删除具有一对一可选关系的实体时出现EntityFramework错误

Question

当我尝试通过一对一的关系删除一个与另一个实体相关的实体时，两端都是可选的，我有这个错误：

来自'Jury_Slots'AssociationSet的关系处于'已删除'状态。 给定多重约束，相应的'Jury_Slots_Target'也必须处于'已删除'状态。

我的实体：

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; }
}

这就是我宣布我的关系的方式：

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

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

我尝试做的是（最简单的代码来重现它）：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();

在调用Remove（）之前，我尝试了评论的内容，但没有成功......

有人有想法吗？

Answer 1

无法解释为什么（我猜其中一个小EF的谜团），但从相应的DbSet中删除可以DbSet问题：

...

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

context.SaveChanges();

执行以下命令：

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

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