define_destroy_hook

# File activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb, line 27
    def define_destroy_hook
      name = self.name
      model.send(:include, Module.new {
        class_eval           def destroy_associations            association(:#{name}).delete_all            super          end, __FILE__, __LINE__ + 1
      })
    end