The document discusses setting up a self-join association in Rails using ActiveRecord. It generates a User model and users_friends join table, defines a has_and_belongs_to_many association between the User model and itself, and includes a method to check if a user is friends with another user by checking if their ID is included in the friend_ids array.

1. Active Record Association
Self-Join
Ror lab.
- Speicial episode -
August 1st, 2013
Hyoseong Choi

2. User Model
class User < ActiveRecord::Base
has_and_belongs_to_many :friends,
class_name: 'User',
foreign_key: 'friend_id',
association_foreign_key: 'user_id',
join_table: 'users_friends'
def is_friend_of?(user_id)
friend_ids.include? user_id
end
end

3. ‘users’ table
$ rails g model User name
$ rake db:migrate
== CreateUsers: migrating ===============================
-- create_table(:users)
-> 0.0062s
== CreateUsers: migrated (0.0062s) ======================

4. ‘users_friends’ table
$ rails g migration create_join_table user:references
friend:references
class CreateJoinTable < ActiveRecord::Migration
def change
create_table :users_friends do | t |
t.references :user, index: true
t.references :friend, index: true
t.timestamps
end
end
end
$ rake db:migrate
== CreateJoinTable: migrating ===============================
-- create_table(:users_friends)
-> 0.0035s
== CreateJoinTable: migrated (0.0035s) ======================

5. User Friend
UsersFriend
class User < ActiveRecord::Base
has_and_belongs_to_many :friends
end
class Friend < ActiveRecord::Base
has_and_belongs_to_many :users
end
class UsersFriend < ActiveRecord::Base
belongs_to :user
belongs_to :friend
end
has_and_belongs_to_many

6. User User
UsersFriend
class UsersFriend < ActiveRecord::Base
belongs_to :user
belongs_to :friend
end
has_and_belongs_to_many
class User < ActiveRecord::Base
has_and_belongs_to_many :friends,
class_name: ‘User’,
foreign_key: ‘friend_id’
association_foreign_key: ‘user_id’
end
self join

7. 감사합니다.