Fixed ToPageAsync extension when using a child projection expression (#8235)

Author: dannyheard7

src/GreenDonut/src/GreenDonut.Data.EntityFramework/Expressions/ExtractSelectExpressionVisitor.cs

@@ -12,7 +12,7 @@ protected override Expression VisitMethodCall(MethodCallExpression node)
     {
         if (node.Method.Name == _selectMethod && node.Arguments.Count == 2)
         {
-            var lambda = StripQuotes(node.Arguments[1]);
+            var lambda = ConvertToLambda(node.Arguments[1]);
             if (lambda.Type.IsGenericType
                 && lambda.Type.GetGenericTypeDefinition() == typeof(Func<,>))
             {
@@ -29,13 +29,20 @@ protected override Expression VisitMethodCall(MethodCallExpression node)
         return base.VisitMethodCall(node);
     }
 
-    private static LambdaExpression StripQuotes(Expression e)
+    private static LambdaExpression ConvertToLambda(Expression e)
     {
         while (e.NodeType == ExpressionType.Quote)
         {
             e = ((UnaryExpression)e).Operand;
         }
 
-        return (LambdaExpression)e;
+        if (e.NodeType != ExpressionType.MemberAccess)
+        {
+            return (LambdaExpression)e;
+        }
+
+        // Convert the property expression into a lambda expression
+        var typeArguments = e.Type.GetGenericArguments()[0].GetGenericArguments();
+        return Expression.Lambda(e,  Expression.Parameter(typeArguments[0]));
     }
 }

src/GreenDonut/test/GreenDonut.Data.EntityFramework.Tests/PagingHelperIntegrationTests.cs

@@ -1,3 +1,4 @@
+using System.Linq.Expressions;
 using GreenDonut.Data.TestContext;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.DependencyInjection;
@@ -178,6 +179,45 @@ await CreateSnapshot()
             .MatchMarkdownAsync();
     }
 
+    [Fact]
+    public async Task Paging_WithChildCollectionProjectionExpression_First_5()
+    {
+        // Arrange
+        var connectionString = CreateConnectionString();
+        await SeedAsync(connectionString);
+        using var capture = new CapturePagingQueryInterceptor();
+
+        // Act
+        await using var context = new CatalogContext(connectionString);
+
+        var pagingArgs = new PagingArguments
+        {
+            First = 5
+        };
+
+        var result = await context.Brands
+            .Select(BrandWithProductsDto.Projection)
+            .OrderBy(t => t.Name)
+            .ThenBy(t => t.Id)
+            .ToPageAsync(pagingArgs);
+
+        // Assert
+        await CreateSnapshot()
+            .AddQueries(capture.Queries)
+            .Add(
+                new
+                {
+                    result.HasNextPage,
+                    result.HasPreviousPage,
+                    First = result.First?.Id,
+                    FirstCursor = result.First is not null ? result.CreateCursor(result.First) : null,
+                    Last = result.Last?.Id,
+                    LastCursor = result.Last is not null ? result.CreateCursor(result.Last) : null
+                })
+            .Add(result.Items)
+            .MatchMarkdownAsync();
+    }
+
     [Fact]
     public async Task BatchPaging_First_5()
     {
@@ -351,6 +391,37 @@ public BrandDto(int id, string name)
         public string Name { get; }
     }
 
+    public class BrandWithProductsDto
+    {
+        public required int Id { get; init; }
+
+        public required string Name { get; init; }
+
+        public required IReadOnlyCollection<ProductDto> Products { get; init; }
+
+        public static Expression<Func<Brand, BrandWithProductsDto>> Projection
+            => brand => new BrandWithProductsDto
+            {
+                Id = brand.Id,
+                Name = brand.Name,
+                Products = brand.Products.AsQueryable().Select(ProductDto.Projection).ToList()
+            };
+    }
+
+    public class ProductDto
+    {
+        public required int Id { get; init; }
+
+        public required string Name { get; init; }
+
+        public static Expression<Func<Product, ProductDto>> Projection
+            => product => new ProductDto
+            {
+                Id = product.Id,
+                Name = product.Name
+            };
+    }
+
     public class ProductsByBrandDataLoader : StatefulBatchDataLoader<int, Page<Product>>
     {
         private readonly IServiceProvider _services;