Entity Framework duplicate composite key values

Question

Using Entity Framework Code First, I'm seeing very strange behavior when inserting a row with a composite key. The composite key consists of a guid ID field and a guid foreign key field, creating an "identifying relationship". The strange behavior is that regardless of what I set the ID and foreign key field to, the generated SQL sets them both to the foreign key value.

My classes look like this:

public class Parent {
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public Guid Id { get; set; }
    public ICollection<Child> Children { get; set; }
}

public class Child {
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public Guid Id { get; set; }
    public Guid ParentId { get; set; }
}

In my DbContext file I have:

modelBuilder.Entity<Child>().HasKey(c => new { c.Id, c.ParentId });

Doing something like:

var parent = new Parent() { Id = Guid.NewGuid() };
var child = new Child() { Id = Guid.NewGuid(), ParentId = parent.Id };
parent.Children.Add(child);

You'd think the SQL executed would insert a new child with differing Id and ParentId values. But instead, what I'm seeing is:

// Assume parent is already in the DB, with ID of '1b1a6ecd-00ad-4265-ac0d-9a50bd30e247'
INSERT [dbo].[Child]
   ([Id],
    [ParentId])
VALUES ('1b1a6ecd-00ad-4265-ac0d-9a50bd30e247' /* @0 */,
    '1b1a6ecd-00ad-4265-ac0d-9a50bd30e247' /* @1 */)

Why is the SQL using the ParentId value for both fields? This doesn't make sense at all.

UPDATE

Unless I totally misunderstand something fundamental to EF, I think this must be a bug. I've uploaded a tiny reproducible project to http://1drv.ms/1kX2oVC

It uses EF 6.1 and .NET 4.5. I'm hoping some EF expert can chime in here and confirm this is a bug, or that I'm doing something fundamentally wrong.

Answer 1

With this set up Entity Framework isn't able to properly infer the associations. You have two options how to fix it:

• Add modelBuilder.Entity<Parent>().HasMany(x => x.Children).WithRequired().HasForeignKey(x => x.ParentId); into your OnModelCreating.

or

• Add public Parent Parent { get; set; } into your Child entity.