ruby-on-rails-3 - 导轨 : Belongs_to Polymorphic Association + conditions

Question

所以我有这个模型:

class Model < ActiveRecord::Base
  attr_accessible :to_id, :to_type

  belongs_to :to, polymorphic: true

end

我想知道当belongs_to 处于特定类型时是否可以添加另一个关系:

class Model < ActiveRecord::Base
  attr_accessible :to_id, :to_type

  belongs_to :to, polymorphic: true
  belongs_to :to_user, :foreign_key => :to_id, :conditions => ['to_type = ?', 'User'] # doesn't work
  # OR MAYBE
  belongs_to :to_user, :foreign_key => :to_id, :foreign_class => 'User' # It doesn't check on Model's to_type...
end

所以 my_model.to_user将返回 user如果存在，和 nil如果未设置或属于不同类别。

使用 Rails 3.2

谢谢!

Answer 1

你可以在里面使用 where 条件，比如

 belongs_to :to_user,-> {where(:to_type=> 'User')},  :foreign_key => :to_id

表格更多看看这个 association callbacks