Question

My group model has_many posts, posts have_many comments.

When I show the posts on a group, I want to order by the created at of the most recent comment, if there are any on a post, or by the created_at of the post itself.

So an old post would jump back to the top of the list if it has a new comment.

Answer 1

I would stick to a little different approach: your Comment belongs_to :post and belongs_to accepts :touch option. Set it to true and your Post’s updated_at will be automatically updated on a Comment’s modification. This way you can freely show your posts ordered by their updated_at.