Question

I’m trying to make a comment system, identical to the stackoverslow’s one. There’s a 1-st level comment, and a bunch of a second level comments, attached to it. The first straightforward idea that came up in order to do that, was to create a separate model, sub_comment. But I still got this feeling, that I should inherit the initial comment’s properties, only adding a simple comment-id joint.

I’m still a Rails newbie, so the question is – can I do that? How? Is it a simple

class sub_comment < comment 

model inheritance? But of course, I’m gonna need all the controller methods in order to add/delete these sub-comments. Or should I make a single comment model, where the 1-st level comment will have a nil as a parent?

What would be the right solution?

PS. Fell free to advice any book that covers the subject. I’m on a self education here, so I’d love to read everything that could clarify any future app architecture question.

Answer 1

I find it easier to have a simple tree structure with two pointers to make back-tracking easier:

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  acts_as_tree
  belongs_to :post

  named_scope :top_level, :conditions => { :parent_id => nil }
end

This makes it easy to retrieve all comments for a particular Post:

@comments = @post.comments.top_level

You can even pull up multiple levels of comments using AJAX or by fetching one layer after the next:

# Repeat while comments are found
loop do
  level = @post.comments.find(:all, :conditions => { :parent_id => @comments.collect(&:id) })

  if (level.empty?)
    break
  else
    @comments += level
  end
end

These can be sorted as required for presentation purposes.