3 Catalyst::Manual::Intro - Introduction to Catalyst
7 This is a brief overview of why and how to use Catalyst. It explains how
8 Catalyst works and shows how to get a simple application up and running quickly.
10 =head2 What is Catalyst?
12 Catalyst is an elegant web application framework, extremely flexible yet
13 extremely simple. It's similar to Ruby on Rails, Spring (Java) and L<Maypole>,
14 upon which it was originally based.
18 Catalyst follows the Model-View-Controller (MVC) design pattern, allowing you to
19 easily separate concerns, like content, presentation, and flow control, into
20 separate modules. This separation allows you to modify code that handles one
21 concern without affecting code that handles the others. Catalyst promotes the
22 re-use of existing Perl modules that already handle common web application
25 Here's how the M, V, and C map to those concerns, with examples of well-known
26 Perl modules you may want to use for each.
32 Access and modify content (data). L<Class::DBI>, L<Plucene>, L<Net::LDAP>...
36 Present content to the user. L<Template Toolkit|Template>, L<Mason|HTML::Mason>,
41 Control the whole request phase, check parameters, dispatch actions, flow
46 If you're unfamiliar with MVC and design patterns, you may want to check out the
47 original book on the subject, I<Design Patterns>, by Gamma, Helm, Johson and
48 Vlissides, also known as the Gang of Four (GoF). You can also just google it.
49 Many, many web application frameworks are based on MVC, including all those
54 Catalyst is much more flexible than many other frameworks. We'll talk more about
55 this later, but rest assured you can use your favorite Perl modules with
60 =item * B<Multiple Models, Views, and Controllers>
62 To build a Catalyst application, you handle each type of concern inside special
63 modules called L</Components>. Often this code will be very simple, just calling
64 out to Perl modules like those listed above under L</MVC>. Catalyst handles
65 these components in a very flexible way. Use as many Models, Views, and
66 Controllers as you like, using as many different Perl modules as you like, all
67 in the same application. Want to manipulate multiple databases, and retrieve
68 some data via LDAP? No problem. Want to present data from the same Model using
69 L<Template Toolkit|Template> and L<PDF::Template>? Easy.
71 =item * B<Reuseable Components>
73 Not only does Catalyst promote the re-use of already existing Perl modules, it
74 also allows you to re-use your Catalyst components in multiple Catalyst
77 =item * B<Unrestrained URL-to-Action Dispatching>
79 Catalyst allows you to dispatch any URLs to any application L<Actions>, even
80 through regular expressions! Unlike most other frameworks, it doesn't require
81 mod_rewrite or class and method names in URLs.
83 With Catalyst you register your actions and address them directly. For example:
86 my ( $self, $context ) = @_;
87 $context->response->output('Hello World!');
90 Now http://localhost:3000/hello prints "Hello World!".
92 =item * B<Support for CGI, mod_perl, Apache::Request>
94 Use L<Catalyst::Engine::Apache> or L<Catalyst::Engine::CGI>.
100 The best part is that Catalyst implements all this flexibility in a very simple
105 =item * B<Building Block Interface>
107 Components interoperate very smoothly. For example, Catalyst automatically makes
108 a L<Context> object available to every component. Via the context, you can
109 access the request object, share data between components, and control the flow
110 of your application. Building a Catalyst application feels a lot like snapping
111 together toy building blocks, and everything just works.
113 =item * B<Component Auto-Discovery>
115 No need to C<use> all of your components. Catalyst automatically finds and loads
118 =item * B<Pre-Built Components for Popular Modules>
120 See L<Catalyst::Model::CDBI> for L<Class::DBI>, or L<Catalyst::View::TT> for
121 L<Template Toolkit|Template>. You can even get an instant web database front end
122 with L<Catalyst::Model::CDBI::CRUD>.
124 =item * B<Built-in Test Framework>
126 Catalyst comes with a built-in, lightweight http server and test framework,
127 making it easy to test applications from the command line.
129 =item * B<Helper Scripts>
131 Catalyst provides helper scripts to quickly generate running starter code for
132 components and unit tests.
138 Here's how to install Catalyst and get a simple application up and running,
139 using the helper scripts described above.
143 $ perl -MCPAN -e 'install Bundle::Catalyst'
150 $ script/myapp_create.pl controller Library::Login
154 $ script/myapp_server.pl
156 Now visit these locations with your favorite browser or user agent to see
161 =item http://localhost:3000/
163 =item http://localhost:3000/library/login/
171 Let's see how Catalyst works, by taking a closer look at the components and
172 other parts of a Catalyst application.
