Fix shadow discriminators on complex types by skipping shadow properties on complex types in snapshot creation (#37394)

Fixes #37337

Author: Copilot

src/EFCore/ChangeTracking/Internal/SnapshotFactoryFactory.cs

@@ -14,6 +14,9 @@ namespace Microsoft.EntityFrameworkCore.ChangeTracking.Internal;
 /// </summary>
 public abstract class SnapshotFactoryFactory
 {
+    private static readonly bool UseOldBehavior37337 =
+        AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore.Issue37337", out var enabled) && enabled;
+
     /// <summary>
     ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
     ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
@@ -139,6 +142,14 @@ protected virtual Expression CreateSnapshotExpression(
                     continue;
 
                 case IProperty property:
+                    // Shadow property materialization on complex types is not currently supported (see #35613).
+                    if (!UseOldBehavior37337 && propertyBase.DeclaringType is IComplexType && property.IsShadowProperty())
+                    {
+                        arguments[i] = propertyBase.ClrType.GetDefaultValueConstant();
+                        types[i] = propertyBase.ClrType;
+                        continue;
+                    }
+
                     arguments[i] = CreateSnapshotValueExpression(CreateReadValueExpression(parameter, property), property);
                     continue;
 

test/EFCore.Specification.Tests/Query/AdHocComplexTypeQueryTestBase.cs

@@ -268,6 +268,65 @@ public class ComplexTypeWithAllNulls
 
     #endregion 37162
 
+    #region Issue37337
+
+    [ConditionalFact]
+    public virtual async Task Nullable_complex_type_with_discriminator_and_shadow_property()
+    {
+        var contextFactory = await InitializeAsync<Context37337>(
+            seed: context =>
+            {
+                context.Add(
+                    new Context37337.EntityType
+                    {
+                        Prop = new Context37337.OptionalComplexProperty
+                        {
+                            OptionalValue = true
+                        }
+                    });
+                return context.SaveChangesAsync();
+            });
+
+        await using var context = contextFactory.CreateContext();
+
+        var entities = await context.Set<Context37337.EntityType>().ToArrayAsync();
+
+        Assert.Single(entities);
+        var entity = entities[0];
+        Assert.NotNull(entity.Prop);
+        Assert.True(entity.Prop.OptionalValue);
+    }
+
+    private class Context37337(DbContextOptions options) : DbContext(options)
+    {
+        protected override void OnModelCreating(ModelBuilder modelBuilder)
+        {
+            var entity = modelBuilder.Entity<EntityType>();
+            entity.Property(p => p.Id);
+            entity.HasKey(p => p.Id);
+
+            var compl = entity.ComplexProperty(p => p.Prop);
+            compl.Property(p => p.OptionalValue);
+            compl.HasDiscriminator();
+
+            // Shadow property added via convention (e.g., audit field)
+            entity.Property<string>("CreatedBy").IsRequired(false);
+        }
+
+        public class EntityType
+        {
+            public Guid Id { get; set; }
+            public OptionalComplexProperty? Prop { get; set; }
+        }
+
+        public class OptionalComplexProperty
+        {
+            public bool? OptionalValue { get; set; }
+        }
+    }
+
+    #endregion Issue37337
+
     protected override string StoreName
         => "AdHocComplexTypeQueryTest";
 }