Rails — How to setup model that can belong to either of 3 different models

Question

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

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

Answer 1

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

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

assessment_id
assessment_type

With this relationship, you can use it like:

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

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