174 =head3 Application Class
176 In addition to the Model, View, and Controller components, there's a single
177 class that represents your application itself. This is where you configure your
178 application, load plugins, define application-wide actions, and extend Catalyst.
183 use Catalyst qw/-Debug/;
186 name => 'My Application',
187 root => '/home/joeuser/myapp/root',
189 # You can put anything else you want in here:
190 my_configuration_variable => 'something',
193 sub default : Private {
194 my ( $self, $context ) = @_;
195 $context->response->output('Catalyst rockz!');
200 For most applications, Catalyst requires you to define only two config
207 Name of your application.
211 Path to additional files such as templates, images, or other static data.
215 However, you can define as many parameters as you want for plugins or whatever
216 you need. You can access them anywhere in your application via
217 C<$context-E<gt>config-E<gt>{$param_name}>.
221 Catalyst automatically blesses a Context object into your application class and
222 makes it available everywhere in your application. Use the Context to directly
223 interact with Catalyst and glue your L<Components> together. For example, if you
224 need to use the Context from within a Template Toolkit template, it's already
227 <h1>Welcome to [% c.config.name %]!</h1>
229 As illustrated earlier in our URL-to-Action dispatching example, the Context is
230 always the second method parameter, behind the Component object reference or
231 class name itself. Previously we called it C<$context> for clarity, but most
232 Catalyst developers just call it C<$c>:
235 my ( $self, $c ) = @_;
236 $c->res->output('Hello World!');
239 The Context contains several important objects:
243 =item * L<Catalyst::Request>
248 The request object contains all kinds of request-specific information, like
249 query parameters, cookies, uploads, headers, and more.
251 $c->req->params->{foo};
252 $c->req->cookies->{sessionid};
253 $c->req->headers->content_type;
256 =item * L<Catalyst::Response>
261 The response is like the request, but contains just response-specific
264 $c->res->output('Hello World');
265 $c->res->status(404);
266 $c->res->redirect('http://oook.de');
268 =item * L<Catalyst::Config>
275 =item * L<Catalyst::Log>
279 $c->log->debug('Something happened');
280 $c->log->info('Something you should know');
286 $c->stash->{foo} = 'bar';
290 The last of these, the stash, is a universal hash for sharing data among
291 application components. For an example, we return to our 'hello' action:
294 my ( $self, $c ) = @_;
295 $c->stash->{message} = 'Hello World!';
296 $c->forward('show_message');
299 sub show_message : Private {
300 my ( $self, $c ) = @_;
301 $c->res->output( $c->stash->{message} );
304 Note that the stash should be used only for passing data in an individual
305 request cycle; it gets cleared at a new request. If you need to maintain more
306 persistent data, use a session.
310 A Catalyst controller is defined by its actions. An action is a sub with a
311 special attribute. You've already seen some examples of actions in this
312 document. The URL (for example http://localhost.3000/foo/bar) consists of two
313 parts, the base (http://localhost:3000/ in this example) and the path (foo/bar).
314 Please note that the trailing slash after the hostname[:port] always belongs to
315 base and not to the action.
317 Catalyst supports several types of actions:
323 sub bar : Path('foo/bar') { }
325 Matches only http://localhost:3000/foo/bar.
329 sub bar : Regex('^item(\d+)/order(\d+)$') { }
331 Matches any URL that matches the pattern in the action key, e.g.
332 http://localhost:3000/item23/order42. The '' around the regexp is optional, but
333 perltidy likes it. :)
335 Regex matches act globally, i.e. without reference to the namespace from which
336 it is called, so that a C<bar> method in the
337 C<MyApp::Controller::Catalog::Order::Process> namespace won't match any form of
338 C<bar>, C<Catalog>, C<Order>, or C<Process> unless you explicitly put this in
341 If you use capturing parentheses to extract values within the matching URL (23,
342 42 in the above example), those values are available in the $c->req->snippets
343 array. If you want to pass arguments at the end of your URL, you must use regex
344 action keys. See L</URL Argument Handling> below.
351 Matches http://localhost:3000/foo. The function name is mapped directly
352 to the application base.
354 =item * B<Namespace-Prefixed>
356 package MyApp::C::My::Controller;
359 Matches http://localhost:3000/my/controller/foo.
361 This action type indicates that the matching URL must be prefixed with a
362 modified form of the component's class (package) name. This modified class name
363 excludes the parts that have a pre-defined meaning in Catalyst ("MyApp::C" in
364 the above example), replaces "::" with "/", and converts the name to lower case.
