarioContext scenario)
+        {
+            using var dbContext = new SampleDbContext<Entity>();
+
+            scenario.Fact("We can select on a projectable extension method", () => {
+                const string expectedQueryString = "SELECT [e].[Id]\r\nFROM [Entity] AS [e]";
+
+                var query = dbContext.Set<Entity>()
+                    .Select(x => x.Foo());
+
+                Assert.Equal(expectedQueryString, query.ToQueryString());
+            });
+
+        }
+    }
+}

tests/EntityFrameworkCore.Projections.FunctionalTests/StatefullComplexFunctionTests.cs

@@ -0,0 +1,74 @@
+using System;
+using System.Collections.Generic;
+using System.Data.SqlTypes;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using EntityFrameworkCore.Projections.FunctionalTests.Helpers;
+using EntityFrameworkCore.Projections.Services;
+using Microsoft.EntityFrameworkCore;
+using ScenarioTests;
+using Xunit;
+
+namespace EntityFrameworkCore.Projections.FunctionalTests
+{
+    public partial class StatefullComplexFunctionTests
+    {
+        public record Entity
+        {
+            public int Id { get; set; }
+            
+            [Projectable]
+            public int Computed(int argument) => Id + argument; 
+        }
+
+        [Scenario(NamingPolicy = ScenarioTestMethodNamingPolicy.Test)]
+        public void PlayScenario(ScenarioContext scenario)
+        {
+            // Setup
+            using var dbContext = new SampleDbContext<Entity>(); 
+
+            scenario.Fact("We can filter on a projectable property", () => {
+                const string expectedQueryString =
+@"DECLARE @__argument_0 int = 1;
+
+SELECT [e].[Id]
+FROM [Entity] AS [e]
+WHERE ([e].[Id] + @__argument_0) = 2";
+
+                var query = dbContext.Set<Entity>().AsQueryable()
+                    .Where(x => x.Computed(1) == 2);
+
+                Assert.Equal(expectedQueryString, query.ToQueryString());
+            });
+
+            scenario.Fact("We can select on a projectable property", () => {
+                const string expectedQueryString =
+@"DECLARE @__argument_0 int = 1;
+
+SELECT [e].[Id] + @__argument_0
+FROM [Entity] AS [e]";
+
+                var query = dbContext.Set<Entity>()
+                    .AsQueryable()
+                    .Select(x => x.Computed(1));
+
+                 Assert.Equal(expectedQueryString, query.ToQueryString());
+            });
+
+            scenario.Fact("We can pass in variables", () => {
+                const string expectedQueryString =
+@"DECLARE @__argument_0 int = 1;
+
+SELECT [e].[Id] + @__argument_0
+FROM [Entity] AS [e]";
+
+                var argument = 1;
+                var query = dbContext.Set<Entity>()
+                    .Select(x => x.Computed(argument));
+
+                Assert.Equal(expectedQueryString, query.ToQueryString());
+            });
+        }
+    }
+}

tests/EntityFrameworkCore.Projections.FunctionalTests/StatelessComplexFunctionTests.cs

@@ -5,6 +5,7 @@ using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using EntityFrameworkCore.Projections.FunctionalTests.Helpers;
+using EntityFrameworkCore.Projections.Services;
 using Microsoft.EntityFrameworkCore;
 using ScenarioTests;
 using Xunit;
@@ -28,25 +29,39 @@ namespace EntityFrameworkCore.Projections.FunctionalTests
             using var dbContext = new SampleDbContext<Entity>(); 
 
             scenario.Fact("We can filter on a projectable property", () => {
-                const string expectedQueryString = "SELECT [e].[Id]\r\nFROM [Entity] AS [e]\r\nWHERE 0 = 1";
+                const string expectedQueryString =
+@"DECLARE @__p_0 bit = CAST(0 AS bit);
 
-                var query = dbContext.Set<Entity>()
+SELECT [e].[Id]
+FROM [Entity] AS [e]
+WHERE @__p_0 = CAST(1 AS bit)";
+
+                var query = dbContext.Set<Entity>().AsQueryable()
                     .Where(x => x.Computed(0) == 1);
 
                 Assert.Equal(expectedQueryString, query.ToQueryString());
             });
 
             scenario.Fact("We can select on a projectable property", () => {
-                const string expectedQueryString = "SELECT 0\r\nFROM [Entity] AS [e]";
+                const string expectedQueryString =
+@"DECLARE @__argument1_0 int = 0;
+
+SELECT @__argument1_0
+FROM [Entity] AS [e]";
 
                 var query = dbContext.Set<Entity>()
+                    .AsQueryable()
                     .Select(x => x.Computed(0));
 
                  Assert.Equal(expectedQueryString, query.ToQueryString());
             });
 
             scenario.Fact("We can pass in variables", () => {
-                const string expectedQueryString = "SELECT 0\r\nFROM [Entity] AS [e]";
+                const string expectedQueryString =
+@"DECLARE @__argument1_0 int = 0;
+
+SELECT @__argument1_0
+FROM [Entity] AS [e]";
 
                 var argument = 0;
                 var query = dbContext.Set<Entity>()

tests/EntityFrameworkCore.Projections.Generator.Tests/ProjectionExpressionGeneratorTests.ArgumentlessProjectableComputedMethod.verified.txt

