Add support for projections in batch resolvers

src/HotChocolate/Core/src/Types.Analyzers/FileBuilders/TypeFileBuilderBase.cs

@@ -1119,6 +1119,39 @@ private void WriteBatchResolver(
                             parameter.Key);
                         break;
 
+                    case ResolverParameterKind.Selection:
+                        Writer.WriteIndentedLine(
+                            "var args{0} = contexts[0].Selection;",
+                            i);
+                        break;
+
+                    case ResolverParameterKind.QueryContext:
+                        var entityType = parameter.TypeParameters[0].ToFullyQualified();
+                        Writer.WriteIndentedLine("var args{0}_selection = contexts[0].Selection;", i);
+                        Writer.WriteIndentedLine("var args{0}_filter = global::{1}.GetFilterContext(contexts[0]);",
+                            i,
+                            WellKnownTypes.FilterContextResolverContextExtensions);
+                        Writer.WriteIndentedLine("var args{0}_sorting = global::{1}.GetSortingContext(contexts[0]);",
+                            i,
+                            WellKnownTypes.SortingContextResolverContextExtensions);
+                        Writer.WriteIndentedLine(
+                            "var args{0} = new global::{1}<{2}>(",
+                            i,
+                            WellKnownTypes.QueryContext,
+                            entityType);
+                        using (Writer.IncreaseIndent())
+                        {
+                            Writer.WriteIndentedLine(
+                                "global::{0}.AsSelector<{1}>(args{2}_selection, contexts[0].IncludeFlags),",
+                                WellKnownTypes.HotChocolateExecutionSelectionExtensions,
+                                entityType,
+                                i);
+                            Writer.WriteIndentedLine("args{0}_filter?.AsPredicate<{1}>(),", i, entityType);
+                            Writer.WriteIndentedLine("args{0}_sorting?.AsSortDefinition<{1}>());", i, entityType);
+                        }
+
+                        break;
+
                     default:
                         // Fallback for any other kind: extract from first context
                         Writer.WriteIndentedLine(
@@ -1653,6 +1686,12 @@ private void WriteResolverArguments(Resolver resolver, IMethodSymbol resolverMet
                         WellKnownTypes.ConnectionFlagsHelper);
                     break;
 
+                case ResolverParameterKind.Selection:
+                    Writer.WriteIndentedLine(
+                        "var args{0} = context.Selection;",
+                        i);
+                    break;
+
                 case ResolverParameterKind.Unknown:
                     Writer.WriteIndentedLine(
                         "var args{0} = _binding_{1}_{2}.Execute<{3}>(context);",

src/HotChocolate/Core/src/Types.Analyzers/Helpers/CompilationExtensions.cs

@@ -417,6 +417,11 @@ public static ResolverParameterKind GetParameterKind(
             return ResolverParameterKind.ConnectionFlags;
         }
 
+        if (parameter.IsSelection())
+        {
+            return ResolverParameterKind.Selection;
+        }
+
         return ResolverParameterKind.Unknown;
     }
 }

src/HotChocolate/Core/src/Types.Analyzers/Helpers/SymbolExtensions.cs

@@ -777,6 +777,9 @@ public static bool IsPagingArguments(this IParameterSymbol parameter)
         => parameter.Type is INamedTypeSymbol namedTypeSymbol
             && namedTypeSymbol.ToDisplayString().StartsWith(WellKnownTypes.PagingArguments);
 
