Added discriminator for TPH tables

src/Directory.Build.props

@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <NoWarn>CS1591;NU5104;CS1573;CS9107;NU1608;NU1109</NoWarn>
-    <Version>34.2.0-beta.6</Version>
+    <Version>34.2.0-beta.7</Version>
     <LangVersion>preview</LangVersion>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <PackageTags>EntityFrameworkCore, EntityFramework, GraphQL</PackageTags>

src/GraphQL.EntityFramework/ForeignKeyExtractor.cs

@@ -30,6 +30,15 @@ static IReadOnlySet<string> GetForeignKeys(IEntityType entity)
             }
         }
 
+        // Include TPH discriminator property so projected entities maintain correct type identity.
+        // Without this, projected entities get the default discriminator value (e.g. enum value 0)
+        // instead of the actual value, causing downstream code that switches on the discriminator to fail.
+        var discriminator = entity.FindDiscriminatorProperty();
+        if (discriminator != null)
+        {
+            foreignKeyNames.Add(discriminator.Name);
+        }
+
         return foreignKeyNames;
     }
 }

src/Tests/IntegrationTests/Graphs/Discriminator/DiscriminatorBaseEntity.cs

@@ -0,0 +1,6 @@
+public abstract class DiscriminatorBaseEntity
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+    public DiscriminatorType EntityType { get; set; }
+    public string? Property { get; set; }
+}

src/Tests/IntegrationTests/Graphs/Discriminator/DiscriminatorDerivedAEntity.cs

@@ -0,0 +1,4 @@
+public class DiscriminatorDerivedAEntity : DiscriminatorBaseEntity
+{
+    public string? DerivedAProperty { get; set; }
+}

src/Tests/IntegrationTests/Graphs/Discriminator/DiscriminatorDerivedAGraphType.cs

@@ -0,0 +1,7 @@
+public class DiscriminatorDerivedAGraphType :
+    EfObjectGraphType<IntegrationDbContext, DiscriminatorDerivedAEntity>
+{
+    public DiscriminatorDerivedAGraphType(IEfGraphQLService<IntegrationDbContext> graphQlService) :
+        base(graphQlService) =>
+        AutoMap();
+}

src/Tests/IntegrationTests/Graphs/Discriminator/DiscriminatorDerivedBEntity.cs

@@ -0,0 +1,4 @@
+public class DiscriminatorDerivedBEntity : DiscriminatorBaseEntity
+{
+    public string? DerivedBProperty { get; set; }
+}

src/Tests/IntegrationTests/Graphs/Discriminator/DiscriminatorDerivedBGraphType.cs

@@ -0,0 +1,7 @@
+public class DiscriminatorDerivedBGraphType :
+    EfObjectGraphType<IntegrationDbContext, DiscriminatorDerivedBEntity>
+{
+    public DiscriminatorDerivedBGraphType(IEfGraphQLService<IntegrationDbContext> graphQlService) :
+        base(graphQlService) =>
+        AutoMap();
+}

src/Tests/IntegrationTests/Graphs/Discriminator/DiscriminatorType.cs

@@ -0,0 +1,5 @@
+public enum DiscriminatorType
+{
+    TypeA,
+    TypeB
+}

src/Tests/IntegrationTests/IntegrationDbContext.cs

@@ -44,6 +44,9 @@ protected override void OnConfiguring(DbContextOptionsBuilder builder) =>
     public DbSet<FilterBaseEntity> FilterBaseEntities { get; set; } = null!;
     public DbSet<FilterDerivedEntity> FilterDerivedEntities { get; set; } = null!;
     public DbSet<FilterReferenceEntity> FilterReferenceEntities { get; set; } = null!;
+    public DbSet<DiscriminatorBaseEntity> DiscriminatorBaseEntities { get; set; } = null!;
+    public DbSet<DiscriminatorDerivedAEntity> DiscriminatorDerivedAEntities { get; set; } = null!;
+    public DbSet<DiscriminatorDerivedBEntity> DiscriminatorDerivedBEntities { get; set; } = null!;
 
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {
@@ -126,5 +129,18 @@ protected override void OnModelCreating(ModelBuilder modelBuilder)
             .HasBaseType<FilterBaseEntity>();
         modelBuilder.Entity<FilterReferenceEntity>()
             .OrderBy(_ => _.Property);
+
+        // Configure TPH inheritance with CLR discriminator property for DiscriminatorBaseEntity hierarchy
+        modelBuilder.Entity<DiscriminatorBaseEntity>()
+            .HasDiscriminator(_ => _.EntityType)
+            .HasValue<DiscriminatorDerivedAEntity>(DiscriminatorType.TypeA)
+            .HasValue<DiscriminatorDerivedBEntity>(DiscriminatorType.TypeB)
+            .IsComplete();
+        modelBuilder.Entity<DiscriminatorDerivedAEntity>()
+            .HasBaseType<DiscriminatorBaseEntity>()
+            .OrderBy(_ => _.Property);
+        modelBuilder.Entity<DiscriminatorDerivedBEntity>()
+            .HasBaseType<DiscriminatorBaseEntity>()
+            .OrderBy(_ => _.Property);
     }
 }

src/Tests/IntegrationTests/IntegrationTests.CLR_discriminator_included_in_query_field_projection.verified.txt

