Ruby on Rails 回调，:before_save 和:before_create 之间有什么区别？

Ruby on Rails Callback, what is difference between :before_save and :before_create?

提问by Agung Prasetyo

Could you explain in detail what the :before_saveand :before_createRuby on Rails callbacks are, and what they have to do with Rails validations? Does validation occur after :before_saveor :before_create?

能不能详细解释一下什么是:before_save和:before_createRuby on Rails的回调是，他们有使用Rails验证该怎么办？验证是否发生在:before_save或之后:before_create？

回答by Chowlett

In a create operation under Rails, there are six callbacks before the database operation, and two after. In order, these are:

在 Rails 下的创建操作中，数据库操作之前有六个回调，之后有两个。按顺序，这些是：

1. before_validation
2. before_validation_on_create
3. after_validation
4. after_validation_on_create
5. before_save
6. before_create
   
   DATABASE INSERT
7. after_create
8. after_save

1. before_validation
2. before_validation_on_create
3. after_validation
4. after_validation_on_create
5. before_save
6. before_create
   
   数据库插入
7. after_create
8. after_save

Update operations have exactly the same set, except read updateinstead of createeverywhere (and UPDATEinstead of INSERT).

更新操作具有完全相同的设置，除了读取update而不是create无处不在（以及UPDATE而不是INSERT）。

From this, you can see that validation is carried out before the before_saveand before_createcallbacks.

由此可以看出，验证是在before_save和before_create回调之前进行的。

The before_saveoccurs slightly before the before_create. To the best of my knowledge, nothing happens between them; but before_savewill also fire on Update operations, while before_createwill only fire on Creates.

在before_save之前的略微发生before_create。据我所知，他们之间什么也没有发生。但before_save也会触发更新操作，而before_create只会触发创建。

回答by Michael Koper

before_saveis called every time an object is saved. So for new and existing objects. (create and update action)

before_save每次保存对象时都会调用。所以对于新的和现有的对象。（创建和更新操作）

before_createonly before creation. So only for new objects (create action)

before_create仅在创建之前。所以仅适用于新对象（创建操作）

回答by 23inhouse

before_createvs before_save :on => :create

before_create对比 before_save :on => :create

Sometimes you have to be careful of the order of the callbacks

有时你必须注意回调的顺序

See here for more details: http://pivotallabs.com/activerecord-callbacks-autosave-before-this-and-that-etc/

有关更多详细信息，请参见此处：http: //pivotallabs.com/activerecord-callbacks-autosave-before-this-and-that-etc/