Ruby on Rails: Navigation Between Comments

Question

I'm attempting to create a button on the show page that will allow users to navigate between different comments.

And for some reason, I keep getting either article :id or comment :id could not be found.

Any idea why that happens?

#comment.rb

def self.next(comment, key = :id)
  self.where("#{key} > ?", comment.send(key)).first
end


#comments_controller.rb
class CommentsController < ApplicationController

  before_action :find_article
  before_action :find_comment

  def next_comment 
    @next_comment = @scope.next(@comment)
  end

  def scope
    @scope = @article.comments
  end
end

#comments/show.html.haml
= link_to "Next Comment", comments_next_comment_path(@next_comment)

EDIT: The problem was in my routes, which has now been fixed. But now I get the following error:

undefined method "next" for nil:NilClass

EDIT 2:

Here's the log--and the URL goes to http://localhost:3000/articles/14/comments/56/next_comment

Now it doesn't raise any errors but simply displays a blank page instead of going to the next comment URL which is http://localhost:3000/articles/14/comments/70

 Parameters: {"article_id"=>"14", "id"=>"56"}
  Article Load (0.2ms)  SELECT  "articles".* FROM "articles" WHERE "articles"."id" = ? LIMIT 1  [["id", 14]]
  Comment Load (0.1ms)  SELECT  "comments".* FROM "comments" WHERE "comments"."id" = ? LIMIT 1  [["id", 56]]
  Rendered comments/next_comments.html.haml within layouts/application (0.2ms)

Answer 1

The @scope instance variable is undefined (and therefore nil ) prior to you using it. Just change it to the following and it should work

def next_comment
  @next_comment = scope.next(@comment)
end

def scope
  @scope ||= @article.comments
end