通过关联belongs_to [英] belongs_to through associations

问题描述

鉴于以下关联，我需要从 Choice 模型中引用 Choice 附加的 Question.我一直在尝试使用 belongs_to :question, through: :answer 来执行此操作.

Given the following associations, I need to reference the Question that a Choice is attached through from the Choice model. I have been attempting to use belongs_to :question, through: :answer to perform this action.

class User
  has_many :questions
  has_many :choices
end

class Question
  belongs_to :user
  has_many :answers
  has_one :choice, :through => :answer
end

class Answer
  belongs_to :question
end

class Choice
  belongs_to :user
  belongs_to :answer
  belongs_to :question, :through => :answer

  validates_uniqueness_of :answer_id, :scope => [ :question_id, :user_id ]
end

我要了

NameError 未初始化的常量 User::Choice

NameError uninitialized constant User::Choice

当我尝试做 current_user.choices

它工作正常，如果我不包括

It works fine, if I don't include the

belongs_to :question, :through => :answer

但我想使用它，因为我希望能够执行validates_uniqueness_of

But I want to use that because I want to be able to do the validates_uniqueness_of

我可能忽略了一些简单的事情.任何帮助将不胜感激.

I am probably overlooking something simple. Any help would be appreciated.

推荐答案

belongs_to 关联不能有 :through 选项.您最好在 Choice 上缓存 question_id 并向表添加唯一索引(特别是因为 validates_uniqueness_of 容易出现竞争条件).

A belongs_to association cannot have a :through option. You're better off caching the question_id on Choice and adding a unique index to the table (especially because validates_uniqueness_of is prone to race conditions).

如果您有疑虑，请向 Choice 添加自定义验证，以确认答案的 question_id 匹配，但听起来似乎永远不应给最终用户机会提交会造成这种不匹配的数据.

If you're paranoid, add a custom validation to Choice that confirms that the answer's question_id matches, but it sounds like the end user should never be given the opportunity to submit data that would create this kind of mismatch.

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