Where to load data for things like a sidebar in MVC frameworks?

Question

This seems extremely basic, but I've read a lot of related questions and haven't found a proper answer.

Using Ruby on Rails or other similar MVC framework, how am I supposed to load data that is displayed in sidebars on multiple pages?

Options I know of, with the problems I see:

• Load it in every controller method that needs it: causes duplication of code;
• Load it in a method on the ApplicationController, which is executed by all controllers: would cause data to be loaded even when not needed;
• Load it directly from the model in the view: not MVC?

I've asked this elsewhere and some people told me to "look into [insert another pattern here]" or "use Ajax calls to get the data". Although those might also work, I'm looking for an answer regarding MVC frameworks on the server.

Answer 1

Typically, I think the duplication is best handled by pushing the shared code up into a superclass (either in ApplicationController or some other superclass your controller inherits from) as a private method. I think nowadays DHH wants you to put your shared code in modules (erm, i mean concerns), and include those in your controllers, as opposed to shoving everything in ApplicationController.

Depending on your situation you'd either run the code in a before_filter on each controller action where you have your sidebar, or put the before_filter up in a superclass and call skip_before_filter when you dont want the code run before a specific controller action.

Also, its certainly possible to use ajax to accomplish this but unless you have a really good reason, I would avoid doing it that way.

There are also times when I think calling class methods on a model directly from a view is perfectly OK. Like getting simple counts, for example.

Answer 2

You may be having trouble if you are thinking of all MVC as a 1 to 1 relationship of View to Controller and a View per Page. A view is not necessarily a page and a page is not necessarily a single view. Commonly they are 1 to 1, but often there is more to it. You might have pages made up of a handful of views, though there will usually be one master view that correlates to the current controller.

Rather than make it part of multiple controllers, you can dedicate a new controller to the sidebar and call it SideBarController. It has its own view.

In ASP.NET MVC land, I'd call it a partial view. Basically a fragment of markup that is included in a master page or set of pages. A master page is often a template page with header, footer, left nav, and main content. In RoR land, I think its done using explicit render

Example, my ProductsController returns a view, the Products index page renders, and inside that template page there is a markup tag that calls SideBar.

Not touched Rails in years, but I think:

render template: "sidebar/show"

Or simply:

render "sidebar/show"

Is enough since it Rails knows its a different controller with the embedded slash.

http://guides.rubyonrails.org/layouts_and_rendering.html