Is there a rails helper for this case?
You have a Survey, which has_many Questions, which has_many Answers.
s = Survey.first
s.answers # => Returns the answers of all the survey questions
I didn't want to recreate the wheel here.
It's built in:
class Survey < ActiveRecord::Base
has_many :questions
has_many :answers, :through => :questions
# ...
end
That's it. Now you can call survey.answers and it'll get all the answers.
Read up on the :through option (and its limitations) here
Related
This feels like it should be super simple, but for the life of me I haven't been able to get it right.
In my application, I want to have Questions and Answers.
A Question can only have 1 Answer, but an Answer can be used for many Questions.
For example.
Question Table Data
"Two plus Two equals?"
"Number of sides to a square?"
Answer Table Data
Four
Both Questions only have 1 Answer, but the Answer record can be used for both Questions.
I thought maybe this would work ::
rails g resource question verbiage:string answer:references
but then I have to put a belongs_to :answer on the Question model and that doesn't seem right.
It feels like it should be possible to do something like ::
Question.first.answer # returns the single answer
Answer.first.questions # returns all of the Questions where this record is the Answer
Can anyone educate me on the proper way to model this in ActiveRecord?
You need has_many assosiaction.
I'm gonna use scaffold for this.
Create Answer:
rails g scaffold Answer value:string
Create Question:
rails g scaffold Question verbiage:string answer:references
Run rails db:migrate
Create assosiactions.
class Answer < ApplicationRecord
has_many :questions
end
class Question < ApplicationRecord
belongs_to :answer
end
If you don't want to use demir's answer of
question belongs_to answer
answer has_many question
You'll have to
Make a QuestionAnswer join table
QuestionAnswer belongs_to question
QuestionAnswer belongs_to answer
question has_one question_answers
answer has_many question_answers
Then
question has_one :answer through :question_answer source :answer
answer has_many :question through :question_answer source :question
Ex. https://guides.rubyonrails.org/association_basics.html#choosing-between-belongs-to-and-has-one
For example, it makes more sense to say that a supplier owns an account than that an account owns a supplier. This suggests that the correct relationships are like this
This really depends on what the requirements are. In most cases you actually need a join table:
class Question
has_many :options
has_many :answers, through: :options
end
class Option
belongs_to :question
belongs_to :answer
end
class Answer
has_many :options
has_many :questions, through: :options
end
answers = [Answer.create(verbiage: 'Dailey'), Answer.create(verbiage: 'Once a week'), Answer.create(verbiage: 'Never')]
question = Question.create(verbiage: 'How often do you drink milk?', answers: answers)
question_2 = Question.create(verbiage: 'How often do you excercise?', answers: answers)
If the question is has a correct answer you can use a separate association which is a direct link to the the answers table:
class Question
has_many :options
has_many :answers, through: :options
belongs_to :correct_answer, class_name: 'Answer'
end
Or you can add a boolean column to the options table if their can be multiple correct answers.
class Question
has_many :options
has_many :answers, through: :options
has_many :correct_answers, through: :options,
class_name: 'Answer',
-> { where(options: { correct: true }) }
end
I have 3 models: Quiz, which has_many questions, which has_many answers. The lower models all belongs_to the model intuitively above them (quiz > questions > answers).
My problem is that I want to get a collection of all the answers. I thought I could do this with something like quiz.questions.answers or quiz.questions.all.answers but I just get an error undefined method 'answers'. Why is this happening and how do I fix it?
Answer belongs to one Question so you cannot call answers on a collection of questions, so if you want all the answers of all the questions of a quiz then you can do something like this to achieve, in Quiz model add this
has_many :answers, through: :questions
By adding that you will be able to fetch all the answers directly by doing quiz.answers.
Now, if you want to get answers of specific questions then you can do something like this
quiz = Quiz.where(id: quiz_id).include(:questions => :answers)
quiz.questions.each do |question|
answers = question.answers
# perform some action
end
Hope that helps!
This is the perfect example of something that needs a "through" association.
class Quiz
has_many :questions
has_many :answers, :through => :questions
Then:
my_quiz.answers
class Quiz < ActiveRecord::Base
has_many :questions
has_many :answers, through: :questions
end
class Question < ActiveRecord::Base
belongs_to :quiz
has_many :answers
end
class Answer < ActiveRecord::Base
belongs_to :question
end
Then you can have,
quiz = Quiz.last
quiz.questions
quiz.answers
Say I have two models, Question which has_many Answers and Answers which belongs_to question. If in my Users model I add has_many Questions, would Users then automatically has_many Answers as well, or would I need to add has_many Answers manually?