@@ -0,0 +1,26 @@
+{
+  target:
+{
+  "data": {
+    "discriminatorDerivedAEntities": [
+      {
+        "entityType": "TYPE_A",
+        "property": "First"
+      },
+      {
+        "entityType": "TYPE_A",
+        "property": "Second"
+      }
+    ]
+  }
+},
+  sql: {
+    Text:
+select   d.Id,
+         d.EntityType,
+         d.Property
+from     DiscriminatorBaseEntities as d
+where    d.EntityType = 0
+order by d.Property
+  }
+}

src/Tests/IntegrationTests/IntegrationTests.CLR_discriminator_included_in_single_field_projection.verified.txt

@@ -0,0 +1,19 @@
+{
+  target:
+{
+  "data": {
+    "discriminatorDerivedAEntity": {
+      "property": "Value1"
+    }
+  }
+},
+  sql: {
+    Text:
+select top (2) d.Id,
+               d.EntityType,
+               d.Property
+from   DiscriminatorBaseEntities as d
+where  d.EntityType = 0
+       and d.Id = 'Guid_1'
+  }
+}

src/Tests/IntegrationTests/IntegrationTests.CLR_discriminator_returns_correct_value_when_queried.verified.txt

@@ -0,0 +1,20 @@
+{
+  target:
+{
+  "data": {
+    "discriminatorDerivedBEntity": {
+      "entityType": "TYPE_B",
+      "property": "ValueB"
+    }
+  }
+},
+  sql: {
+    Text:
+select top (2) d.Id,
+               d.EntityType,
+               d.Property
+from   DiscriminatorBaseEntities as d
+where  d.EntityType = 1
+       and d.Id = 'Guid_1'
+  }
+}

src/Tests/IntegrationTests/IntegrationTests.SchemaPrint.verified.txt

@@ -158,6 +158,10 @@
   filterReferenceEntities(id: ID, ids: [ID!], where: [WhereExpression!], orderBy: [OrderBy!], skip: Int, take: Int): [FilterReference!]!
   filterReferenceEntity(id: ID, ids: [ID!], where: [WhereExpression!]): FilterReference!
   filterReferenceEntityNullable(id: ID, ids: [ID!], where: [WhereExpression!]): FilterReference
+  discriminatorDerivedAEntities(id: ID, ids: [ID!], where: [WhereExpression!], orderBy: [OrderBy!], skip: Int, take: Int): [DiscriminatorDerivedA!]!
+  discriminatorDerivedAEntity(id: ID, ids: [ID!], where: [WhereExpression!]): DiscriminatorDerivedA!
+  discriminatorDerivedBEntities(id: ID, ids: [ID!], where: [WhereExpression!], orderBy: [OrderBy!], skip: Int, take: Int): [DiscriminatorDerivedB!]!
+  discriminatorDerivedBEntity(id: ID, ids: [ID!], where: [WhereExpression!]): DiscriminatorDerivedB!
 }
 
 type CustomType {
@@ -757,6 +761,25 @@ type FilterBase {
   id: ID!
 }
 
+type DiscriminatorDerivedA {
+  derivedAProperty: String
+  entityType: DiscriminatorType!
+  id: ID!
+  property: String
+}
+
+enum DiscriminatorType {
+  TYPE_A
+  TYPE_B
+}
+
+type DiscriminatorDerivedB {
+  derivedBProperty: String
+  entityType: DiscriminatorType!
+  id: ID!
+  property: String
+}
+
 type Mutation {
   parentEntityMutation(id: ID, ids: [ID!], where: [WhereExpression!]): Parent!
 }

