Rails Ruby on Rails

In the case of a has_many :through relationship, which also happens to be polymorphic in both directions, the after_add callback gets executed for both the direct relationship and the through relationship. It seems like there is an inconsistency though, as the after_remove callback only gets executed on the direct relationship and not the through relationship. This is best shown by the following example where there are polymorphic types Locations and People. User being and instance of Person and Address being an instance of Location.

# location_person.rb
class LocationPerson < ActiveRecord::Base
  belongs_to :location, :polymorphic => true
  belongs_to :person, :polymorphic => true
end

# address.rb
class Address < ActiveRecord::Base
  has_many :people, :as => :location, :class_name => "LocationPerson"
end

# user.rb
class User < ActiveRecord::Base
  has_many :locations, :as => :person, :class_name => "LocationPerson", :after_remove => :remove_location_point, :after_add => :add_location_point
  has_many :addresses, :through => :locations, :source => :location, :source_type => "Address", :after_remove => :remove_address_point, :after_add => :add_address_point

  def remove_location_point(location)
    puts "Removing Location Point"
  end

  def remove_address_point(address)
    puts "Removing Address Point"
  end

  def add_location_point(location)
    puts "Adding Location Point"
  end

  def add_address_point(address)
    puts "Adding Address Point"
  end
end

Call the following in console to demonstrate the asymetry:

ruby-1.8.7-p302 > user = User.create
 => #<User id: 2, created_at: "2010-12-22 15:44:14", updated_at: "2010-12-22 15:44:14"> 
ruby-1.8.7-p302 > addr = Address.create
 => #<Address id: 2, created_at: "2010-12-22 15:44:23", updated_at: "2010-12-22 15:44:23"> 
ruby-1.8.7-p302 > user.addresses << addr
Adding Location Point
Adding Address Point
 => [#<Address id: 2, created_at: "2010-12-22 15:44:23", updated_at: "2010-12-22 15:44:23">] 
ruby-1.8.7-p302 > user.addresses = []
Removing Address Point
 => []

As you can see, "Adding Location Point" and "Adding Address Point" were both printed indicating both after_add callbacks were executed. However only "Removing Address Point" was printed indicating that the after_remove callback on the :locations relationship was never called.