Controller logic and template logic, where do you draw the line with pagination?

Question

The whole point of an MVC framework is to separate design (templates) from logic (controllers). However, template languages often afford a limited degree of "design logic" to occur. This includes basic if statements, loops, filtering, etc.

I've created a Django template tag that can take any list or QuerySet and "pagify" it. It splits the list up into pages based on a specified page size then adds the pages into the Context. The usage is as follows:

{% pagify articles by 20 as pages %}

I can then call a separate include to iterate over the pages and produce a nice list of pages wherever I needed it.

This seemed like an optimal way to do it because it allowed me to page any list in the context; I didn't have to rely on the controller to return paged results. But a colleague argued that this seemed like too much logic for the template. I thought this still fell within the realm of design-based logic since the page would still function even without paging, and determining page size feels like a template responsibility.

My question, is this too much logic for the template? or is this a clean way to be handling this?

Answer 1

The view should not contain business logic or navigation logic. What you are describing is presentation functionality (carefully avoiding the l-word here), which can be placed in the view layer.

Answer 2

I agree with your colleague; the template should be fed paginated data rather than performing the pagination. The key question, I think, is whether determining page size is a template duty, and I don't think so; I'd say it should be handled at a higher level.

Answer 3

It's always been my understanding that the view isn't supposed to be devoid of logic. It's just supposed to be devoid of any controller logic. Paging just has to do with how the data is displayed which is exactly what the view logic is supposed to contain.

Answer 4

Put it this way; what if you were using your data model in another medium, say, not on the web but via some kind of console-based application or background task? Wouldn't it be nice to be able to get "pages" of data through a controller (or manager) rather than having to somehow rely on a template to do this work for you?

While I'd certainly agree that the "look" of the paged data should be handled by your template, the "act" of paging should be left up to a controller (Django view) or even through some kind of custom manager (models.Manager) method.

Answer 5

You may want to check out django-pagination, which provides a similar template tag.