[release/10.0] Prevent DetectChanges failure for nulled nested complex collections

src/EFCore/ChangeTracking/Internal/InternalEntryBase.InternalComplexCollectionEntry.cs

@@ -26,6 +26,9 @@ private struct InternalComplexCollectionEntry(InternalEntryBase entry, IComplexP
         private static readonly bool UseOldBehavior37585 =
             AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore.Issue37585", out var enabled) && enabled;
 
+        private static readonly bool UseOldBehavior38632 =
+            AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore.Issue38632", out var enabled) && enabled;
+
         private List<InternalComplexEntry?>? _entries;
         private List<InternalComplexEntry?>? _originalEntries;
         private bool _isModified;
@@ -257,12 +260,6 @@ public InternalComplexEntry GetEntry(int ordinal, bool original = false)
                             ordinal, _complexCollection.DeclaringType.ShortNameChain(), _complexCollection.Name));
                 }
 
-                if (_containingEntry.GetOriginalValue(_complexCollection) == null)
-                {
-                    throw new InvalidOperationException(
-                        CoreStrings.ComplexCollectionEntryOriginalNull(
-                            _complexCollection.DeclaringType.ShortNameChain(), _complexCollection.Name));
-                }
             }
             else
             {
@@ -273,6 +270,29 @@ public InternalComplexEntry GetEntry(int ordinal, bool original = false)
                             ordinal, _complexCollection.DeclaringType.ShortNameChain(), _complexCollection.Name));
                 }
 
+            }
+
+            // Must check tracked entries first to allow reindexing during cleanup when the parent is null.
+            var existingEntries = original ? _originalEntries : _entries;
+            if (!UseOldBehavior38632
+                && existingEntries != null
+                && (uint)ordinal < (uint)existingEntries.Count
+                && existingEntries[ordinal] is { } existingEntry)
+            {
+                return existingEntry;
+            }
+
+            if (original)
+            {
+                if (_containingEntry.GetOriginalValue(_complexCollection) == null)
+                {
+                    throw new InvalidOperationException(
+                        CoreStrings.ComplexCollectionEntryOriginalNull(
+                            _complexCollection.DeclaringType.ShortNameChain(), _complexCollection.Name));
+                }
+            }
+            else
+            {
                 if (_containingEntry[_complexCollection] == null)
                 {
                     throw new InvalidOperationException(
@@ -292,10 +312,10 @@ public InternalComplexEntry GetEntry(int ordinal, bool original = false)
                             ordinal, _complexCollection.DeclaringType.ShortNameChain(), _complexCollection.Name, entries.Count));
             }
 
-            var complexEntry = entries[ordinal];
-            if (complexEntry != null)
+            if (UseOldBehavior38632
+                && entries[ordinal] is { } existingEntryAfterValidation)
             {
-                return complexEntry;
+                return existingEntryAfterValidation;
             }
 
             // The currentEntry is created in Detached state, so it's not added to the entries list yet.

test/EFCore.Relational.Specification.Tests/Update/ComplexCollectionJsonUpdateTestBase.cs

@@ -641,6 +641,30 @@ public virtual Task Grow_nested_sub_collection_in_complex_property_mapped_to_jso
                 }
             });
 
+    [ConditionalFact]
+    public virtual Task Set_nullable_complex_property_with_nested_collection_to_null()
+        => TestHelpers.ExecuteWithStrategyInTransactionAsync(
+            CreateContext,
+            UseTransaction,
+            async context =>
+            {
+                var entity = await context.Set<EntityWithNullableMeta>().OrderBy(e => e.Id).FirstAsync();
+
+                entity.Items[0].Meta = null;
+
+                ClearLog();
+                await context.SaveChangesAsync();
+            },
+            async context =>
+            {
+                using (SuspendRecordingEvents())
+                {
+                    var entity = await context.Set<EntityWithNullableMeta>().OrderBy(e => e.Id).FirstAsync();
+                    Assert.Single(entity.Items);
+                    Assert.Null(entity.Items[0].Meta);
+                }
+            });
+
     protected virtual void UseTransaction(DatabaseFacade facade, IDbContextTransaction transaction)
         => facade.UseTransaction(transaction.GetDbTransaction());
 
