Self-referencing many-to-many recursive relationship code first Entity Framework

Question

I can't seem to make this work at all

class Member
{
    public virtual IList<Member> Friends { get; set; }
    [Key]
    public int MemberId { get; set; }
    public string Name{ get; set; }
}

I tried adding Mappings but in vain. Is there a way to do so with CTP5?

Answer 1

By convention, Code First will take uni-directional associations as one to many. Therefore you need to use fluent API to let Code First know that you want to have a many to many self referencing association:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Member>().HasMany(m => m.Friends).WithMany();
}

Note: There is a known bug in CTP5 that won't let you customize the join table column names in this scenario.

Answer 2

If I am correct you can influence the many to many table name with this code:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Member>().HasMany(m => m.Friends).WithMany().Map(m =>
        {
            m.MapLeftKey("MemberId");
            m.MapRightKey("FriendId");
            m.ToTable("MembersFriends");
        }
    );
}

hope this helps.

Answer 3

You can get this to work in EF 4 CTP5 using Model-First, but the CTP5 Code First has too many bugs with self-referential and polymorphic query configurations to use Code First for such scenarios. Morteza Manavi (see other answer) has documented several of them on his blog.

Answer 4

Your example is not a many-to-many relationship, it is more of a recursive relationship.

I am not sure how to fix it. But the problem with your code is that your will get two fields on the same row with the same name. MemberId for the id of the row and MemberId for the id of the friend.

Edit

Try doing it like this:

    class Member 
    { 
        [Key]
        public int MemberId { get; set; } 
        public string Name { get; set; }

        public virtual IList<FriendRelationship> Friends { get; set; } 

    }

    class FriendRelationship
    {
        [Key]
        public int RelationshipId { get; set; }

        public Member Friend { get; set; }
    }