You should read up on the "has many through" relationship.
http://guides.rubyonrails.org/association_basics.html#the-has-many-through-association
Not automatically. For users to have many answers, you'd want to use :through, e.g.,
class User < ActiveRecord::Base
has_many :questions
has_many :answers, through: :questions
end
See: http://guides.rubyonrails.org/association_basics.html#the-has-many-through-association
If you have the following setup:
class User << ActiveRecord::Base
has_many :questions
end
class Question << ActiveRecord::Base
has_many :answers
end
class Answer << ActiveRecord::Base
belongs_to :question
end
You can't get to all user's answers with a single method. You would have to get all questions as a collection and then iterate through your questions collection and get all the answers. This would obviously lead to N+1 query problem.
#user.questions.map(&:answers).flatten
To solve that N+1 query problem, you'd have to use .includes(), but again that would only solve the N+1 problem.
#user.questions.includes(:answers)
Solution: use has_many :through
If you add has_many :through into your User model:
class User << ActiveRecord::Base
has_many :questions
has_many :answers, through: :questions
end
This would allow you to access your user's answers with a single method like this:
#user.answers
I have an AnswerSheet that has_many :answers, and each Answer belongs_to :question.
I do something like #answer_sheet.answers.where(is_correct: false).map(&:question) to get all the incorrectly answered questions.
Question has_many :question_skills and has_many :skills, through: :question_skills, and I want to get all the unique skills for that set of questions.
I had tried .map(&:skills) on the result of the above, but that gives me an array of ActiveRecord::Associations::CollectionProxy, which I think is not quite what I want.
This also seems like a performance nightmare.
If you have suggestions on how to improve this question title, I'd be more than happy to generalize the question.
You can use associations to answer all these questions (pun intended). First, add some new associations for correct/incorrect answers.
class Answer < ActiveRecord::Base
belongs_to :question
end
class AnswerSheet < ActiveRecord::Base
has_many :answers
has_many :incorrect_answers, -> { where is_correct: false }, class_name: 'Answer'
has_many :incorrectly_answered_questions, class_name: 'Question', through: :incorrect_answers, source: :question
has_many :correct_answers, -> { where is_correct: true }, class_name: 'Answer'
has_many :correctly_answered_questions, class_name: 'Question', through: :correct_answers, source: :question
has_many :skills_for_correct_answers, class_name: 'Skill', through: :correctly_answered_questions, source: :skills
has_many :skills_for_incorrect_answers, class_name: 'Skill', through: :incorrectly_answered_questions, source: :skills
end
Now you can get at the records more directly:
# get all incorrect answers
answer_sheet.incorrect_answers
# get all incorrectly answered questions
answer_sheet.incorrectly_answered_questions
# get all correctly answered questions
answer_sheet.correctly_answered_questions
Your second question about how to find the unique skills can be done by calling uniq on the results
answer_sheet.skills_for_incorrect_answers.uniq
It's normally best to let the DB formulate the answer from a single query. For the first query, this would be something like:
Question.joins(:answer_sheets, :answers).where(
'answer_sheets.id = ? and not answers.is_correct', #answer_sheet.id)
and with this as a pattern, for the second:
Skill.joins(:questions, :answer_sheets, :answers).select('skills.id,skills.text').
where('answer_sheets.id = ? and not answers.is_correct', #answer_sheet.id).
distinct
We need the select to allow distinct to work. Adjust fields as needed.
Of course this is untested, but it ought to be close.
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I have the following models:
user.rb
has_many :places
has_many :orders
has_one :cart
has_many :order_transactions
product.rb
class Product
has_many :purchases
has_many :line_items
has_many :orders, :through => :order_products
lineitem.rb
class LineItem
belongs_to :product
belongs_to :cart
belongs_to: order
order.rb
class Order
belongs_to :user
belongs_to :product
has_many :purchases
has_many :line_items, :dependent => :destroy
has_many :orders, :through => :order_products
Hi guys, I face a problem in retrieving the user who list up the product. As the site I am currently working on allows users to list up products for sale, how am i suppose to credit the earnings to the respective user? I understand that I would have to first retrieve the user who list up the product.
However, I am unable to do so from order controller based on the association I have now.
Appreciate any help out there. Thanks.
You have not specified the relationship between users and products in your models.
User.rb - add:
has_many :products
Product.rb -aa:
belongs_to :user
You will also need to be sure the user_id is in the product table, and the product_id is in the user table.