We all know, Comments are every where Blogs, Social Networking sites, e-learning forums etc. In this article, we've got an Article model and we want to create a nested commenting system onto that. Such that Article can have comments, comments can have replys, replys can have more replys and so on. For example - This is an article This is an comment this is a reply this is a reply's reply .... (so on) This is another comment. Now, we're going to talk about polymorphic associations and what they are and how they can be implemented for nested commenting system. What