I have a blog where users can post comments. When creating a comment, various things happen: creating the comment object, associations, persisting sending notification emails to post's author given his preferences sending notification to moderators given their preferences updating a fulltext database for search ... I could put all this in the controller, but what if I want to reuse this code ? e.g. I would like to provide an API for posting comments. I could also put this in the model, but I wonder if I won't lose flexibility by doing so. And would it be acceptable to do all of this from the model layer ? What would you do ?