Followers Schema in Entity Framework

Question

I am making an App which will have the Following functionality. But I am stuck at this. I have come up like this.

public class User
{
  public int Id { get; set; }
  public ICollection<User> Followers { get; set; }
  public ICollection<User> Following { get; set; }
}

And the followers table will be

public class Followers
{
public int UserId { get; set; }
public int FollowerId { get; set; }
}

But in this approach how will Entity framework will know that which are Followers and which I am following? Thanks in Advance.

Answer 1

Looks like you want a many-to-many self-referencing relationship using code first? You don't need the Followers class. Just define the User class:

public class User
{
  public int Id { get; set; }
  public ICollection<User> Followers { get; set; }
  public ICollection<User> Following { get; set; }
}

and then write your DbContext class this way:

public class MyEntities: DbContext
{
  public DbSet<User> Users { get; set; }

  protected override void OnModelCreating(DbModelBuilder modelBuilder)
  {
    modelBuilder.Entity<User>()
        .HasMany(x => x.Followers).WithMany(x => x.Following)
        .Map(x => x.ToTable("Followers")
            .MapLeftKey("UserId")
            .MapRightKey("FollowerId"));
  }
}

A Followers table will be created in the database along with the Users table. You can test it with the following code:

using (var db = new MyEntities()) {
  var user1 = new User();
  var user2 = new User();
  var user3 = new User();
  user1.Followers = new User[] { user2 };
  user2.Followers = new User[] { user3 };
  db.Users.Add(user1);
  db.SaveChanges();
}

Update

How Entity Framework knows which are followers and which are following? The answer is, it interprets the modelBuilder statement this way:

• Entity<User>: the subject is User;
• HasMany(x => x.Followers): a user has many followers;
• WithMany(x => x.Following): each follower has many following;
• Map(...): the link table is Followers, the left key points to the subject (user), the right key points to the subject's related entity (follower).