src/Tests/IntegrationTests/IntegrationTests_clr_discriminator_projection.cs

@@ -0,0 +1,105 @@
+public partial class IntegrationTests
+{
+    /// <summary>
+    /// Verifies that when querying a concrete derived type in a TPH hierarchy with a CLR
+    /// discriminator property, the discriminator column is included in the SQL SELECT projection
+    /// even when it is not explicitly requested in the GraphQL query.
+    /// </summary>
+    [Fact]
+    public async Task CLR_discriminator_included_in_single_field_projection()
+    {
+        var entity = new DiscriminatorDerivedAEntity
+        {
+            Property = "Value1",
+            DerivedAProperty = "DerivedA1"
+        };
+
+        var query =
+            $$"""
+            {
+              discriminatorDerivedAEntity(id: "{{entity.Id}}")
+              {
+                property
+              }
+            }
+            """;
+
+        await using var database = await sqlInstance.Build();
+        await RunQuery(database, query, null, null, false, [entity]);
+    }
+
+    /// <summary>
+    /// Verifies that the CLR discriminator property returns the correct enum value
+    /// when explicitly requested in the GraphQL query, not the default enum value.
+    /// Without the fix, the projected entity would have EntityType = TypeA (default 0)
+    /// regardless of the actual discriminator value.
+    /// </summary>
+    [Fact]
+    public async Task CLR_discriminator_returns_correct_value_when_queried()
+    {
+        var entityA = new DiscriminatorDerivedAEntity
+        {
+            Property = "ValueA",
+            DerivedAProperty = "DerivedA"
+        };
+        var entityB = new DiscriminatorDerivedBEntity
+        {
+            Property = "ValueB",
+            DerivedBProperty = "DerivedB"
+        };
+
+        var query =
+            $$"""
+            {
+              discriminatorDerivedBEntity(id: "{{entityB.Id}}")
+              {
+                entityType
+                property
+              }
+            }
+            """;
+
+        await using var database = await sqlInstance.Build();
+        await RunQuery(database, query, null, null, false, [entityA, entityB]);
+    }
+
+    /// <summary>
+    /// Verifies that the CLR discriminator column is included in projection when querying
+    /// a list of derived entities, ensuring all returned entities have the correct
+    /// discriminator value.
+    /// </summary>
+    [Fact]
+    public async Task CLR_discriminator_included_in_query_field_projection()
+    {
+        var entity1 = new DiscriminatorDerivedAEntity
+        {
+            Property = "First",
+            DerivedAProperty = "DerivedA1"
+        };
+        var entity2 = new DiscriminatorDerivedAEntity
+        {
+            Property = "Second",
+            DerivedAProperty = "DerivedA2"
+        };
+        // This TypeB entity should not appear in TypeA query results
+        var entity3 = new DiscriminatorDerivedBEntity
+        {
+            Property = "Third",
+            DerivedBProperty = "DerivedB1"
+        };
+
+        var query =
+            """
+            {
+              discriminatorDerivedAEntities
+              {
+                entityType
+                property
+              }
+            }
+            """;
+
+        await using var database = await sqlInstance.Build();
+        await RunQuery(database, query, null, null, false, [entity1, entity2, entity3]);
+    }
+}

src/Tests/IntegrationTests/Query.cs

@@ -365,5 +365,21 @@ public Query(IEfGraphQLService<IntegrationDbContext> efGraphQlService)
             name: "filterReferenceEntityNullable",
             resolve: _ => _.DbContext.FilterReferenceEntities,
             nullable: true);
+
+        AddQueryField(
+            name: "discriminatorDerivedAEntities",
+            resolve: _ => _.DbContext.DiscriminatorDerivedAEntities);
+
+        AddSingleField(
+            name: "discriminatorDerivedAEntity",
+            resolve: _ => _.DbContext.DiscriminatorDerivedAEntities);
+
+        AddQueryField(
+            name: "discriminatorDerivedBEntities",
+            resolve: _ => _.DbContext.DiscriminatorDerivedBEntities);
+
+        AddSingleField(
+            name: "discriminatorDerivedBEntity",
+            resolve: _ => _.DbContext.DiscriminatorDerivedBEntities);
     }
 }

src/Tests/IntegrationTests/Schema.cs

@@ -44,6 +44,8 @@ public Schema(IServiceProvider resolver) :
         RegisterTypeMapping(typeof(FilterReferenceEntity), typeof(FilterReferenceGraphType));
         RegisterTypeMapping(typeof(FilterBaseEntity), typeof(FilterBaseGraphType));
         RegisterTypeMapping(typeof(FilterDerivedEntity), typeof(FilterDerivedGraphType));
+        RegisterTypeMapping(typeof(DiscriminatorDerivedAEntity), typeof(DiscriminatorDerivedAGraphType));
+        RegisterTypeMapping(typeof(DiscriminatorDerivedBEntity), typeof(DiscriminatorDerivedBGraphType));
         Query = (Query)resolver.GetService(typeof(Query))!;
         Mutation = (Mutation)resolver.GetService(typeof(Mutation))!;
         RegisterType(typeof(DerivedGraphType));