Rails 3.x — Self-referential has_many :through Parent<->Child relationship modelling

Stamped: 01 Sep 2010 | Show comments

Seriously?

Srsly, that's more of an SEO title than anything, because damnit, I know how the hell it works at an SQL level and it was frustrating to get working in Rails because of syntax, namely :class_name => :object, when it should be :class_name => "object". I hope someone finds this useful, because when it comes to rails 3 there's not too much stuff that's recent.

Get to the point, show me the goods

rails new confusingTitleProject
cd confusingTitleProject
rails g model Person name:string
rails g model PersonRelationship parent_id:integer child_id:integer
#App/Models/PersonRelationship.rb
class PersonRelationship < ActiveRecord::Base
  belongs_to :parent, :class_name => "Person"
  belongs_to :child, :class_name => "Person"
end

#App/Models/Person.rb
class Person < ActiveRecord::Base
  
  validates_presence_of :first_name, :last_name

  has_many     :parent_child_relationships,
               :class_name            => "PersonRelationship",
               :foreign_key           => :child_id,
               :dependent             => :destroy
  has_many     :parents,
               :through               => :parent_child_relationships,
               :source                => :parent

  has_many     :child_parent_relationships,
               :class_name            => "PersonRelationship",
               :foreign_key           => :parent_id,
               :dependent             => :destroy
  has_many     :children,
               :through               => :child_parent_relationships,
               :source                => :child
end

Then, as an example, you can do the following to add a parent:

a = Person.new; b = Person.new
b.parents = [a]
tags: rails, self join, has_many through, habtm
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