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
47 out the original book on the subject, I<Design Patterns>, by Gamma,
48 Helm, Johnson, and Vlissides, also known as the Gang of Four (GoF). You
49 can also just Google it. Many, many web application frameworks are
50 based on MVC, including all those listed above.
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->body('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',
188 # You can put anything else you want in here:
189 my_configuration_variable => 'something',
192 sub default : Private {
193 my ( $self, $context ) = @_;
194 $context->response->body('Catalyst rockz!');
199 For most applications, Catalyst requires you to define only one config
206 Name of your application.
210 Optionally, you can specify a B<root> parameter for templates and static data.
211 If omitted, Catalyst will try to auto-detect the directory's location. You
212 can define as many parameters as you want for plugins or whatever you
213 need. You can access them anywhere in your application
214 via C<$context-E<gt>config-E<gt>{$param_name}>.
218 Catalyst automatically blesses a Context object into your application class and
219 makes it available everywhere in your application. Use the Context to directly
220 interact with Catalyst and glue your L<Components> together. For example, if you
221 need to use the Context from within a Template Toolkit template, it's already
224 <h1>Welcome to [% c.config.name %]!</h1>
226 As illustrated earlier in our URL-to-Action dispatching example, the Context is
227 always the second method parameter, behind the Component object reference or
228 class name itself. Previously we called it C<$context> for clarity, but most
229 Catalyst developers just call it C<$c>:
232 my ( $self, $c ) = @_;
233 $c->res->body('Hello World!');
236 The Context contains several important objects:
240 =item * L<Catalyst::Request>
245 The request object contains all kinds of request-specific information, like
246 query parameters, cookies, uploads, headers, and more.
248 $c->req->params->{foo};
249 $c->req->cookies->{sessionid};
250 $c->req->headers->content_type;
253 =item * L<Catalyst::Response>
258 The response is like the request, but contains just response-specific
261 $c->res->body('Hello World');
262 $c->res->status(404);
263 $c->res->redirect('http://oook.de');
265 =item * L<Catalyst::Config>
272 =item * L<Catalyst::Log>
276 $c->log->debug('Something happened');
277 $c->log->info('Something you should know');
283 $c->stash->{foo} = 'bar';
287 The last of these, the stash, is a universal hash for sharing data among
288 application components. For an example, we return to our 'hello' action:
291 my ( $self, $c ) = @_;
292 $c->stash->{message} = 'Hello World!';
293 $c->forward('show_message');
296 sub show_message : Private {
297 my ( $self, $c ) = @_;
298 $c->res->body( $c->stash->{message} );
301 Note that the stash should be used only for passing data in an individual
302 request cycle; it gets cleared at a new request. If you need to maintain more
303 persistent data, use a session.
307 A Catalyst controller is defined by its actions. An action is a sub with a
308 special attribute. You've already seen some examples of actions in this
309 document. The URL (for example http://localhost.3000/foo/bar) consists of two
310 parts, the base (http://localhost:3000/ in this example) and the path (foo/bar).
311 Please note that the trailing slash after the hostname[:port] always belongs to
312 base and not to the action.
314 Catalyst supports several types of actions:
320 sub bar : Path('foo/bar') { }
322 Matches only http://localhost:3000/foo/bar.
326 sub bar : Regex('^item(\d+)/order(\d+)$') { }
328 Matches any URL that matches the pattern in the action key, e.g.
329 http://localhost:3000/item23/order42. The '' around the regexp is optional, but
330 perltidy likes it. :)
332 Regex matches act globally, i.e. without reference to the namespace from which
333 it is called, so that a C<bar> method in the
334 C<MyApp::Controller::Catalog::Order::Process> namespace won't match any form of
335 C<bar>, C<Catalog>, C<Order>, or C<Process> unless you explicitly put this in
336 the regex. To achieve the above, you should consider using a C<LocalRegex> action.
338 =item * B<LocalRegex>
340 sub bar : LocalRegex('^widget(\d+)$') { }
342 LocalRegex actions act locally. If you were to use C<bar> in
343 C<MyApp::Controller::Catalogue>, the above example would match urls like
344 http://localhost:3000/catalogue/widget23.
346 For both LocalRegex and Regex actions, if you use capturing parentheses to
347 extract values within the matching URL ("widget23" would capture "23" in the
348 above example), those values are available in the $c->req->snippets
349 array. If you want to pass arguments at the end of your URL, you must use regex
350 action keys. See L</URL Argument Handling> below.
357 Matches http://localhost:3000/foo. The function name is mapped directly
358 to the application base.
360 =item * B<Namespace-Prefixed>
362 package MyApp::C::My::Controller;
365 Matches http://localhost:3000/my/controller/foo.
367 This action type indicates that the matching URL must be prefixed with a
368 modified form of the component's class (package) name. This modified class name
369 excludes the parts that have a pre-defined meaning in Catalyst ("MyApp::C" in
370 the above example), replaces "::" with "/", and converts the name to lower case.
371 See L</Components> for a full explanation of the pre-defined meaning of Catalyst
372 component class names.
376 sub foo : Private { }
378 Matches no URL, and cannot be executed by requesting a URL that corresponds to
379 the action key. Private actions can be executed only inside a Catalyst
380 application, by calling the C<forward> method:
384 See L</Flow Control> for a full explanation of C<forward>. Note that, as
385 discussed there, when forwarding from another component, you must use
386 the absolute path to the method, so that a private C<bar> method in your
387 C<MyApp::Controller::Catalog::Order::Process> controller must, if called
388 from elsewhere, be reached with
389 C<$c-E<gt>forward('/catalog/order/process/bar')>.
393 B<Note:> After seeing these examples, you probably wonder what the point
394 is of defining names for regex and path actions. Actually, every public
395 action is also a private one, so you have one unified way of addressing
396 components in your C<forward>s.
