一个member有一些post

class Member < ActiveRecord::Base

has_many :posts

accepts_nested_attributes_for :posts

end

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 => true

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'

通过 :reject_if proc设置忽略的不满足条件的记录。例如：

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'

: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：

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'

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:

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