Entity Framework cardinality in a 1..1 or 1..0 relationship

Question

I have an entity which has a self reference such that a Member can have a Witness who has to be a member and may also have a Reference who has to be a member. I modeled this as follows;

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

        //omitted for brevity
        public int? WitnessId { get; set; }
        public virtual Member Witness { get; set; }

        public int? ReferenceId { get; set; }
        public virtual Member Reference { get; set; }
    }

When I run the update-database on package manager console, I get the following error: "XXX.Client.Entities.Member' and 'XXX.Client.Entities.Member'. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations."

Any idea on how this can be resolved?

Answer 1

Try to define relationship with fluent api this way (works for me):

        modelBuilder.Entity<Member>().HasKey(x => x.Id);
        modelBuilder.Entity<Member>().HasOptional(x => x.Witness)
            .WithMany()
            .HasForeignKey(m => m.WitnessId);
        modelBuilder.Entity<Member>().HasOptional(x => x.Reference)
            .WithMany()
            .HasForeignKey(m => m.ReferenceId);

Answer 2

This looks to be working:

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {


        modelBuilder.Entity<Member>().
            HasOptional(e => e.Witness).
            WithMany().
            HasForeignKey(m => m.WitnessID);

        modelBuilder.Entity<Member>().
            HasOptional(e => e.Reference).
            WithMany().
            HasForeignKey(m => m.ReferenceID);

        base.OnModelCreating(modelBuilder);

    }

Answer 3

This will also work for those of us who prefer to have things in the class deriving from the EntityTypeConfiguration

class MemberEntityConfiguration : EntityTypeConfiguration<Member>
{
    public MemberEntityConfiguration()
    {
        HasKey(x => x.Id);
        HasOptional(x => x.Witness).WithMany().HasForeignKey(m => m.WitnessId);
        HasOptional(x => x.Reference).WithMany().HasForeignKey(m => m.ReferenceId);
    }
}