Rails%203%20In%20Action

476 CHAPTER 17 Engines
This file’s second line of real code here requires the test/dummy/config/environment
.rb file, which loads the application in test/dummy.
TEST/DUMMY
The application contained within this directory is purely for testing purposes, but you
can set it up to act like a real application by creating controllers, helpers, models,
views, and routes if you wish. When the tests run, this application is initialized like a
real Rails application.
Your tests then run against this application, which has your engine mounted inside
the test/dummy/config/routes.rb file with this line:
mount Forem::Engine => "/forem"
This line mounts the routes of your engine (not yet defined) at the /forem path of
your application. This means that whenever you want to access this engine, you must
prefix the route with /forem. If you are in code, you can use the forem. prefix for the
routing helpers, as seen earlier with forem.forums_path or forem.root_path within
the dummy application.
Even though there are a lot of files that are generated for engines—like there are
when you generate an application—they all play a crucial role in your engine. Without
this lovely scaffold, you’d have to create it all yourself, which would be no fun.
This routing may be a little confusing at first, but it’s quite simple. Let’s look into
how this process works, and then you’ll get into developing your first feature for this
engine.
17.3.3 Engine routing
In an application, you need to define routes to an
engine when you’re using it. You can do that with this
line in config/routes.rb:
mount Forem::Engine, :at => "/forem"
To understand how engines are routed, you must understand
the concept of middleware within a Rails application.
14 Middleware is the term used for code that sits
between the receiving server and the application; middleware
can do a number of things, such as serve static
assets and set flash messages. Rails 3 applications run on
Rack, which uses a stack-based architecture to accomplish
a request. A basic stack is shown in figure 17.2.
In this picture, a basic request cycle for a Rails application
is shown. A request comes from a client and hits
Rack first, which then goes through all of the middleware.
If a middleware returns a 404 (“Not Found”)
14 Additional information about middleware can be found in chapter 18.
Middleware #1
404
Middleware #1
404
Client
Rack
Application
Figure 17.2
A simple middleware stack
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