Question

I’ve read lots about self referential classes in Rails, but am still having problems getting them working.

I have a class of Articles and I want them to be able to refer to each other, from a source article to an outcome article – and then be able to find the reverse. So I’m trying to do a has_many through, using another class called Links.

My schema is

  create_table "articles", :force => true do |t|
    t.string   "name"
    t.text     "body"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "links", :force => true do |t|
    t.integer  "source_id"
    t.integer  "outcome_id"
    t.string   "question"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

The models are

class Article < ActiveRecord::Base
    has_many :links_as_source, :foreign_key => "source_id", :class_name => "Link"
    has_many :sources, :through => :links_as_source

    has_many :links_as_outcome, :foreign_key => "outcome_id", :class_name => "Link"
    has_many :outcomes, :through => :links_as_outcome
end

and

class Link < ActiveRecord::Base
    belongs_to :source, :foreign_key => "source_id", :class_name => "Article"
    belongs_to :outcome, :foreign_key => "outcome_id", :class_name => "Article"
end

I can create articles in the console, and I can link articles together, using a.outcomes << b but the link table is only storing the outcome_id, not the source_id.

What am I doing wrong?

Answer 1

I got this to work in the end. I changed the names – I don’t know if that mattered. I did read somewhere that source was a silly name to use for something.

So this is what works:

My schema

create_table "article_relationships", :force => true do |t|
  t.integer  "parent_id"
  t.integer  "child_id"
  ...
end

create_table "articles", :force => true do |t|
  t.string   "name"
  ...
end

My article model

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

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