+    public static bool IsSelection(this IParameterSymbol parameter)
+        => parameter.Type.ToDisplayString() == WellKnownTypes.ISelection;
+
     public static bool IsGlobalState(
         this IParameterSymbol parameter,
         [NotNullWhen(true)] out string? key)

src/HotChocolate/Core/src/Types.Analyzers/Models/ResolverParameter.cs

@@ -88,7 +88,8 @@ ResolverParameterKind.EventMessage or
             ResolverParameterKind.FieldNode or
             ResolverParameterKind.OutputField or
             ResolverParameterKind.ClaimsPrincipal or
-            ResolverParameterKind.ConnectionFlags;
+            ResolverParameterKind.ConnectionFlags or
+            ResolverParameterKind.Selection;
 
     public bool RequiresBinding
         => Kind == ResolverParameterKind.Unknown;

src/HotChocolate/Core/src/Types.Analyzers/Models/ResolverParameterKind.cs

@@ -23,5 +23,6 @@ public enum ResolverParameterKind
     Argument,
     QueryContext,
     PagingArguments,
-    ConnectionFlags
+    ConnectionFlags,
+    Selection
 }

src/HotChocolate/Core/src/Types.Analyzers/WellKnownTypes.cs

@@ -110,6 +110,7 @@ public static class WellKnownTypes
     public const string ImmutableArrayOfMiddlewareContext = "System.Collections.Immutable.ImmutableArray<HotChocolate.Resolvers.IMiddlewareContext>";
     public const string IList = "System.Collections.IList";
     public const string MiddlewareContext = "HotChocolate.Resolvers.IMiddlewareContext";
+    public const string ISelection = "HotChocolate.Execution.ISelection";
 
     public static HashSet<string> TypeClass { get; } =
     [

src/HotChocolate/Data/test/Data.PostgreSQL.Tests/Data/CatalogContext.cs

@@ -12,12 +12,15 @@ public class CatalogContext(DbContextOptions<CatalogContext> options) : DbContex
 
     public DbSet<Brand> Brands => Set<Brand>();
 
+    public DbSet<Supplier> Suppliers => Set<Supplier>();
+
     public DbSet<SingleProperty> SingleProperties => Set<SingleProperty>();
 
     protected override void OnModelCreating(ModelBuilder builder)
     {
         builder.ApplyConfiguration(new BrandEntityTypeConfiguration());
         builder.ApplyConfiguration(new ProductTypeEntityTypeConfiguration());
         builder.ApplyConfiguration(new ProductEntityTypeConfiguration());
+        builder.ApplyConfiguration(new SupplierEntityTypeConfiguration());
     }
 }

src/HotChocolate/Data/test/Data.PostgreSQL.Tests/Data/EntityConfigurations/BrandEntityTypeConfiguration.cs

@@ -14,5 +14,10 @@ public void Configure(EntityTypeBuilder<Brand> builder)
         builder
             .Property(cb => cb.Name)
             .HasMaxLength(100);
+
+        builder
+            .HasOne(cb => cb.Supplier)
+            .WithMany(s => s.Brands)
+            .HasForeignKey(cb => cb.SupplierId);
     }
 }

src/HotChocolate/Data/test/Data.PostgreSQL.Tests/Data/EntityConfigurations/SupplierEntityTypeConfiguration.cs

@@ -0,0 +1,26 @@
+using HotChocolate.Data.Models;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace HotChocolate.Data.Data.EntityConfigurations;
+
+internal sealed class SupplierEntityTypeConfiguration : IEntityTypeConfiguration<Supplier>
+{
+    public void Configure(EntityTypeBuilder<Supplier> builder)
+    {
+        builder
+            .ToTable("Suppliers");
+
+        builder
+            .Property(s => s.Name)
+            .HasMaxLength(100);
+
+        builder
+            .Property(s => s.Website)
+            .HasMaxLength(256);
+
+        builder
+            .Property(s => s.ContactEmail)
+            .HasMaxLength(256);
+    }
+}

src/HotChocolate/Data/test/Data.PostgreSQL.Tests/IntegrationTests.cs

@@ -125,6 +125,33 @@ public async Task Query_Brands_With_BatchResolver_ProductCount()
         MatchSnapshot(result, interceptor);
     }
 
