| These are my assumptions: 1.The performance goal is to return http & html headers as quickly as possible. 2. Business logic belongs in the models, as triggered by method invocations from the controller. 3. A good deal of time is spent on business logic and request handling (authentication / set-up / before_filter stuff.) Often, this requires network I/O to backend systems (or databases.) While some data retrieval is necessary only to render the view (and can thus be deferred gracefully,) other times your application logic depends the completion of these lengthy requests in order to complete the desired state modification. 4. Since we want to return the headers as quickly as possible, we can either a) figure out how to send the headers before the controller or b) figure out how to delay the processing until after the controller. --- I think that that a) is better than b). I like views that exclusively take data and format it for output. I like having the core business logic in the models, and I like having the system guards and request setup concentrated in the controllers. This way, I can have an exhaustive understanding of the tasks performed by an action without having to read through all of the views and their partials. If we hide some of the processing within model actions and call those model actions from the view, then I no longer can assume that all major processing / I/O has happened by simply reading the controller and the model methods it invokes. Instead, I also have to read all of the views. This violates the expectations I have about processing times and MVC. If instead, we could detect the requested format and return immediately with the headers, then we could perform the overwhelming majority of the processing while the browser is busy downloading static assets. |
However I see the core team's point that they don't want to completely overhaul the API in a way that's going to break arguably a majority of existing apps, and at the same require the developer to pay attention to more details than may be necessary.
However on the topic of breaking expectations about processing times, I couldn't disagree more. To me, the main benefit of MVC (or any architecture choice) is in isolating responsibilities, not isolating code execution. It's not a big mental leap to conceive of a ActiveRecord relation as declaring some data that's needed that may or may not be actually queried, depending on if the view needs it. This helps your MVC separation, because it means you don't need to extract view logic from your template just to make sure the controller doesn't load something unnecessarily. Lazy execution of this form is a very powerful optimization technique, just ask any Haskeller.