text: ALTER TABLE `conversation_user` 
  DROP FOREIGN KEY `fk_conversation_user_1`,
  DROP FOREIGN KEY `fk_conversation_user_2`;
  ALTER TABLE `conversation_user` 
  ADD CONSTRAINT `fk_conversation_user_1`
    FOREIGN KEY (`conversation_id`)
    REFERENCES `conversation` (`id`)
    ON DELETE CASCADE
    ON UPDATE NO ACTION,
  ADD CONSTRAINT `fk_conversation_user_2`
    FOREIGN KEY (`user_id`)
    REFERENCES `user` (`id`)
    ON DELETE CASCADE
    ON UPDATE NO ACTION;
  
  