ruby-on-rails - accepts_nested_attributes_for 未定义方法错误

Question

我正在尝试使用 accepts_nested_attributes 来创建一个复杂的表单。基于Nested Attributes文档，examples等，我已经像这样设置了模型:

用户模型:

require 'digest'
class User < ActiveRecord::Base
  attr_accessor :password
  attr_accessible :first_name, :last_name, :email, :password, 
                  :password_confirmation, :ducks_attributes

  has_many :ducks, :class_name => 'Duck'
  accepts_nested_attributes_for :ducks
  .
  .
  .
end

鸭模型:

class Duck < ActiveRecord::Base
  belongs_to :user
  accepts_nested_attributes_for :user
end

但是当我尝试访问控制台中的嵌套属性时，我得到了

ruby-1.9.2-p290 :003 > User.first.ducks_attributes
NoMethodError: undefined method `ducks_attributes' for #<User:0x007ffc63e996e0>
    from ~/.rvm/gems/ruby-1.9.2-p290@rails3tutorial/gems/activemodel-3.0.9/lib/active_model/attribute_methods.rb:392:in `method_missing'
    from ~/.rvm/gems/ruby-1.9.2-p290@rails3tutorial/gems/activerecord-3.0.9/lib/active_record/attribute_methods.rb:46:in `method_missing'
    from (irb):3
    from ~/.rvm/gems/ruby-1.9.2-p290@rails3tutorial/gems/railties-3.0.9/lib/rails/commands/console.rb:44:in `start'
    from ~/.rvm/gems/ruby-1.9.2-p290@rails3tutorial/gems/railties-3.0.9/lib/rails/commands/console.rb:8:in `start'
    from ~/.rvm/gems/ruby-1.9.2-p290@rails3tutorial/gems/railties-3.0.9/lib/rails/commands.rb:23:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

我做错了什么？非常感谢。

Answer 1

只定义了属性writer。

class User < ActiveRecord::Base
  has_many :ducks
  accepts_nested_attributes_for :ducks
end

class Duck < ActiveRecord::Base
  belongs_to :user
end

# This works:
User.first.ducks_attributes = [ { :name => "Donald" } ]

# This is more common (attributes posted from a form):
User.create :ducks_attributes => [ { :name => "Donald" }, { :name => "Dewey" } ]