Many to Many Relationship with One Model

rubyonrails-talk
1

Hey everyone,

I'm working on allow users to follow other users in my app so they can receive updates to what all their friends are doing (like Facebook/ Twitter). I'm wondering on how the relationship would be for the model. Sounds like a HABTM type of association, but how would I go about doing it for only one model?

Thanks, Tony

2

I’ll start w/ the User class.

class User < ActiveRecord::Base has_and_belongs_to_many :friends, :class_name => “User”, # [1] :join_table => “users_friends”, # [2]

:foreign_key => "user_id", # [3]
:association_foreign_key => "friend_id" # [4]

end

[1] Specify the class name since it differs from the association name. [2] Specify the join table since you’ll name it something other than users_users, which is what Rails would assume.

[3] Specify the foreign key back to this user; not necessary as Rails will assume it in this case, but I thought I’d show it. [4] Specify the foreign key that will hold the ids of this user’s friends.

Here’s the migration to create the join table.

class … < ActiveRecord::Migration def self.up create_table :users_friends, :id => false, :force => true do |t| t.integer :user_id, t.integer :friend_id end end

def self.down drop_table :users_friends end end

As you can see, it’s just a simple join table for tracking the relationship from user to user (friend).

I’m sure you’ll want to tweak the User class and migration a bit, but I hope you get the idea.

Regards, Craig

3

That's exactly was I was trying to pull off, perfect explanation!

Thanks a lot Craig!

4

I agree, I was trying to figure out how to do exactly the same thing! Great explanation.