has_and_belongs_to_many (ActiveRecord::Associations::ClassMethods)

    # File lib/active_record/associations.rb, line 1206
          def has_and_belongs_to_many(association_id, options = {}, &extension)
            reflection = create_has_and_belongs_to_many_reflection(association_id, options, &extension)
            collection_accessor_methods(reflection, HasAndBelongsToManyAssociation)

            # Don't use a before_destroy callback since users' before_destroy
            # callbacks will be executed after the association is wiped out.
            old_method = "destroy_without_habtm_shim_for_#{reflection.name}"
            class_eval "alias_method :\#{old_method}, :destroy_without_callbacks  # alias_method :destroy_without_habtm_shim_for_posts, :destroy_without_callbacks\ndef destroy_without_callbacks                            # def destroy_without_callbacks\n\#{reflection.name}.clear                               #   posts.clear\n\#{old_method}                                          #   destroy_without_habtm_shim_for_posts\nend                                                      # end\n" unless method_defined?(old_method)

            add_association_callbacks(reflection.name, options)
          end