+    [Fact]
+    public async Task Query_Brands_With_BatchResolver_Supplier()
+    {
+        // arrange
+        using var interceptor = new TestQueryInterceptor();
+
+        // act
+        var result = await ExecuteAsync(
+            """
+            {
+                brands(first: 5) {
+                    nodes {
+                        id
+                        name
+                        supplier {
+                            name
+                            website
+                        }
+                    }
+                }
+            }
+            """);
+
+        // assert
+        MatchSnapshot(result, interceptor);
+    }
+
     [Fact]
     public async Task Query_Brands_First_2_And_Products_First_2_Name_Desc()
     {

src/HotChocolate/Data/test/Data.PostgreSQL.Tests/Migrations/CatalogContextSeed.cs

@@ -16,9 +16,27 @@ public async Task SeedAsync(CatalogContext context)
             var sourceJson = FileResource.Open("catalog.json");
             var sourceItems = JsonSerializer.Deserialize<ProductEntry[]>(sourceJson)!;
 
+            // Seed suppliers first (brands will reference them).
+            context.Suppliers.RemoveRange(context.Suppliers);
+            var suppliers = new[]
+            {
+                new Supplier { Name = "Global Supply Co.", Website = "https://globalsupply.example.com", ContactEmail = "info@globalsupply.example.com" },
+                new Supplier { Name = "Prime Distribution", Website = "https://primedist.example.com", ContactEmail = "sales@primedist.example.com" },
+                new Supplier { Name = "Atlas Logistics", Website = "https://atlaslogistics.example.com", ContactEmail = "contact@atlaslogistics.example.com" }
+            };
+            await context.Suppliers.AddRangeAsync(suppliers);
+            await context.SaveChangesAsync();
+
+            var supplierIds = await context.Suppliers.Select(s => s.Id).ToListAsync();
+
             context.Brands.RemoveRange(context.Brands);
+            var brandNames = sourceItems.Select(x => x.Brand).Distinct().ToList();
             await context.Brands.AddRangeAsync(
-                sourceItems.Select(x => x.Brand).Distinct().Select(brandName => new Brand { Name = brandName }));
+                brandNames.Select((brandName, i) => new Brand
+                {
+                    Name = brandName,
+                    SupplierId = supplierIds[i % supplierIds.Count]
+                }));
 
             context.ProductTypes.RemoveRange(context.ProductTypes);
             await context.ProductTypes.AddRangeAsync(

src/HotChocolate/Data/test/Data.PostgreSQL.Tests/Models/Brand.cs

@@ -11,5 +11,9 @@ public sealed class Brand
     [Required]
     public string Name { get; set; } = null!;
 
+    public int SupplierId { get; set; }
+
+    public Supplier? Supplier { get; set; }
+
     public ICollection<Product> Products { get; set; } = [];
 }

src/HotChocolate/Data/test/Data.PostgreSQL.Tests/Models/Supplier.cs

@@ -0,0 +1,17 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace HotChocolate.Data.Models;
+
+public sealed class Supplier
+{
+    public int Id { get; set; }
+
+    [Required]
+    public string Name { get; set; } = null!;
+
+    public string? Website { get; set; }
+
+    public string? ContactEmail { get; set; }
+
+    public ICollection<Brand> Brands { get; set; } = [];
+}

src/HotChocolate/Data/test/Data.PostgreSQL.Tests/Types/Brands/BrandNode.cs

@@ -50,4 +50,25 @@ public static async Task<List<int>> GetProductCountAsync(
 
         return brands.Select(b => counts.GetValueOrDefault(b.Id, 0)).ToList();
     }
+
+    [BindMember(nameof(Brand.SupplierId))]
+    [BatchResolver]
+    public static async Task<List<Supplier?>> GetSupplierAsync(
+        [Parent(requires: nameof(Brand.SupplierId))] List<Brand> brands,
+        QueryContext<Supplier> query,
+        [Service] CatalogContext context,
+        CancellationToken cancellationToken)
+    {
+        var supplierIds = brands.Select(b => b.SupplierId).Distinct().ToList();
+
+        var queryable = context.Suppliers
+            .Where(s => supplierIds.Contains(s.Id))
+            .With(query.Include(s => s.Id));
+        PagingQueryInterceptor.Publish(queryable);
+
+        var suppliers = await queryable
+            .ToDictionaryAsync(s => s.Id, cancellationToken);
+
+        return brands.Select(b => suppliers.GetValueOrDefault(b.SupplierId)).ToList();
+    }
 }

src/HotChocolate/Data/test/Data.PostgreSQL.Tests/__snapshots__/IntegrationTests.CreateSchema.graphql

