can't get mongoid/rails field to accept input as array - ruby-on-rails

Question

I'm creating a Question/Answer model in a Mongoid/Rails project. I want users to create their own questions and then create possible answers: 2 answers or 3 answers or more. I've got the form so they can add as many questions as they want, but I get this error:
Field was defined as a(n) Array, but received a String with the value "d".
Not only am I not getting the array, but it's wiping out "a" "b" and "c" answers and only saving "d".
My model:
class Question
include Mongoid::Document
field :question
field :answer, :type => Array
end
The relevant section of _form.html.haml:
.field
= f.label :question
= f.text_field :question
%p Click the plus sign to add answers.
.field
= f.label :answer
= f.text_field :answer
#plusanswer
= image_tag("plusWhite.png", :alt => "plus sign")
.actions
= f.submit 'Save'
The jQuery that repeats the answer field when they need it:
$("#plusanswer").prev().clone().insertBefore("#plusanswer");
I've tried several of the solutions here involving [] in the field but getting nowhere.
Thanks much.

Answer 1

Two approaches:
One is to edit the form such that instead of returning back question[answer], it returns question[answer][] which will build answer to be an array.
EDIT: I'm reading your question closer and it seems like you have some JS dynamically rendering forms. In that case, setting the id with an empty bracket set [] at the end should turn the form object returned into an array
The other is to override the setter in the model to convert a string into an array. The safest way is to create a matching getter
class Question
field :answer, type: Array
def answer_as_string
answer.join(',')
end
def answer_as_string=(string)
update_attributes(answer: string.split(','))
end
end
Then use :answer_as_string in your form

Answer 2

If you don't want to do a lot wrangling back and forth of the values between javascript and your model and you understand how to use fields_for and nested attributes a better approach might be to make answers separate model and embed them in the question model as so:
class Question
include Mongoid::Document
embeds_many :answers
end
class Answer
include Mongoid::Document
field :content # or whatever you want to name it
end
Your form would look like this (pardon my HAML):
.field
= f.label :question
= f.text_field :question
%p Click the plus sign to add answers.
= f.fields_for :answers do |ff|
.field
= ff.label :content
= f.text_field :content
#plusanswer
= image_tag("plusWhite.png", :alt => "plus sign")
.actions
= f.submit 'Save'