Adding comments to article in Rails 5 (deeply nested resources) - ruby-on-rails

Question

I have a Rails app that has three main models: Qn, Ans, and Comments. I've been doing okay with 1-level-deep nested resources, but these three resources are nested deeply (Comments is shallowly nested) and they are all displayed in one single view, which makes it very confusing.
In a url like: http://localhost:3000/questions/2, the user can see all #question.answers displayed using a loop. In each of those answers, the user can see the answer.comments displayed using a loop. Below each answer, the user can also submit a new comment.
But after attempting several times to implement a 1) loop displaying all comments and 2) form for new comment, I always get some error along the lines of:
undefined method `model_name' for {:url=>"/questions/4/answers/2/comments/new"}:Hash
So I tried to pass in params #commentable instead of the answer, or point to the specific controller and action and so on, but none of these methods worked. I am guessing that I have an issue with my controllers to begin with, but I cannot seem to figure out what.
routes.rb (top ommited)
# Resources
resources :sessions
resources :users
resources :bookmarks # to be implemented later
resources :questions do
resources :answers do
resources :comments, shallow: true
end
end
Question model
class Question < ApplicationRecord
has_many :answers
has_many :bookmarks #later
end
Answer model:
class Answer < ApplicationRecord
belongs_to :question
has_many :comments, as: :commentable
has_many :likes, as: :likeable
validates :answercontent, length: {minimum: 50}
end
Comment model:
class Comment < ApplicationRecord
belongs_to :commentable, polymorphic: true
end
The show.html.erb (of QuestionsController)
<% #question.answers.each do |answer| %>
// ommited
<!-- Comments -->
<% answer.comments.each do |comment| %>
<%= comment.content %>
<br>
<% end %>
<!-- Submit new comment -->
<%= form_for(url: new_question_answer_comment_path, comment: {answer_id: answer.id, question_id: #question.id}) do |f| %>
<%= f.text_area :content %>
<%= f.submit "Submit" %>
<% end %>
<% end %>
QuestionsController (new, create, destroy ommited for brevity)
class QuestionsController < ApplicationController
def index
#questions = Question.all
end
def show
#question = Question.find(params[:id])
#answers = Answer.all
# Delete only appears when num_ans is 0
#deletable = (current_user== User.find(#question.user_id)) && (#question.answers.all.size==0)
end
private
def question_params
params.require(:question).permit(:picture_url, :country, :educational_level, :topic)
end
end
AnswersController (edit, update, destroy ommited for brevity)
class AnswersController < ApplicationController
def create
#question = Question.find(params[:question_id])
#answer = #question.answers.create(answer_params)
#answer.question_id = #question.id
#answer.user_id = current_user.id
if #answer.save
redirect_to #question
else
render :new
end
end
private
def answer_params
params.require(:answer).permit(:user_id, :question_id, :answercontent)
end
end
CommentsController
class CommentsController < ApplicationController
before_filter: load_commentable
def index
#commentable = Answer.find(params[:answer_id])
#comments = #commentable.comments
end
def new
#comment = #commentable.comments.new
end
def create
#comment = #commentable.comments.new(params[:comment])
if #comment.save
redirect_to #commentable
else
render :new
end
end
# From RailsCast ep.154
private
def load_commentable
resource, id = request.path.split('/')[1,2]
#commentable = resource.singularize.classify.constantize.find(id)
end
end
The routes
are quite messy right now so I will just post where the comments are:
question_answer_comments GET /questions/:question_id/answers/:answer_id/comments(.:format) comments#index
POST /questions/:question_id/answers/:answer_id/comments(.:format) comments#create
new_question_answer_comment GET /questions/:question_id/answers/:answer_id/comments/new(.:format) comments#new
edit_comment GET /comments/:id/edit(.:format) comments#edit
comment GET /comments/:id(.:format) comments#show
PATCH /comments/:id(.:format) comments#update
PUT /comments/:id(.:format) comments#update
DELETE /comments/:id(.:format) comments#destroy
Thanks in advance for the help.
Update:
To give you more info on what solutions I attempted:
1. Passing in two params like:
<%= form_for([answer, #comment], url: new_question_answer_comment_path(answer.id, #question.id)) do |f| %>
Gave me:
First argument in form cannot contain nil or be empty
Using #commentable (which is basically the answer) gives me an error saying that 'the id in #commentable.id doesn't exist as #commentable is nil'.
So I think the problem is that answer or #commentable is nil. But I specified it in the loop and in the controller too. So what else may I try?

Answer 1

form_for expects record as first argument, in your case it should be a comment instance. Also new_question_answer_comment_path expects values for question_id and answer_id keys, as you are creating a new comment, the route should be question_answer_comments not new_question_answer_comment so your form_for should be
<%= form_for Comment.new,url: question_answer_comments_path(#question,answer) do |f| %>
<%= f.text_area :content %>
<%= f.submit "Submit" %>
<% end %>
or just
<%= form_for [Comment.new,#question,answer] do |f| %>
<%= f.text_area :content %>
<%= f.submit "Submit" %>
<% end %>