Rails - 如何设置可以属于3种不同模型的模型 [英] Rails -- How to setup model that can belong to either of 3 different models

问题描述

我试图创建一个类似于在学校体验的测试应用程序。

I'm trying to make an app that does testing similiar to what you would experience in school.

我有一个模型问题，可以属于考试，测验或作业。

I have a model Question, which can belong to either an Exam, Quiz, or Assignment.

我应该为：exam_id，：integer，：null => false;：quiz_id，：integer，：null => false;：assignment_id，：integer ，：null => false;？

Should I create fields for ":exam_id, :integer, :null => false; :quiz_id, :integer, :null => false; :assignment_id, :integer, :null => false;"?

问题将属于其中一个或几个或全部（因此我可以在diff模型中重用相同的问题） 。

The question will belong to either one or a few or all of them ( so i can reuse the same question in diff models).

我应该删除：null => false，所以它可以属于他们....或者什么是最好的方式来设置它？ >

Should I remove the :null=>false so it could belong to either of them....or what the best way to set that up?

推荐答案

这听起来像你想做的是使用多态关系。您将需要一个通用名称进行考试/测验/作业，每个问题将属于其中之一。假设您称为评估，您将按如下方式设置您的模型：

It sounds like what you want to do here is use a polymorphic relationship. You will need a generic name for exam/quiz/assignment and each question will belong to one of these. Say you call them Assessments, you would set up your models like this:

class Question << ActiveRecord::Base
  belongs_to :assessment, :polymorphic => true
end

class Exam << ActiveRecord::Base
  has_many :questions, :as => :assessment
end

class Quiz << ActiveRecord::Base
  has_many :questions, :as => :assessment
end

class Assignment << ActiveRecord::Base
  has_many :questions, :as => :assessment
end

然后，您需要向您的Question模型中添加两​​个字段： / p>

Then you will need to add two fields to your Question model:

assessment_id
assessment_type

有了这种关系，你可以使用它：

With this relationship, you can use it like:

@exam = Exam.create({:field1 => :val1})    
@exam.questions.create({:field1 => :question1})
@exam.questions.create({:field1 => :question2})

，它会根据问题模型中的附加字段确切地知道哪些问题属于哪个模型。

and it will know exactly which questions belong to which model based on the additional fields in your question model.

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