One to one relationship with FK in one direction

Question

How do I get the following relationship to only generate the FK in Entity2?

  public class Entity1
  {
     public int Id { get; set; }

     public virtual Entity2 Entity2 { get; set; }
  }

  public class Entity2
  {
     public int Id { get; set; }

     public int? Entity1Id { get; set; }

     public virtual Entity1 Entity1 { get; set; }
  }

I want Entity1 be able to get a reference to an Entity2 (have EF lazy load it), but I don't want Entity1 to have an FK to Entity2 in the db, I just want Entity2 to have an FK to Entity1. Is this possible? Everything I have been trying in OnModelCreating in my db context isn't getting me what I really want.

The closest I can get is this:

  modelBuilder.Entity<Entity2>().HasOptional(e => e.Entity1).WithOptionalDependent(e => e.Entity2);

However, this will create the Entity2 table with an Entity1Id column AND an Entity1_Id FK column to Entity1, instead of just creating the single Entity1Id column that should be an FK to Entity1.

Also, in case anyone asks, the Entity1Id property is intentionally a nullable int because a Entity2 instance/table record needs to exist independently without a link to Entity1.

Answer 1

Remove the code in OnModelCreating, and add this annotation to your Entity2

public class Entity2
{
 public int Id { get; set; }

 [ForeignKey("Entity1")]
 public int? Entity1Id { get; set; }

 public virtual Entity1 Entity1 { get; set; }

}

Or you can try this (I don't know if it work or not)

modelBuilder.Entity<Entity2>()
.HasOptional(e => e.Entity1)
.WithOptionalDependent(e => e.Entity2)
.Map(m => { m.MapKey("Entity1Id"); });