@@ -1,5 +1,6 @@
 using System;
 using EntityFrameworkCore.Projections;
+using Foo;
 
 namespace EntityFrameworkCore.Projections.Generated
 #nullable disable

tests/EntityFrameworkCore.Projections.Generator.Tests/ProjectionExpressionGeneratorTests.MoreComplexProjectableComputedProperty.verified.txt

@@ -1,5 +1,6 @@
 using System;
 using EntityFrameworkCore.Projections;
+using Foo;
 
 namespace EntityFrameworkCore.Projections.Generated
 #nullable disable

tests/EntityFrameworkCore.Projections.Generator.Tests/ProjectionExpressionGeneratorTests.ProjectableComputedMethodWithMultipleArguments.verified.txt

@@ -1,5 +1,6 @@
 using System;
 using EntityFrameworkCore.Projections;
+using Foo;
 
 namespace EntityFrameworkCore.Projections.Generated
 #nullable disable

tests/EntityFrameworkCore.Projections.Generator.Tests/ProjectionExpressionGeneratorTests.ProjectableComputedMethodWithSingleArgument.verified.txt

@@ -1,5 +1,6 @@
 using System;
 using EntityFrameworkCore.Projections;
+using Foo;
 
 namespace EntityFrameworkCore.Projections.Generated
 #nullable disable

tests/EntityFrameworkCore.Projections.Generator.Tests/ProjectionExpressionGeneratorTests.ProjectableComputedPropertyMethod.verified.txt

@@ -1,5 +1,6 @@
 using System;
 using EntityFrameworkCore.Projections;
+using Foo;
 
 namespace EntityFrameworkCore.Projections.Generated
 #nullable disable

tests/EntityFrameworkCore.Projections.Generator.Tests/ProjectionExpressionGeneratorTests.ProjectableComputedPropertyUsingThis.verified.txt

@@ -1,5 +1,6 @@
 using System;
 using EntityFrameworkCore.Projections;
+using Foo;
 
 namespace EntityFrameworkCore.Projections.Generated
 #nullable disable

tests/EntityFrameworkCore.Projections.Generator.Tests/ProjectionExpressionGeneratorTests.ProjectableExtensionMethod.verified.txt

@@ -0,0 +1,14 @@
+using System;
+using System.Linq;
+using EntityFrameworkCore.Projections;
+using Foo;
+
+namespace EntityFrameworkCore.Projections.Generated
+#nullable disable
+{
+    public static class Foo_C_Foo
+    {
+        public static System.Linq.Expressions.Expression<System.Func<Foo.D, int>> Expression(D d) => 
+            projectionTarget => 1;
+    }
+}

tests/EntityFrameworkCore.Projections.Generator.Tests/ProjectionExpressionGeneratorTests.ProjectablePropertyToNavigationalProperty.verified.txt

@@ -1,6 +1,7 @@
 using System;
 using System.Linq;
 using EntityFrameworkCore.Projections;
+using Foo;
 
 namespace EntityFrameworkCore.Projections.Generated
 #nullable disable

tests/EntityFrameworkCore.Projections.Generator.Tests/ProjectionExpressionGeneratorTests.SimpleProjectableComputedInNestedClassProperty.verified.txt

@@ -1,5 +1,6 @@
 using System;
 using EntityFrameworkCore.Projections;
+using Foo;
 
 namespace EntityFrameworkCore.Projections.Generated
 #nullable disable

tests/EntityFrameworkCore.Projections.Generator.Tests/ProjectionExpressionGeneratorTests.SimpleProjectableComputedProperty.verified.txt

@@ -1,5 +1,6 @@
 using System;
 using EntityFrameworkCore.Projections;
+using Foo;
 
 namespace EntityFrameworkCore.Projections.Generated
 #nullable disable

tests/EntityFrameworkCore.Projections.Generator.Tests/ProjectionExpressionGeneratorTests.SimpleProjectableMethod.verified.txt

@@ -1,5 +1,6 @@
 using System;
 using EntityFrameworkCore.Projections;
+using Foo;
 
 namespace EntityFrameworkCore.Projections.Generated
 #nullable disable

tests/EntityFrameworkCore.Projections.Generator.Tests/ProjectionExpressionGeneratorTests.SimpleProjectableProperty.verified.txt

@@ -1,5 +1,6 @@
 using System;
 using EntityFrameworkCore.Projections;
+using Foo;
 
 namespace EntityFrameworkCore.Projections.Generated
 #nullable disable

tests/EntityFrameworkCore.Projections.Generator.Tests/ProjectionExpressionGeneratorTests.cs

@@ -292,6 +292,31 @@ namespace Foo {
             return Verifier.Verify(result.GeneratedTrees[0].ToString());
         }
 
+        [Fact]
+        public Task ProjectableExtensionMethod()
+        {
+            var compilation = CreateCompilation(@"
+using System;
+using System.Linq;
+using EntityFrameworkCore.Projections;
+namespace Foo {
+    class D { }
+    
+    static class C {
+        [Projectable]
+        public static int Foo(this D d) => 1;
+    }
+}
+");
+
+            var result = RunGenerator(compilation);
+
+            Assert.Empty(result.Diagnostics);
+            Assert.Single(result.GeneratedTrees);
+
+            return Verifier.Verify(result.GeneratedTrees[0].ToString());
+        }
+
 
         #region Helpers