Question

I have two entities referenced one to many. When entity framework created the table it creates two foreign keys, one for the key I have specified with the fluent interface and the other for the ICollection. How do I get rid of the duplicate foreign key?

public class Person
{
    public long RecordId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
    public string Username { get; set; }

    public long DepartmentId { get; set; }
    public virtual Department Department { get; set; }
}

public class Department
{
    public long RecordId { get; set; }
    public string Name { get; set; }

    public virtual ICollection<Person> People { get; set; }
}

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Person>()
        .HasRequired(p => p.Department)
        .WithMany()
        .HasForeignKey(p => p.DepartmentId)
        .WillCascadeOnDelete(false);
}

Thanks!

Answer 1

You must specify the many-end of the association explicitely:

modelBuilder.Entity<Person>()
    .HasRequired(p => p.Department)
    .WithMany(d => d.People)
    .HasForeignKey(p => p.DepartmentId)
    .WillCascadeOnDelete(false);

Otherwise EF will assume that there are two associations: One which is not exposed in Department with the foreign key DepartmentId and navigation property Department in the Person class as you have defined in the Fluent code – and another association which belongs to the exposed navigation property People but with another not exposed end in Person and a foreign key automatically created by EF. That’s the other key you see in the database.