Active Record Nested Attributes通过嵌套属性(nested attribute),你可以通过parent来保存与其相关联的属性。默认情况下,嵌套属性是关闭的,你可以开启accepts_nested_attributes_for这个类方法,就在该model上生成一个属性writer。属性writer是以该关联命名。例如,为你的model增加两个新方法:author_attributes=(attributes) 和 pages_attributes=(attributes).使用了accepts_nested_attributes_for的每一个关联都自动开启:autosaveRuby代码
- class Book < ActiveRecord::Base
- has_one :author
- has_many :pages
- accepts_nested_attributes_for :author, :pages
- end
一对一关联
一个Member有一个Avatar开启一对一关联的嵌套属性可以通过这样方法一次性创建Member:Ruby代码
- class Member < ActiveRecord::Base
- has_one :avatar
- accepts_nested_attributes_for :avatar
- end
默认情况下你只能设置或更新关联的model。如果你想通过属性hash来删除关联model,你需要使用:allow_destroy 选项Ruby代码
- params = { :member => { :name => 'Jack', :avatar_attributes => { :icon => 'smiling' } } }
- member = Member.create(params[:member])
- member.avatar.id # => 2
- member.avatar.icon # => 'smiling'
- 也可以这样update avatar
- params = { :member => { :avatar_attributes => { :id => '2', :icon => 'sad' } } }
- member.update_attributes params[:member]
- member.avatar.icon # => 'sad'
此时,如果向属性hash里增加一个_destroy的key,并且value是true,则该关联model将被删除。Ruby代码
- class Member < ActiveRecord::Base
- has_one :avatar
- accepts_nested_attributes_for :avatar, :allow_destroy => true
- end
注意这里,只有当parent被保存后,关联的model才真正被删除。Ruby代码
- member.avatar_attributes = { :id => '2', :_destroy => '1' }
- member.avatar.marked_for_destruction? # => true
- member.save
- member.reload.avatar # => nil
一对多关联
一个member有一些post你可通过属性hash来增加或更新关联post model每一个不含有id键的新记录会被实例化,除非该hash也包含了一个 :_destroy => trueRuby代码
- class Member < ActiveRecord::Base
- has_many :posts
- accepts_nested_attributes_for :posts
- end
通过 :reject_if proc 设置忽略的不满足条件的记录。例如:Ruby代码
- params = {
- :member => {
- :name => 'joe', :posts_attributes => [
- { :title => 'Kari, the awesome Ruby documentation browser!' },
- { :title => 'The egalitarian assumption of the modern citizen' },
- { :title => '', :_destroy => '1' } # 该记录会被忽略
- ]
- }
- }
- member = Member.create(params['member'])
- member.posts.length # => 2
- member.posts.first.title # => 'Kari, the awesome Ruby documentation browser!'
- member.posts.second.title # => 'The egalitarian assumption of the modern citizen'
:reject_if 也可一接受一个symbol来代表一个可用方法:如果hash中含有一个id和已有的关联记录相匹配,则被匹配到的记录会被修改:Ruby代码
- class Member < ActiveRecord::Base
- has_many :posts
- accepts_nested_attributes_for :posts, :reject_if => proc { |attributes| attributes['title'].blank? }
- end
- params = { :member => {
- :name => 'joe', :posts_attributes => [
- { :title => 'Kari, the awesome Ruby documentation browser!' },
- { :title => 'The egalitarian assumption of the modern citizen' },
- { :title => '' } # 这个记录会被忽略
- ]
- }}
- member = Member.create(params['member'])
- member.posts.length # => 2
- member.posts.first.title # => 'Kari, the awesome Ruby documentation browser!'
- member.posts.second.title # => 'The egalitarian assumption of the modern citizen'
默认关联记录是被保护的(不被删除)。如果想通过属性hash来删除任何关联记录,你需要打开:allow_destroy选项, 这样使用_destroy键来删除记录就行:Ruby代码
- member.attributes = {
- :name => 'Joe',
- :posts_attributes => [
- { :id => 1, :title => '[UPDATED] An, as of yet, undisclosed awesome Ruby documentation browser!' },
- { :id => 2, :title => '[UPDATED] other post' }
- ]
- }
- member.posts.first.title # => '[UPDATED] An, as of yet, undisclosed awesome Ruby documentation browser!'
- member.posts.second.title # => '[UPDATED] other post'
Ruby代码
- class Member < ActiveRecord::Base
- has_many :posts
- accepts_nested_attributes_for :posts, :allow_destroy => true
- end
- params = { :member => {
- :posts_attributes => [{ :id => '2', :_destroy => '1' }]
- }}
- member.attributes = params['member']
- member.posts.detect { |p| p.id == 2 }.marked_for_destruction? # => true 标记将被删除
- member.posts.length # => 2 未保存,所以还没删除
- member.save
- member.reload.posts.length # => 1
保存
所有对model修改的行为,包括标记将要销毁,会随着parent被保存原子性的被自动保存或者删除。这些开始与parent的save方法,发生在其内部的事务里。详见 Active Record Autosave Association
使用attr_accessible
使用attr_accessible如果不小心,可能会干扰到嵌套属性的使用。例如,上述member model如下使用attr_accessible:你需要这样的修改:Ruby代码
- attr_accessible :name
Ruby代码
- attr_accessible :name, :posts_attributes
验证parent model 的存在
如果你想验证一个child记录是否和一个parent记录关联,你可以使用validates_presence_of和inverse_of:
Ruby代码 - <span style="font-size: xx-small;">class Member < ActiveRecord::Base
- has_many :posts, :inverse_of => :member
- accepts_nested_attributes_for :posts
- end
-
- class Post < ActiveRecord::Base
- belongs_to :member, :inverse_of => :posts
- validates_presence_of :member
- end</span>
具体应用见 http://cn.asciicasts.com/episodes/196-nested-model-form-part-1
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