add_destroy_callbacks

# File activerecord/lib/active_record/associations/builder/belongs_to.rb, line 110
    def self.add_destroy_callbacks(model, reflection)
      if reflection.deprecated?
        # If :dependent is set, destroying the record has some side effect that
        # would no longer happen if the association is removed.
        model.before_destroy do
          report_deprecated_association(reflection, context: ":dependent has a side effect here")
        end
      end

      model.after_destroy lambda { |o| o.association(reflection.name).handle_dependency }
    end