In this post to his site Marko Pavlovic talks about REST APIs, some of the non-CRUD (create, read, update, delete) operations that need to be performed and how the Command design pattern can help.

We’ve all been here: the data model has been designed, and we have the entities and relationships implemented. It is finally time to code up the business logic and we are faced with solving these problems: The actions we want to implement on a particular model are not part of the good old CRUD (Create, Read, Update, Delete) operations, and we need to make a lot of non-standard controller actions, and routes. [Also] the actions we want to implement do not belong to a any model, and we have to create a new controller just for the "API".

He gives a more concrete example to illustrate the problem using "sites", "visits" and a desire to add analytics functionality using each's data. He points out two common actions taken when something like this comes up: either new methods on the pre-existing controllers or possibly making a new controller to handle it. Instead he suggests using the Command pattern to handle requests themselves as self-contained items. This gathers all the logic needed in to one place and the Report instance can then be used as-is by the response that needs to render the results.