Self join in active record association
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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.
Self join in active record association
- 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.