A dependent property in a ReferentialConstraint is mapped to a store-generated column. Column 'Id' in TPT inheritance

Question

I'm using EF code first, I have following entities:

I'm using TPT method for inheritance, to create one-to-one or zero relation, wrote following code:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Order>()
                .HasOptional(x => x.ProductionInstruction)
                .WithRequired(x => x.Order);
}

I write following code to save a ProductionInstruction:

var pi = new ProductionInstruction();
/* set pi properties */
ctx.ProductionInstructions.Add(pi);
ctx.SaveChanges();

I get following error when ctx.SaveChanges() run:

A dependent property in a ReferentialConstraint is mapped to a store-generated column. Column: 'Id'.

Is there any way to implement 1..0-1 between my two entities, without above error?

Answer 1

In Entity Framework, a one-to-one mapping with a required principal is implemented by giving the dependent a primary key that's also a foreign key to the principal. The dependent copies its primary key from the principal.

In your case, EF wants ProductionInstruction.Id to be a foreign key to Order.Id, and its value should be copied from the Order it belongs to. However, because of the inheritance, ProductionInstruction.Id is an identity column (store-generated), so it can't be set in code.

You either have to remove the inheritance, so ProductionInstruction.Id can be mapped as not store-generated, or change the mapping to optional on both sides. The latter will give ProductionInstruction a separate foreign key to Order.