@@ -657,6 +681,7 @@ protected class ComplexCollectionJsonContext(DbContextOptions options) : DbConte
     {
         public DbSet<CompanyWithComplexCollections> Companies { get; set; } = null!;
         public DbSet<WidgetWithDeepJson> Widgets { get; set; } = null!;
+        public DbSet<EntityWithNullableMeta> EntitiesWithNullableMeta { get; set; } = null!;
     }
 
     protected class CompanyWithComplexCollections
@@ -723,6 +748,28 @@ protected class InnerEntry
         public required string Value { get; set; }
     }
 
+    protected class EntityWithNullableMeta
+    {
+        public int Id { get; set; }
+        public List<ItemWithMeta> Items { get; set; } = [];
+    }
+
+    protected class ItemWithMeta
+    {
+        public required string Name { get; set; }
+        public OptionalMeta? Meta { get; set; }
+    }
+
+    protected class OptionalMeta
+    {
+        public List<MetaEntry> Entries { get; set; } = [];
+    }
+
+    protected class MetaEntry
+    {
+        public required string Value { get; set; }
+    }
+
     public abstract class ComplexCollectionJsonUpdateFixtureBase : SharedStoreFixtureBase<DbContext>
     {
         protected override string StoreName
@@ -783,6 +830,20 @@ protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext con
                                     }));
                     });
             });
+
+            modelBuilder.Entity<EntityWithNullableMeta>(b =>
+            {
+                b.Property(x => x.Id).ValueGeneratedNever();
+
+                b.ComplexCollection(
+                    x => x.Items, ib =>
+                    {
+                        ib.ToJson();
+                        ib.ComplexProperty(
+                            x => x.Meta, mb =>
+                                mb.ComplexCollection(m => m.Entries));
+                    });
+            });
         }
 
         protected override Task SeedAsync(DbContext context)
@@ -837,6 +898,28 @@ protected override Task SeedAsync(DbContext context)
             };
 
             context.Add(widget);
+
+            var entityWithNullableMeta = new EntityWithNullableMeta
+            {
+                Id = 1,
+                Items =
+                [
+                    new ItemWithMeta
+                    {
+                        Name = "Item1",
+                        Meta = new OptionalMeta
+                        {
+                            Entries =
+                            [
+                                new MetaEntry { Value = "entry-0" },
+                                new MetaEntry { Value = "entry-1" }
+                            ]
+                        }
+                    }
+                ]
+            };
+
+            context.Add(entityWithNullableMeta);
             return context.SaveChangesAsync();
         }
     }

test/EFCore.SqlServer.FunctionalTests/Update/ComplexCollectionJsonUpdateSqlServerTest.cs

@@ -345,6 +345,23 @@ OUTPUT 1
 """);
     }
 
+    public override async Task Set_nullable_complex_property_with_nested_collection_to_null()
+    {
+        await base.Set_nullable_complex_property_with_nested_collection_to_null();
+
+        AssertSql(
+            """
+@p0='[{"Name":"Item1","Meta":null}]' (Nullable = false) (Size = 30)
+@p1='1'
+
+SET IMPLICIT_TRANSACTIONS OFF;
+SET NOCOUNT ON;
+UPDATE [EntitiesWithNullableMeta] SET [Items] = @p0
+OUTPUT 1
+WHERE [Id] = @p1;
+""");
+    }
+
     public class ComplexCollectionJsonUpdateSqlServerFixture : ComplexCollectionJsonUpdateFixtureBase
     {
         protected override ITestStoreFactory TestStoreFactory

test/EFCore.Sqlite.FunctionalTests/Update/ComplexCollectionJsonUpdateSqliteTest.cs

@@ -305,6 +305,21 @@ public override async Task Grow_nested_sub_collection_in_complex_property_mapped
 """);
     }
 
+    public override async Task Set_nullable_complex_property_with_nested_collection_to_null()
+    {
+        await base.Set_nullable_complex_property_with_nested_collection_to_null();
+
+        AssertSql(
+            """
+@p0='[{"Name":"Item1","Meta":null}]' (Nullable = false) (Size = 30)
+@p1='1'
+
+UPDATE "EntitiesWithNullableMeta" SET "Items" = @p0
+WHERE "Id" = @p1
+RETURNING 1;
+""");
+    }
+
     public class ComplexCollectionJsonUpdateSqliteFixture : ComplexCollectionJsonUpdateFixtureBase
     {
         protected override ITestStoreFactory TestStoreFactory