365 See L</Components> for a full explanation of the pre-defined meaning of Catalyst
366 component class names.
370 sub foo : Private { }
372 Matches no URL, and cannot be executed by requesting a URL that corresponds to
373 the action key. Private actions can be executed only inside a Catalyst
374 application, by calling the C<forward> method:
378 See L</Flow Control> for a full explanation of C<forward>. Note that, as
379 discussed there, when forwarding from another component, you must use the
380 absolute path to the method, so that a private C<bar> method in your
381 C<MyApp::Controller::Catalog::Order::Process> controller must, if called from
382 elsewhere, be reach with C<$c-E<gt>forward('/catalog/order/process/bar')>.
386 B<Note:> After seeing these examples, you probably wonder what the point
387 is of defining names for regex and path actions. Actually, every public
388 action is also a private one, so you have one unified way of addressing
389 components in your C<forward>s.
391 =head4 Built-in Private Actions
393 In response to specific application states, Catalyst will automatically call
394 these built-in private actions:
398 =item * B<default : Private>
400 Called when no other action matches.
402 =item * B<begin : Private>
404 Called at the beginning of a request, before any matching actions are called.
406 =item * B<end : Private>
410 Called at the end of a request, after all matching actions are called.
412 =head4 B<Built-in actions in controllers/autochaining>
414 Package MyApp::C::Foo;
415 sub begin : Private { }
416 sub default : Private { }
418 You can define the Built-in Private Actions within your controllers as
419 well. The actions will override the ones in lower level controllers or
420 your global application.
422 In addition to the normal built-ins, you have a special action for
423 making inheritance chains, 'auto'. These will be run after C<begin>,
424 but before your action is processed.
428 =item for a request for /foo/foo
432 MyApp::C::Foo::default
435 =item for a request for /foo/bar/foo
437 MyApp::C::Foo::Bar::begin
440 MyApp::C::Foo::Bar::default
441 MyApp::C::Foo::Bar::end
445 Also, if you need to break out of the chain in one of your auto
446 actions, you can return 0, if so, your action will not be processed,
447 but the end will, so for the request above, if the first auto returns
448 false, it would look like this:
452 =item for a request for /foo/bar/foo where auto returns false
454 MyApp::C::Foo::Bar::begin
456 MyApp::C::Foo::Bar::end
460 B<Note:> auto actions have to return a true value to continue
461 processing! You can also die in the autochain action, in that case, the
462 request will go straight to the finalize stage, without processing
466 =head4 B<URL Argument Handling>
468 If you want to pass variable arguments at the end of a URL, you must use regex
469 actions keys with '^' and '$' anchors, and the arguments must be separated with
470 forward slashes (/) in the URL. For example, suppose you want to handle
471 /foo/$bar/$baz, where $bar and $baz may vary:
473 sub foo : Regex('^foo$') { my ($self, $context, $bar, $baz) = @_; }
475 But what if you also defined actions for /foo/boo and /foo/boo/hoo ?
477 sub boo : Path('foo/boo') { .. }
478 sub hoo : Path('foo/boo/hoo') { .. }
480 Catalyst matches actions in most specific to least specific order:
484 /foo # might be /foo/bar/baz
486 So Catalyst would never mistakenly dispatch the first two URLs to the '^foo$' action.
490 You control the application flow with the C<forward> method, which accepts the
491 key of an action to execute.
494 my ( $self, $c ) = @_;
495 $c->stash->{message} = 'Hello World!';
496 $c->forward('check_message');
499 sub check_message : Private {
500 my ( $self, $c ) = @_;
501 return unless $c->stash->{message};
502 $c->forward('show_message');
505 sub show_message : Private {
506 my ( $self, $c ) = @_;
507 $c->res->output( $c->stash->{message} );
510 As you can see from these examples, you can just use the method name as long as
511 you are referring to methods in the same controller. If you want to forward to a
512 method in another controller, or the main application, you will have to refer to
513 the method by absolute path.
