Adding new Methods to your association for advanced queries

You're not limited to the functionality that Rails automatically builds into association proxy objects. You can also extend these objects through anonymous modules, adding new finders, creators, or other methods. For example:

class Customer < ActiveRecord::Base  has_many :orders do 

   def find_customer_by_order_id(order_id)
     o=Order.find(order_id)
     o.customer
   end 

  end
end

now in console:

>>c=Customer.first

 #<Customer id: 1, name: "ttttttttttt", created_at: "2015-04-29 12:30:13", updated_at: "2015-05-05 10:36:06", orders_count: 1> 

>>c.orders.find_customer_by_order_id(2)

 #<Customer id: 1, name: "ttttttttttt", created_at: "2015-04-29 12:30:13", updated_at: "2015-05-05 10:36:06", orders_count: 1>  







If you have an extension that should be shared by many associations, you can use a named extension module. For example:

module FindRecentExtension

  def find_recent

    where("created_at > ?", 5.days.ago)

  end

end

class Customer < ActiveRecord::Base

  has_many :orders, -> { extending FindRecentExtension }

end

class Supplier < ActiveRecord::Base

  has_many :deliveries, -> { extending FindRecentExtension }

end