Rails JBuilder recursive lookup - ruby-on-rails

Question

I am using Rails 4, and I have some simple models as follow:
class Question < ActiveRecord::Base
# columns (id, text)
has_many :answers
end
class Answer < ActiveRecord::Base
# columns (id, text, next_question_id)
belongs_to :question
end
You can see that an answer has a next_question_id column, which will be used to look up another question. I want to generate a tree-structure json like this:
{
"text": "This is question 1",
"answers": [
{
"text": "This is answer a",
"next_question": {
"text": "This is question 2",
"answers": [
{
"text": "This is answer c",
"next_question":
}
]
}
},
{
"text": "This is answer b",
"next_question": {
"text": "This is question 2",
"answers": [
{
"text": "This is answer d",
"next_question":
}
]
}
}
]
}
How can I achieve this with JBuilder? I tried the solution here, but I cannot pass the json argument to the helper function.

Answer 1

The standard aproach for rendering trees is using a recursive partial. To implement this you'll first need to add a method to your Answer model like this.
def next_question
Question.find(next_question_id) if next_question_id
end
(hint: alternetively you could just set a belongs_to :next_question, class_name: Question association on your Answer model)
Then you create a partial like _question.json.jbuilder that goes like this:
json.(question,:id, :text)
json.answers question.answers do |answer|
json.(answer, :id, :text)
json.partial!(:question, question: answer.next_question) if answer.next_question
end
Then in the controller you take the first question in your survey and put it in say the #first_question variable.
And the last thing: in your view you write
json.partial! :question, question: #first_question