Rails%203%20In%20Action

Brand-new engine
engine.rb. This folder works in the same way that it does in an application, providing a
home for the images, JavaScript files, and stylesheets that are served by the sprockets
gem. Providing that either the host application or the engine 13 specifies a dependency
on CoffeeScript or Sass, you can use these as well.
Inside the app directory lies the app/controllers directory, which serves the same
purpose as the app/controllers directory in a Rails application. This directory has a
key difference though: the controllers should be placed into a forem namespace so
that they do not clash with identically named controllers in the application. If you
moved these controllers out of the namespace, they’d clash with controllers of the
same name in the application, or in other engines that aren’t using namespacing. By
namespacing them, you prevent this error from happening. This also explains why the
helpers in app/helpers are also separate.
Your Forem::ApplicationController currently inherits from ActionController
::Base, but in the case of your engine you’ll want it to inherit from Application-
Controller instead. Therefore, you’ll change app/controllers/forem/application
_controller.rb from this
module Forem
class ApplicationController
into this:
module Forem
class ApplicationController
You must use the :: prefix on the super ApplicationController so that it goes to the
top-level ApplicationController, not the one inside the Forem model that you’re
defining! By inheriting from the ApplicationController, your engine will use the
same layout as the application it’s hosted within.
Within the app directory, you can define models which also go under a
namespace. If you had a Forum model, it would live at app/models/forem/forum.rb
and would be called Forem::Forum. By doing this, you separate the model class from
any identically named class in the application or other engines. The default table
name for this model would be forums if it weren’t for some additional configuration
in lib/forem/engine.rb that you’ll see later.
With models also come migrations. When you create migrations in an engine,
these are stored (again, like an application) in db/migrate. When you (or others)
install the engine into an application, there’s a rake forem:install:migrations task
that will copy across these migrations, adding the migrations to the current list of
migrations in the application’s db/migrate folder. If a new version of the engine is
released, the user can re-run rake forem:install:migrations and it will only copy
across the newer migrations.
13 It’s best to specify this dependency in the engine if you wish to use either of these.
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