515 $c->forward('/my/controller/action');
516 $c->forward('/default');
518 You can also forward to classes and methods.
521 my ( $self, $c ) = @_;
522 $c->forward(qw/MyApp::M::Hello say_hello/);
526 my ( $self, $c ) = @_;
527 $c->forward('MyApp::M::Hello');
530 package MyApp::M::Hello;
533 my ( $self, $c ) = @_;
534 $c->res->output('Hello World!');
538 my ( $self, $c ) = @_;
539 $c->res->output('Goodbye World!');
542 Note that C<forward> returns to the calling action and continues processing
543 after the action finishes. Catalyst will automatically try to call process() if
548 Catalyst has an uncommonly flexible component system. You can define as many
549 L<Models>, L<Views>, and L<Controllers> as you like.
551 All components must inherit from L<Catalyst::Base>, which provides a simple
552 class structure and some common class methods like C<config> and C<new>
555 package MyApp::C::Catalog;
558 use base 'Catalyst::Base';
560 __PACKAGE__->config( foo => 'bar' );
564 You don't have to C<use> or otherwise register Models, Views, and Controllers.
565 Catalyst automatically discovers and instantiates them when you call C<setup> in
566 the main application. All you need to do is put them in directories named for
567 each Component type. Notice that you can use some very terse aliases for each
572 =item * B<MyApp/Model/>
576 =item * B<MyApp/View/>
580 =item * B<MyApp/Controller/>
588 To show how to define views, we'll use an already-existing base class for the
589 L<Template Toolkit|Template>, L<Catalyst::View::TT>. All we need to do is
590 inherit from this class:
592 package MyApp::V::TT;
595 use base 'Catalyst::View::TT';
599 (You can also generate this automatically by using the helper script:
601 script/myapp_create.pl view TT TT
603 where the first C<TT> tells the script to create a Template Toolkit
604 view, and the second tells the script that its name should be C<TT>.)
606 This gives us a process() method and we can now just do
607 $c->forward('MyApp::V::TT') to render our templates. The base class makes
608 process() implicit, so we don't have to say C<$c-E<gt>forward(qw/MyApp::V::TT
612 my ( $self, $c ) = @_;
613 $c->stash->{template} = 'hello.tt';
617 my ( $self, $c ) = @_;
618 $c->forward('MyApp::V::TT');
621 You normally render templates at the end of a request, so it's a perfect use for
622 the global C<end> action.
624 Also, be sure to put the template under the directory specified in
625 C<$c-E<gt>config-E<gt>{root}>, or you'll be forced to look at our eyecandy debug
630 To show how to define models, again we'll use an already-existing base class,
631 this time for L<Class::DBI>: L<Catalyst::Model::CDBI>.
633 But first, we need a database.
637 id INTEGER PRIMARY KEY,
642 id INTEGER PRIMARY KEY,
643 foo INTEGER REFERENCES foo,
647 INSERT INTO foo (data) VALUES ('TEST!');
650 % sqlite /tmp/myapp.db < myapp.sql
652 Now we can create a CDBI component for this database.
654 package MyApp::M::CDBI;
657 use base 'Catalyst::Model::CDBI';
660 dsn => 'dbi:SQLite:/tmp/myapp.db',
666 Catalyst automatically loads table layouts and relationships. Use the stash to
667 pass data to your templates.
672 use Catalyst '-Debug';
675 name => 'My Application',
676 root => '/home/joeuser/myapp/root'
682 my ( $self, $c ) = @_;
683 $c->stash->{template} ||= 'index.tt';
684 $c->forward('MyApp::V::TT');
688 my ( $self, $c, $id ) = @_;
689 $c->stash->{item} = MyApp::M::CDBI::Foo->retrieve($id);
694 The id is [% item.data %]
698 Multiple controllers are a good way to separate logical domains of your
701 package MyApp::C::Login;
704 new-password : Local { }
707 package MyApp::C::Catalog;
712 package MyApp::C::Cart;
715 sub update : Local { }
716 sub order : Local { }
720 Catalyst has a built-in http server for testing! (Later, you can easily use a
721 more powerful server, e.g. Apache/mod_perl, in a production environment.)
723 Start your application on the command line...
725 script/myapp_server.pl
727 ...then visit http://localhost:3000/ in a browser to view the output.
729 You can also do it all from the command line:
731 script/myapp_test.pl http://localhost/
739 Join #catalyst on irc.perl.org.
743 http://lists.rawmode.org/mailman/listinfo/catalyst
744 http://lists.rawmode.org/mailman/listinfo/catalyst-dev
748 Sebastian Riedel, C<sri@oook.de>
749 David Naughton, C<naughton@umn.edu>
750 Marcus Ramberg, C<mramberg@cpan.org>
751 Jesse Sheidlower, C<jester@panix.com>
752 Danijel Milicevic, C<me@danijel.de>
756 This program is free software, you can redistribute it and/or modify it under
757 the same terms as Perl itself.