Nested Has Many Through
This plugin makes it possible to define has_many :through relationships that go through other has_many :through relationships, possibly through an arbitrarily deep hierarchy. This allows associations across any number of tables to be constructed, without having to resort to find_by_sql (which isn’t a suitable solution if you need to do eager loading through :include as well).
It is hoped that this feature will in time be applied to the Rails core, after which this plugin will become unnecessary. See: http://dev.rubyonrails.org/ticket/6461
Example
class Pub < ActiveRecord::Base belongs_to :city end
class City < ActiveRecord::Base belongs_to :country has_many :pubs end
class Country < ActiveRecord::Base belongs_to :planet has_many :cities has_many :pubs, :through => cities end
class Planet < ActiveRecord::Base belongs_to :star_system has_many :countries has_many :cities, :through => :countries end
- Now we go through a has_many :through association -
- something that wasn’t previously possible has_many :pubs, :through => :cities
class StarSystem < ActiveRecord::Base has_many :planets has_many :countries, :through => :planets end
- We can also use a has_many :through association for the source
- association; in this case, Country#pubs has_many :pubs, :through => countries
NOTE: This description has been extracted from the Plugin README and so the formatting may need updating to make browser friendly
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