bf4/polymorphic_many_to_many_in_rails.md

## polymorphic_many_to_many_in_rails.md

      
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              polymorphic_many_to_many_in_rails.md
            
          
    This was my solution for a polymorphic many-to-many association
class ItemCountry < ActiveRecord::Base
  belongs_to :locatable, :polymorphic => true
  belongs_to :country
  # fields are :locatable_id, :locatable_type, :country_id
end

class Title < ActiveRecord::Base
  has_many :countries, :through => :item_countries, :as => :locatable
  has_many :item_countries, :as => :locatable
end

 class Country < ActiveRecord::Base
   has_many :titles, :through => :item_countries, :source => :locatable, :source_type => 'Title'
   has_many :item_countries, :foreign_key => :country_id
 end

 class CreateItemCountryAssociationTable < ActiveRecord::Migration
   def change
     create_table :item_countries, :id => false do |t|
       t.integer :locatable_id
       t.string  :locatable_type
       t.integer :country_id
     end
     add_index :item_countries, [:locatable_id, :locatable_type, :country_id], :name => 'polymorphic_many_to_many_idx'
     add_index :item_countries, [:locatable_id, :locatable_type], :name => 'polymorphic_locatable_idx'
   end
 end

Now I can do Title.new.countries or Country.new.titles (but not Country.new.items. Country needs to know which polymorphic / locatable item you want. I've only told it about Titles)