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.

i think it should ICollection in your class User, and you can put the RelationTypeId in followers class where RelationTypeId is referencing a look up entity RelationType( Id, Name) where Name = Follower or Following, if you want i can show you exmaple — Monah, Jul 19 '15 at 09:58
check my answer below, if you need more help ask, hope it will help you — Monah, Jul 19 '15 at 11:25
Thanks for posting. Is this correct way to do this? I mean there will be thousands of rows with many user! — Hamza Baig, Jul 19 '15 at 11:28
in my opinion Yes it is, if you look to the result, it obeys the normalization rules, also i added sample how to get the user followers and who the user is following — Monah, Jul 19 '15 at 11:31
the solution i provided is called 1-to-many, you might make many-to-many solution but this will cost you more as maintaining your code and in queries, if you want i can post many-to-many solution also — Monah, Jul 19 '15 at 11:34

ycsun · Answer 1 · 2015-07-20T03:06:47.347

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).

Thank you for your answer. But how entity framework will know that which are followers and which are following? — Hamza Baig, Jul 19 '15 at 11:14

Monah · Answer 2 · 2015-07-19T17:35:44.667

based on your requirements, you can do the following:

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

public enum EFollowerType
{
    Follower=1,
    Following
}

public class Follower
{
  public int Id { get;  set; }
  public int UserId { get; set; }
  public int FollowedById { get; set; }
  public EFollowerType FollowerType { get; set; }

  public User User { get; set; }
  public User FollowedBy { get; set; }
}

//in the OnModelCreating function in the DbContext 

modelBuilder.Entity<Follower>()
            .HasRequired(m=> m.User)
            .WithMany(m=> m.Followers)
            .HasForeignKey(k=> k.UserId);
modelBuilder.Entity<Follower>()
            .HasRequired(m=> m.FollowedBy)
            .WithMany(m=> m.Following)
            .HasForeignKey(k=> k.FollowedById);

//to add a follower 
var user = ... user details goes here ... 
var follower = new Follower(){
   FollowerType = FollowerType.Follower, // if you want it as Follower
   User = user,
};
db.Followers.Add(follower);
db.SaveChanges();

// to know how many followers the user has

var followers = user.Followers.Count(t=>t.FollowerType ==EFollowerType.Follower);

// to know how many the user is following 
var following = user.Followers.Count(t=>t.FollowerType ==EFollowerType.Following);

you also can make FollowerType as a table if you want for example to make multilingual database or you want to add other types of Followers without modifying your code ( enum )

hope this will help you

you are right i missed the Follower User in the table Follower i will edit the answer — Monah, Jul 19 '15 at 14:31
@HamxaBaig kindly check the edited answer now, hope it will help you — Monah, Jul 19 '15 at 17:36
i like this approach better, no shadow tables that nobody is aware of — darren z, Sep 24 '21 at 23:33

score 0 · Answer 3 · answered Nov 07 '16 at 20:09

0

You can Simply use :

modelBuilder.Entity<User>().HasMany(m => m.Followers).WithMany(m=>m.Following ).Map(x => x.MapLeftKey("Id").MapRightKey("FollowerId").ToTable("Followers"));

answered Nov 07 '16 at 20:09

Karvan

250
2
7

Followers Schema in Entity Framework

3 Answers3

Update

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