Changes of nullable complex property with discriminator are not recognized

[peterwurzinger]

Bug description

Given an entity that contains a nullable complex property with a discriminator, changes of this nullable complex property away from null are not persisted - or at least not entirely.

To be precise, on a database level it seems, that the child-properties of that nullable complex properties are indeed saved, but the discriminator property stays unchanged. Subsequent reads of that instance therefore see the discriminator property with its empty-value, therefore assuming that the whole property isn't set at all and materializing it to null.

Your code

#:package Microsoft.EntityFrameworkCore.SqlServer@10.0.6
#:property PublishAot=false

using Microsoft.EntityFrameworkCore;

await using var context = new EntityContext();
await context.Database.EnsureDeletedAsync();
await context.Database.EnsureCreatedAsync();

var entity = new Entity();
context.Entities.Add(entity);

await context.SaveChangesAsync();
context.ChangeTracker.Clear();

entity = await context.Entities.SingleAsync();
entity.Prop = new OptionalComplexProperty()
{
  //The database column shows the "null" value
  OptionalValue = true
};

await context.SaveChangesAsync();
context.ChangeTracker.Clear();

entity = await context.Entities.SingleAsync();

//Should print "True", actually prints "null"
Console.WriteLine(entity.Prop?.ToString() ?? "null");

public class EntityContext : DbContext
{
  protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    => optionsBuilder.UseSqlServer("Server=(localdb)\\MSSQLLocalDB;Initial Catalog=DiscriminatorRepro;Integrated Security=true");

  public DbSet<Entity> Entities { get; set;} = null!;
  protected override void OnModelCreating(ModelBuilder modelBuilder)
  {
    var entity = modelBuilder.Entity<Entity>();
    entity.HasKey(p => p.Id);

    var compl = entity.ComplexProperty(p => p.Prop);
    compl.HasDiscriminator();
  }
}

public class Entity
{
  public Guid Id { get; set; } = Guid.NewGuid();
  public OptionalComplexProperty? Prop { get; set; }
}

public class OptionalComplexProperty
{
  public bool? OptionalValue { get; set; }
}

Stack traces

Verbose output

EF Core version

10.0.6

Database provider

Microsoft.EntityFrameworkCore.SqlServer

Target framework

.NET 10

Operating system

Windows 11

IDE

No response

[roji]

Seems like a duplicate of #37386 (but see also #38105), leaving to @AndriySvyryd to confirm/take a look.

[peterwurzinger]

#37386 was created by me as well, that seems fixed since 10.0.4 - at I could verify that for types without discriminator. But it looks like a variant, yes.

[roji]

@peterwurzinger are you saying you can confirm #37386 is fixed since 10.0.4, but the case described here still fails?

[peterwurzinger]

@roji Yes. I just had a look, we had 5 annotations in various DbContext configurations waiting for #37386 to be fixed - 4 are confirmed working since the 10.0.4 release in February.

One that followed the configuration described in this issue here was reported as regression.

[roji]

AI Triage

The below is an AI-generated analysis and may contain inaccuracies.

Issue type: Bug
Area labels added: area-change-tracking, area-complex-types

Confirmed Bug

Reproduced on SQLite with EF Core 10.0.6. The bug is present on all 10.0.x versions (10.0.0 through 10.0. it has existed since the nullable complex property + discriminator feature was first shipped. This is not a regression from the #37386 fix; the discriminator-specific code path was never correct.6)

The issue is distinct from #37386 (which was about non-discriminator optional complex properties and is confirmed fixed since 10.0.4).

Root Cause

In ChangeDetector.DetectComplexPropertyChange(), when a nullable complex property transitions from null to non-null, all inner properties are marked as but only if GetAfterSaveBehavior() == PropertySaveBehavior.Save:modified

foreach (var innerProperty in complexProperty.ComplexType.GetFlattenedProperties())
{
    if (innerProperty.GetOriginalValueIndex() >= 0
        && innerProperty.GetAfterSaveBehavior() == PropertySaveBehavior. excludes discriminatorsSave  // 
        && entry.IsLoaded(innerProperty))
    {
        entry.SetPropertyModified(innerProperty);
    }
}

Discriminator properties are configured with PropertySaveBehavior.Throw, so they are skipped. As a result, the UPDATE statement includes child property values but not the discriminator column. On subsequent reads, the NULL discriminator causes EF to materialize the complex property as null.

SQL Evidence

The generated UPDATE only sets Prop_OptionalValue but omits Prop_Discriminator:

UPDATE "Entities" SET "Prop_OptionalValue" = @p0
WHERE "Id" = @p1
RETURNING 1;

Possible Duplicates

• Related but confirmed fixed (non-discriminator variant); this issue is the discriminator-specific residual bug37386

• Related discriminator regression (init-only discriminator marked as modified when unchanged), now closed38105

Minimal repro

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;

await using var context = new TestContext();
await context.Database.EnsureDeletedAsync();
await context.Database.EnsureCreatedAsync();

var entity = new Entity();
context.Entities.Add(entity);
await context.SaveChangesAsync();
context.ChangeTracker.Clear();

entity = await context.Entities.SingleAsync();
entity.Prop = new OptionalComplexProperty { OptionalValue = true };
await context.SaveChangesAsync();
context.ChangeTracker.Clear();

entity = await context.Entities.SingleAsync();
// Should print "True", actually prints "null"
Console.WriteLine(entity.Prop?.OptionalValue?.ToString() ?? "null");

public class TestContext : DbContext
{
    public DbSet<Entity> Entities { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseSqlite("Data Source=repro38119.db")
            .LogTo(Console.WriteLine, LogLevel.Information)
            .EnableSensitiveDataLogging();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Entity>().ComplexProperty(p => p.Prop).HasDiscriminator();
    }
}

public class Entity
{
    public Guid Id { get; set; } = Guid.NewGuid();
    public OptionalComplexProperty? Prop { get; set; }
}

public class OptionalComplexProperty
{
    public bool? OptionalValue { get; set; }
}

Requires a Microsoft.EntityFrameworkCore.Sqlite package reference (version 10.0.0+). The program prints null instead of the expected True.