Use of InMemoryDatabaseRoot breaks OwnsOne in InMemoryDatabase

[alalloo]

Owning entity has two members of same type, both marked with OwnsOne. Without use of InMemoryDatabaseRoot entities can be saved, but with use - and no other changes two unexpected behaviors occur

• unset (null) property A gets the value of B
• if both are in fact set to different object, ef throws claiming duplicate key

Steps to reproduce

public class OwningEntity
{
    public int Id { get; set; }
    public string Name { get; set; }
    public OwnedEntity OwnedA { get; set; }
    public OwnedEntity OwnedB { get; set; }
}

public class OwnedEntity
{
    public int A { get; set; }
    public string B { get; set; }
}

public class MyDbContext : DbContext
{
    public DbSet<OwningEntity> OwningEntities { get; set; }
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Entity<OwningEntity>().OwnsOne(o => o.OwnedA);
        modelBuilder.Entity<OwningEntity>().OwnsOne(o => o.OwnedB);
    }
}

Test code includes an InMemoryDbContext with a parameter controlling whether a db root should be used or not:

public class InMemoryMyDbContext : MyDbContext
{
    private string dbName;
    private bool useRoot;

	public InMemoryMyDbContext(string dbName, bool useRoot)
	{
		this.dbName = dbName;
		this.useRoot = useRoot;
	}

	protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
	{
		if (useRoot)
		{
			optionsBuilder.UseInMemoryDatabase(dbName, InMemoryDbRoot.DbRoot);
		}
		else
		{
			optionsBuilder.UseInMemoryDatabase(dbName);
		}
		base.OnConfiguring(optionsBuilder);
	}
}

public class InMemoryDbRoot
{
	private static readonly object DbRootInitLock = new object();
	private static InMemoryDatabaseRoot root;
	public static InMemoryDatabaseRoot DbRoot
	{
		get
		{
			{
				lock (DbRootInitLock)
				{
					if (root == null)
					{
						root = new InMemoryDatabaseRoot();
					}
					return root;
				}
			}
		}
	}
}

Finally, two tests which fail or pass only depending on the useRoot boolean:

[TestClass]
public class UnitTest1
{
	// Not rooted - tests pass
	// const bool useRoot = false;
	// Rooted - tests fail
	const bool useRoot = true;

	[TestMethod]
	public async Task TestMethod1()
	{
		string dbName = Guid.NewGuid().ToString();

		using (var dbContext = new InMemoryMyDbContext(dbName, useRoot))
		{
			var newEntity = new OwningEntity
			{
				Name = "The entity",
				// OwnedA = new OwnedEntity { A = 1, B = "hello" },
				OwnedB = new OwnedEntity { A = 2, B = "goodbye" }
			};

			dbContext.OwningEntities.Add(newEntity);
			await dbContext.SaveChangesAsync();

			var fromDb = dbContext.OwningEntities.Single();
			fromDb.Name.ShouldBe("The entity");
			newEntity.OwnedA.ShouldBeNull();
	   }
	}

	[TestMethod]
	public async Task TestMethod2()
	{
		string dbName = Guid.NewGuid().ToString();

		using (var dbContext = new InMemoryMyDbContext(dbName, useRoot))
		{
			var newEntity = new OwningEntity
			{
				Name = "The entity",
				OwnedA = new OwnedEntity { A = 1, B = "hello" },
				OwnedB = new OwnedEntity { A = 2, B = "goodbye" }
			};

			dbContext.OwningEntities.Add(newEntity);

			await dbContext.SaveChangesAsync();
		}

		using (var dbContext2 = new InMemoryMyDbContext(dbName, useRoot))
		{
			var fromDb = dbContext2.OwningEntities.Single();
			fromDb.Name.ShouldBe("The entity");
		}
	}
}

The whole project is attached to this issue. ef_bug.zip

The first test fails because newEntity.OwnedA that is supposed to stay null has magically gotten the value of OwnedB.

Second test fails with an exception from SaveChangesAsync()

System.ArgumentException: An item with the same key has already been added. Key: 1

The change tracker shows both instances indeed have a key 1, but only when db root is not used the save will succeed:

Further technical details

EF Core version: 3.1.3
Database provider: Microsoft.EntityFrameworkCore.InMemory 3.1.3
Target framework: .NET Core 3.1
Operating system: Windows 10 1909 build 18363.815
IDE: Visual Studio 2019 16.5.4
XUnit 2.4.1, Shouldly 3.0.2

[macwier]

Any chance for this to get merged into 3.x? Or are there any workarounds?

[ajcvickers]

@macwier No. 3.1 is out-of-support.