Reputation: 881
I want to self-referentiate a model in a RoR app but, I don't know exactly how. I want to save a linked list where the next node has the id of the previous one. how can I do this rails way? It is a one-to-one relation.
Upvotes: 36
Views: 36761
Reputation: 720
rails 5
add column xxx_id in users table:
in migration file:
add_reference :users, :xxx, index: true
and add code in User model
has_many :users, class_name: 'User', foreign_key: 'xxx_id'
belongs_to :manager, class_name: 'User', foreign_key: 'xxx_id'
If you don't have a manager for every user, you need to add optional: true.
'foreign_key' is not necessary. By default this is guessed to be the name of this class in lower-case and “_id” suffixed.
if foreign_key is user_id, user don't have manager necessary. the result is:
has_many :users, class_name: 'User'
belongs_to :manager, class_name: 'User', optional: true
They are called self-joins
Upvotes: 31
Reputation: 8833
I've spent some time trying to make it work using Rails 3.2.14
The documentation's suggestion for self-joining associations hasn't worked for belongs_to
associations. Adding a foreign key fixed the issue.
Class User < ActiveRecord::Base
has_many :invitees, class_name: 'User', foreign_key: :invited_by
belongs_to :host, class_name: 'User', foreign_key: :invited_by
end
Upvotes: 3
Reputation: 9167
The easiest way:
class MyModel < ActiveRecord::Base
belongs_to :parent, :class_name => 'MyModel'
has_many :children, :class_name => 'MyModel', :foreign_key => 'parent_id'
end
Upvotes: 85