删除具有一对一可选关系的实体时出现EntityFramework错误

Question

When I try to delete one entity that is related to another entity by a one-to-one relation with both ends as optional, I have this error:

A relationship from the 'Jury_Slots' AssociationSet is in the 'Deleted' state. Given multiplicity constraints, a corresponding 'Jury_Slots_Target' must also in the 'Deleted' state.

My entities:

public class ApplicantTest
{
    [Key]
    public int Id { get; set; }

    // some other properties

    public virtual JurySlot JurySlot { get; set; }
}

public class JurySlot
{
    [Key]
    public int Id { get; set; }

    // some other properties

    public virtual Jury Jury { get; set; }

    public virtual ApplicantTest ApplicantTest { get; set; }
}

public class Jury
{
    [Key]
    public int Id { get; set; }

    public virtual ICollection<JurySlot> Slots { get; set; }
}

This is how I declared my relation:

modelBuilder.Entity<Jury>()
    .HasMany(j => j.Slots)
    .WithRequired(j => j.Jury);

modelBuilder.Entity<JurySlot>()
    .HasOptional(c => c.ApplicantTest)
    .WithOptionalPrincipal(ec => ec.JurySlot);

What I try to do is (the simplest code to reproduce it): var context = new MyContext();

var existing = context.Jurys.Include(j => j.Slots.Select(c => c.ApplicantTest)).Single(j => j.Id == 5);
var lastSlot = existing.Slots.First(c => c.ApplicantTest != null);

// does not work #1
//lastSlot.ApplicantTest = null;

// does not work #2
//context.Entry(lastSlot.ApplicantTest).State = EntityState.Modified;
//lastSlot.ApplicantTest.JurySlot = null;
//lastSlot.ApplicantTest = null;

existing.Slots.Remove(lastSlot);

// exception thrown...
context.SaveChanges();

Before the call to Remove(), I tried the things that are commented, but without success...

Does anybody have an idea?

Answer 1

Can't explain why (I guess one of the little EF mysteries), but deleting from the corresponding DbSet does the trick:

...

//existing.Slots.Remove(lastSlot);
context.JurySlots.Remove(lastSlot);

context.SaveChanges();

executes the following commands:

UPDATE [dbo].[ApplicantTests]
SET [JurySlot_Id] = NULL
WHERE (([Id] = @0) AND ([JurySlot_Id] = @1))

DELETE [dbo].[JurySlots]
WHERE (([Id] = @0) AND ([Jury_Id] = @1))