你可以通过 :dependent =>has_many 调用的 :restrict 选项:

You can pass the :dependent => :restrict option to your has_many calls:

has_many :models, :dependent => :restrict

这样，只有在没有其他关联对象引用它的情况下，您才能销毁该对象.

This way, you will only be able to destroy the object if no other associated objects reference it.

其他选项是:

• :destroy - 销毁所有调用其 destroy 方法的关联对象.
• :delete_all - 删除所有关联对象调用它们的 destroy 方法.
• :nullify - 将关联对象的外键设置为 NULL 无需调用它们的保存回调.

• :destroy - destroys every associated object calling their destroy method.
• :delete_all - deletes every associated object without calling their destroy method.
• :nullify - sets the foreign keys of the associated objects to NULL without calling their save callbacks.