# File lib/active_record/associations.rb, line 1044
      def has_and_belongs_to_many(association_id, options = {}, &extension)
        reflection = create_has_and_belongs_to_many_reflection(association_id, options, &extension)

        add_multiple_associated_validation_callbacks(reflection.name) unless options[:validate] == false
        add_multiple_associated_save_callbacks(reflection.name)
        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\ndef destroy_without_callbacks\n\#{reflection.name}.clear\n\#{old_method}\nend\n" unless method_defined?(old_method)

        add_association_callbacks(reflection.name, options)
      end