@@ -19,6 +19,7 @@ type BillingStatementTransaction implements StatementTransaction {
 type Brand implements Node {
   products("Returns the first _n_ elements from the list." first: Int "Returns the elements in the list that come after the specified cursor." after: String "Returns the last _n_ elements from the list." last: Int "Returns the elements in the list that come before the specified cursor." before: String where: ProductFilterInput @cost(weight: "10") order: [ProductSortInput!] @cost(weight: "10")): BrandProductsConnection! @listSize(assumedSize: 50, slicingArguments: ["first", "last"], slicingArgumentDefaultValue: 10, sizedFields: ["edges", "nodes"], requireOneSlicingArgument: false) @cost(weight: "10")
   productCount: Int! @cost(weight: "10")
+  supplier: Supplier @cost(weight: "10")
   id: ID!
   name: String!
 }
@@ -182,6 +183,14 @@ type SingleProperty {
   id: String!
 }
 
+type Supplier {
+  id: Int!
+  name: String!
+  website: String
+  contactEmail: String
+  brands: [Brand!]!
+}
+
 input BooleanOperationFilterInput {
   eq: Boolean @cost(weight: "10")
   neq: Boolean @cost(weight: "10")
@@ -192,6 +201,7 @@ input BrandFilterInput {
   or: [BrandFilterInput!]
   id: IntOperationFilterInput
   name: StringOperationFilterInput
+  supplier: SupplierFilterInput
   products: ListFilterInputTypeOfProductFilterInput
 }
 
@@ -235,6 +245,13 @@ input IntOperationFilterInput {
   nlte: Int @cost(weight: "10")
 }
 
+input ListFilterInputTypeOfBrandFilterInput {
+  all: BrandFilterInput @cost(weight: "10")
+  none: BrandFilterInput @cost(weight: "10")
+  some: BrandFilterInput @cost(weight: "10")
+  any: Boolean @cost(weight: "10")
+}
+
 input ListFilterInputTypeOfProductFilterInput {
   all: ProductFilterInput @cost(weight: "10")
   none: ProductFilterInput @cost(weight: "10")
@@ -289,6 +306,16 @@ input StringOperationFilterInput {
   nendsWith: String @cost(weight: "20")
 }
 
+input SupplierFilterInput {
+  and: [SupplierFilterInput!]
+  or: [SupplierFilterInput!]
+  id: IntOperationFilterInput
+  name: StringOperationFilterInput
+  website: StringOperationFilterInput
+  contactEmail: StringOperationFilterInput
+  brands: ListFilterInputTypeOfBrandFilterInput
+}
+
 "Defines the possible serialization types for GraphQL scalar values."
 enum ScalarSerializationType {
   "The scalar serializes to a string value."
@@ -329,7 +356,7 @@ type User @internal {
   id: ID!
   name: String!
 }
-
+            
 directive @internal on OBJECT | FIELD_DEFINITION
 """
 directive @internal on OBJECT | FIELD_DEFINITION
@@ -350,11 +377,11 @@ directive @serializeAs("The primitive type a scalar is serialized to." type: [Sc
 By default, only a single source schema is allowed to contribute
 a particular field to an object type.
 
-
+            
 This prevents source schemas from inadvertently defining similarly named
 fields that are not semantically equivalent.
 
-
+            
 Fields must be explicitly marked as @shareable to allow multiple source
 schemas to define them, ensuring that the decision to serve a field from
 more than one source schema is intentional and coordinated.