EF CTP5 failing to update optional navigation property

Question

I have a many to one association between "Project" and "Template".

Project has a property of type "Template".

The association is not bidirectional ("Template" has no knowledge of "Project").

My entity mapping for the association on "Project" is:

this.HasOptional(p => p.Template);

If I create a "Project" without specifying a template then null is correctly inserted into the "TemplateId" column of the "Projects" table.

If I specify a template then the template's Id is correctly inserted. The SQL generated:

update [Projects]
set    [Description] = '' /* @0 */,
       [UpdatedOn] = '2011-01-16T14:30:58.00' /* @1 */,
       [ProjectTemplateId] = '5d2df249-7ac7-46f4-8e11-ad085c127e10' /* @2 */
where  (([Id] = '8c1b2d30-b83e-4229-b0c3-fed2e36bf396' /* @3 */)
        and [ProjectTemplateId] is null)

However, if I try to change the template or even set it to null, the templateId is not updated. The SQL generated:

update [Projects]
set    [UpdatedOn] = '2011-01-16T14:32:14.00' /* @0 */
where  ([Id] = '8c1b2d30-b83e-4229-b0c3-fed2e36bf396' /* @1 */)

As you can see, TemplateId is not updated.

This just does not make sense to me. I have even tried explicitly setting the "Template" property of "Project" to null in my code and when stepping through the code you can see it has absolutely no effect!

Thanks, Ben

[Update]

Originally I thought this was caused by me forgetting to add the IDbSet property on my DbContext. However, now that I've tested it further I'm not so sure. Below is a complete test case:

public class PortfolioContext : DbContext, IDbContext
{
    public PortfolioContext(string connectionStringName) : base(connectionStringName) { }

    public IDbSet<Foo> Foos { get; set; }
    public IDbSet<Bar> Bars { get; set; }

    protected override void OnModelCreating(System.Data.Entity.ModelConfiguration.ModelBuilder modelBuilder) {

        modelBuilder.Configurations.Add(new FooMap());
        modelBuilder.Configurations.Add(new BarMap());

        base.OnModelCreating(modelBuilder);
    }

    public new IDbSet<TEntity> Set<TEntity>() where TEntity : class {
        return base.Set<TEntity>();
    }
}

public class Foo {
    public Guid Id { get; set; }
    public string Name { get; set; }
    public virtual Bar Bar { get; set; }

    public Foo()
    {
        this.Id = Guid.NewGuid();
    }
}

public class Bar
{
    public Guid Id { get; set; }
    public string Name { get; set; }

    public Bar()
    {
        this.Id = Guid.NewGuid();
    }
}

public class FooMap : EntityTypeConfiguration<Foo>
{
    public FooMap()
    {
        this.ToTable("Foos");
        this.HasKey(f => f.Id);
        this.HasOptional(f => f.Bar);
    }
}

public class BarMap : EntityTypeConfiguration<Bar>
{
    public BarMap()
    {
        this.ToTable("Bars");
        this.HasKey(b => b.Id);
    }
}

And the test:

[Test]  
public void Template_Test()
{
    var ctx = new PortfolioContext("Portfolio");

    var foo = new Foo { Name = "Foo" };
    var bar = new Bar { Name = "Bar" };

    foo.Bar = bar;

    ctx.Set<Foo>().Add(foo);

    ctx.SaveChanges();

    object fooId = foo.Id;
    object barId = bar.Id;

    ctx.Dispose();

    var ctx2 = new PortfolioContext("Portfolio");
    var dbFoo = ctx2.Set<Foo>().Find(fooId);

    dbFoo.Bar = null; // does not update

    ctx2.SaveChanges();
}

Note that this is using SQL CE 4.

Answer 1

Ok, you just need to load the navigation property before doing anything to it. By loading it you essentially register it with ObjectStateManager which EF looks into to generate the update statement as a result of SaveChanges().

using (var context = new Context())
{                
    var dbFoo = context.Foos.Find(fooId);             
    ((IObjectContextAdapter)context).ObjectContext.LoadProperty(dbFoo, f => f.Bar);

    dbFoo.Bar = null;
    context.SaveChanges();
}

This code will result in:

exec sp_executesql N'update [dbo].[Foos]
set [BarId] = null
where (([Id] = @0) and ([BarId] = @1))
',N'@0 uniqueidentifier,@1 uniqueidentifier',@0='A0B9E718-DA54-4DB0-80DA-C7C004189EF8',@1='28525F74-5108-447F-8881-EB67CCA1E97F'