Ruby On Rails--Active Record Associations（关联关系）

阳光穿透心脏的1/2处 2022-07-26 05:08 6阅读 0赞

> Why do we need associations between models? Because they make common operations simpler and easier in your code.

## Active Record Associations知识总览 ##

[官方文档][Link 1]

## 为什么使用Associations ? ##

## Associations的类型 ##

*  belongs\_to
 *  has\_one
 *  has\_many
 *  has\_many :through
 *  has\_one :through
 *  has\_and\_belongs\_to\_many
 *  如何判断选择belongs\_to还是has\_one
 *  如何判断选择has\_many :through 还是 has\_and\_belongs\_to\_many
 *  Polymorphic Associations（多态关联, :polymorphic, :as）
 *  Self Joins(自关联)

## 注意事项 ##

*  Controlling caching(控制缓存)
 *  Avoiding name collisions(避免命名冲突)
 *  Updating the schema(更新数据库表结构)  
    
    
     *  为belongs\_to创建外键
     *  为has\_and\_belongs\_to\_many创建关联表(中间表)
 *  Controlling association scope(控制关联的scope，必要时需要使用:class\_name参数)
 *  Bi-directional associations(双向关联,多份对象拷贝可能导致数据不同步，:inverse\_of参数)

## 各个关联关系详解 ##

### belongs\_to详解 ###

*  belongs\_to 添加了哪些方法  
    
    
     *  association(force\_reload = false)
     *  association=(associate)
     *  build\_association(attributes = \{\})
     *  create\_association(attributes = \{\})
     *  create\_association!(attributes = \{\})
 *  belongs\_to 有哪些可选参数  
    
    
     *  :autosave
     *  :class\_name
     *  :counter\_cache
     *  :dependent
     *  :foreign\_key
     *  :inverse\_of
     *  :polymorphic
     *  :touch
     *  :validate
 *  belongs\_to 的scopes  
    
    
     *  where
     *  includes
     *  readonly
     *  select
 *  判断关联对象是否存在: association.nil? 方法
 *  关联对象何时被保存

### has\_one 详解 ###

*  has\_one 添加了哪些方法  
    
    
     *  association(force\_reload = false)
     *  association=(associate)
     *  build\_association(attributes = \{\})
     *  create\_association(attributes = \{\})
     *  create\_association!(attributes = \{\})
 *  has\_one 有哪些可选参数  
    
    
     *  :as
     *  :autosave
     *  :class\_name
     *  :dependent
     *  :foreign\_key
     *  :inverse\_of
     *  :primary\_key
     *  :source
     *  :source\_type
     *  :through
     *  :validate
 *  判断关联对象是否存在: association.nil? 方法
 *  关联对象何时被保存

### has\_many 详解 ###

*  has\_many 添加了哪些方法  
    
    
     *  collection(force\_reload = false)
     *  collection<<(object, …)
     *  collection.delete(object, …)
     *  collection.destroy(object, …)
     *  collection=(objects)
     *  collection\_singular\_ids
     *  collection\_singular\_ids=(ids)
     *  collection.clear
     *  collection.empty?
     *  collection.size
     *  collection.find(…)
     *  collection.where(…)
     *  collection.exists?(…)
     *  collection.build(attributes = \{\}, …)
     *  collection.create(attributes = \{\})
     *  collection.create!(attributes = \{\})
 *  has\_many 有哪些可选参数  
    
    
     *  :as
     *  :autosave
     *  :class\_name
     *  :dependent
     *  :foreign\_key
     *  :inverse\_of
     *  :primary\_key
     *  :source
     *  :source\_type
     *  :through
     *  :validate
 *  has\_many 可用的 scopes  
    
    
     *  where
     *  extending
     *  group
     *  includes
     *  limit
     *  offset
     *  order
     *  readonly
     *  select
     *  uniq
 *  关联对象何时被保存

### has\_and\_belongs\_to\_many 详解 ###

*  has\_and\_belongs\_to\_many 添加了哪些方法  
    
    
     *  collection(force\_reload = false)
     *  collection<<(object, …)
     *  collection.delete(object, …)
     *  collection.destroy(object, …)
     *  collection=(objects)
     *  collection\_singular\_ids
     *  collection\_singular\_ids=(ids)
     *  collection.clear
     *  collection.empty?
     *  collection.size
     *  collection.find(…)
     *  collection.where(…)
     *  collection.exists?(…)
     *  collection.build(attributes = \{\})
     *  collection.create(attributes = \{\})
     *  collection.create!(attributes = \{\})
 *  has\_many 有哪些可选参数  
    
    
     *  :association\_foreign\_key
     *  :autosave
     *  :class\_name
     *  :foreign\_key
     *  :join\_table
     *  :validate
 *  has\_many 可用的 scopes  
    
    
     *  where
     *  extending
     *  group
     *  includes
     *  limit
     *  offset
     *  order
     *  readonly
     *  select
     *  uniq
 *  关联对象何时被保存

## Association Callbacks(关联Callbacks) ##

*  before\_add
 *  after\_add
 *  before\_remove
 *  after\_remove

## Association Extensions(关联扩展, extending) ##

[Link 1]: http://guides.rubyonrails.org/association_basics.html