Chapter 1
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In fact, for more complex problem domains that have a small and exible
Controller handling the actual business logic via models usually gives the
most maintainable results.
A Model is a source of data. Most applications use a single relational database such
as MySQL or PostgreSQL as their Model, but Catalyst does not require that—you can
use anything from les on a disk, to an e-mail server, or remote RSS feeds; also you
can have as many Models as your application needs.
Each Model knows how to congure itself at startup (for example, connect to the
database server), so you'll never have to worry about that. If you need to use a
different database, you can change the connection information in one le, restart your
application, and the change will take effect everywhere, automatically. The repetition
that a traditional application would require is simply non-existent in Catalyst.
Lastly, a View is another component that your action may use. Only a very limited
subset of applications will not need at least one View component.
A View is a way to turn the raw data that your action generates into something more
useful to your application's users. Typically, applications have a View that converts
the data into an HTML page via a templating system, such as the Template Toolkit,
Mason, or ClearSilver.
The View is generally responsible for all matters of representing the response. This
also includes serializations such as JSON, or RSS, and Atom feeds.
Templating systems abstract your HTML or XML away from your Perl code, so the
web designer can edit it without knowing anything about Perl or the underlying
design of your application.
You don't have to completely understand what MVC is right now—we'll start
learning the details in the next chapter. For now, think about all the code you've
cut and pasted between les in your application and how Catalyst will eliminate
that forever.
Extensibility
MVC isn't all that Catalyst provides. At the time of writing, there were over 190
freely available plugins that added new features to Catalyst. Existing plugins
offer functionality such as conguration le parsers, specialized logging tools,
e-mail interfaces, caching, user authentication and authorization, cryptography,
internationalization and localization, browser detection, and even virus scanning.
Most of these plugins drop right into your application and instantly provide you
with the advertised functionality. This saves you from having to reinvent the wheel
for common (and uncommon) tasks.
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