Ruby-on-rails 在 Rails 中找不到关联问题

Could not find the association problem in Rails

提问by Ash

I am fairly new to Ruby on Rails, and I clearly have an active record association problem, but I can't solve it on my own.

我是 Ruby on Rails 的新手，我显然有一个活动记录关联问题，但我无法自己解决。

Given the three model classes with their associations:

给定三个模型类及其关联：

# application_form.rb
class ApplicationForm < ActiveRecord::Base
  has_many :questions, :through => :form_questions
end

# question.rb
class Question < ActiveRecord::Base
  belongs_to :section
  has_many :application_forms, :through => :form_questions
end

# form_question.rb
class FormQuestion < ActiveRecord::Base
  belongs_to :question
  belongs_to :application_form
  belongs_to :question_type
  has_many :answers, :through => :form_question_answers
end

But when I execute the controller to add questions to application forms, I get the error:

但是当我执行控制器向申请表添加问题时，出现错误：

ActiveRecord::HasManyThroughAssociationNotFoundError in Application_forms#show

Showing app/views/application_forms/show.html.erb where line #9 raised:

Could not find the association :form_questions in model ApplicationForm

Can anyone point out what I am doing wrong?

谁能指出我做错了什么？

回答by Jim

In the ApplicationForm class, you need to specify ApplicationForms's relationship to 'form_questions'. It doesn't know about it yet. Anywhere you use the :through, you need to tell it where to find that record first. Same problem with your other classes.

在ApplicationForm 类中，您需要指定ApplicationForms 与'form_questions' 的关系。它还不知道。:through无论在何处使用，都需要先告诉它在哪里可以找到该记录。你的其他班级也有同样的问题。

So

所以

# application_form.rb
class ApplicationForm < ActiveRecord::Base
  has_many :form_questions
  has_many :questions, :through => :form_questions
end

# question.rb
class Question < ActiveRecord::Base
  belongs_to :section
  has_many :form_questions
  has_many :application_forms, :through => :form_questions
end

# form_question.rb
class FormQuestion < ActiveRecord::Base
  belongs_to :question
  belongs_to :application_form
  belongs_to :question_type
  has_many :form_questions_answers
  has_many :answers, :through => :form_question_answers
end

That is assuming that's how you have it set up.

那是假设这就是您设置的方式。

回答by bensie

You need to include a

你需要包括一个

has_many :form_question_answers

In your FormQuestion model. The :through expects a table that's already been declared in the model.

在您的 FormQuestion 模型中。:through 需要一个已经在模型中声明的表。

Same goes for your other models -- you can't supply a has_many :throughassociation until you've first declared the has_many

您的其他模型也是如此——has_many :through在您首先声明has_many

# application_form.rb
class ApplicationForm < ActiveRecord::Base
  has_many :form_questions
  has_many :questions, :through => :form_questions
end

# question.rb
class Question < ActiveRecord::Base
  belongs_to :section
  has_many :form_questions
  has_many :application_forms, :through => :form_questions
end

# form_question.rb
class FormQuestion < ActiveRecord::Base
  belongs_to :question
  belongs_to :application_form
  belongs_to :question_type
  has_many :form_question_answers
  has_many :answers, :through => :form_question_answers
end

It looks like your schema might be a bit wonky, but the point is you always need to add the has_many for the join table first, then add the through.

看起来您的架构可能有点不稳定，但关键是您始终需要先为连接表添加 has_many，然后添加通过。