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
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
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'm building a math exercise app. I want to store questions that are separated into exercises and each exercise belongs to a different section. Also there are multiple sections for each grade (12 grades in total).
How do i track a user's answer (action)? For instance, when a user browses the app, decides to answer question 7 from exercise 'G1' in section 'G' of Grade 'Pre-K' and provides a correct answer i want to track that and in the future provide him with statistics about his performance.
Currently there isn't a connection between my User model to the questions and i wanted to hear from others as to what would be the most efficient way to tackle this (maybe the models right now are completely wrong)
This is the model diagram for now with has_many, belongs_to relationship (i'll add 'the_question':string and 'answer':string later on to the question model):
I think all that is missing is a Answer model, that is connected to the User.
Optionally, you can define the relations on the "parents" of Question too.
class Grade < ActiveRecord::Base
has_many :users, :through => :sections # optional. i.e. 'users that have answers in this grade'
end
class Section < ActiveRecord::Base
has_many :users, :through => :exercises # optional
end
class Exercise < ActiveRecord::Base
has_many :users, :through => :questions # optional
end
class Question < ActiveRecord::Base
has_many :answers
has_many :users, :through => :answers # optional
end
class Answer < ActiveRecord::Base
belongs_to :question
belongs_to :user
end
class User < ActiveRecord::Base
has_many :answers
end
Update: re-reading your description, I think CorrectAnswer would be better suitable than Answer.
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
Like on StackOverflow, there is a question and that question has many answers.
But only one of the answers is marked as accepted.
How to implement the same thing in Rails?
The models and tables I have are:
class Question < ActiveRecord::Base
has_many :answers
has_one :accepted_answer # how to get this to work?
end
#Table: questions(id,question_text)
class Answer < ActiveRecord::Base
belongs_to :question
end
#Table: answers(id, question_id)
UPDATE (#voldy, thanks! But that doesn't seem to work?)
I added belongs_to :accepted_answer, :class_name => 'Answer' in the Question model.
Then added a accepted_answer_id and ran this code:
#question = current_user.questions.find(3)
an_answer = Answer.find(1) #presuming this is the answer i want to accept
#question.accepted_answer = an_answer
#question.save!
But the accepted_answer_id field in questions table remains null?
I also tried with field name as answer_id, but the same result.
I think there are different approaches. One of them is to add answer_id to questions table:
class Question < ActiveRecord::Base
has_many :answers
belongs_to :accepted_answer, :class_name => "Answer",
:foreign_key => :answer_id
end
class Answer < ActiveRecord::Base
belongs_to :question
end
Somewhere in the view if question.accepted_answer == answer etc.