398 =head4 Built-in Private Actions
400 In response to specific application states, Catalyst will automatically
401 call these built-in private actions in your application class:
405 =item * B<default : Private>
407 Called when no other action matches. Could be used, for example, for
408 displaying a generic frontpage for the main app, or an error page for
409 individual controllers.
411 =item * B<index : Private>
413 C<index> is much like C<default> except that it takes no arguments
414 and it is weighted slightly higher in the matching process.
416 =item * B<begin : Private>
418 Called at the beginning of a request, before any matching actions are
421 =item * B<end : Private>
423 Called at the end of a request, after all matching actions are called.
427 =head4 Built-in actions in controllers/autochaining
429 Package MyApp::C::Foo;
430 sub begin : Private { }
431 sub default : Private { }
432 sub auto : Private { }
434 You can define built-in private actions within your controllers as
435 well. The actions will override the ones in less-specific controllers,
436 or your application class. In other words, for each of the three
437 built-in private actions, only one will be run in any request
438 cycle. Thus, if C<MyApp::C::Catalog::begin> exists, it will be run in
439 place of C<MyApp::begin> if you're in the C<catalog> namespace, and
440 C<MyApp::C::Catalog::Order::begin> would override this in turn.
442 In addition to the normal built-in actions, you have a special action
443 for making chains, C<auto>. Such C<auto> actions will be run after any
444 C<begin>, but before your action is processed. Unlike the other
445 built-ins, C<auto> actions I<do not> override each other; they will be
446 called in turn, starting with the application class and going through to
447 the I<most> specific class. I<This is the reverse of the order in which
448 the normal built-ins override each other>.
450 Here are some examples of the order in which the various built-ins
455 =item for a request for C</foo/foo>
459 MyApp::C::Foo::default # in the absence of MyApp::C::Foo::Foo
462 =item for a request for C</foo/bar/foo>
464 MyApp::C::Foo::Bar::begin
467 MyApp::C::Foo::Bar::auto
468 MyApp::C::Foo::Bar::default # for MyApp::C::Foo::Bar::foo
469 MyApp::C::Foo::Bar::end
473 The C<auto> action is also distinguished by the fact that you can break
474 out of the processing chain by returning 0. If an C<auto> action returns
475 0, any remaining actions will be skipped, except for C<end>. So, for the
476 request above, if the first auto returns false, the chain would look
481 =item for a request for C</foo/bar/foo> where first C<auto> returns
484 MyApp::C::Foo::Bar::begin
486 MyApp::C::Foo::Bar::end
490 An example of why one might use this is an authentication action: you
491 could set up a C<auto> action to handle authentication in your
492 application class (which will always be called first), and if
493 authentication fails, returning 0 would skip any remaining methods
496 B<Note:> Looking at it another way, C<auto> actions have to return a
497 true value to continue processing! You can also C<die> in the autochain
498 action; in that case, the request will go straight to the finalize
499 stage, without processing further actions.
501 =head4 URL Path Handling
503 You can pass variable arguments as part of the URL path. In this case,
504 you must use regex action keys with '^' and '$' anchors, and the
505 arguments must be separated with forward slashes (/) in the URL. For
506 example, suppose you want to handle C</foo/$bar/$baz>, where C<$bar> and
509 sub foo : Regex('^foo$') { my ($self, $context, $bar, $baz) = @_; }
511 But what if you also defined actions for C</foo/boo> and C</foo/boo/hoo>?
513 sub boo : Path('foo/boo') { .. }
514 sub hoo : Path('foo/boo/hoo') { .. }
516 Catalyst matches actions in most specific to least specific order:
520 /foo # might be /foo/bar/baz but won't be /foo/boo/hoo
522 So Catalyst would never mistakenly dispatch the first two URLs to the
525 =head4 Parameter Processing
527 Parameters passed in the URL query string are handled with methods in
528 the L<Catalyst::Request> class. The C<param> method is functionally
529 equivalent to the C<param> method of C<CGI.pm> and can be used in
530 modules that require this.
532 # http://localhost:3000/catalog/view/?category=hardware&page=3
533 my $category = $c->req->param('category');
534 my $current_page = $c->req->param('page') || 1;
536 # multiple values for single parameter name
537 my @values = $c->req->param('scrolling_list');
539 # DFV requires a CGI.pm-like input hash
540 my $results = Data::FormValidator->check($c->req->params, \%dfv_profile);
544 You control the application flow with the C<forward> method, which
545 accepts the key of an action to execute. This can be an action in the
546 same or another Catalyst controller, or a Class name, optionally
547 followed by a method name. After a C<forward>, the control flow will
548 return to the method from which the C<forward> was issued.
550 A C<forward> is similar to a method call. The main differences are that
551 it wraps the call in an C<eval> to allow exception handling; it
552 automatically passes along the context object (C<$c> or C<$context>);
553 and it allows profiling of each call (displayed in the log with
557 my ( $self, $c ) = @_;
558 $c->stash->{message} = 'Hello World!';
559 $c->forward('check_message'); # $c is automatically included
562 sub check_message : Private {
563 my ( $self, $c ) = @_;
564 return unless $c->stash->{message};
565 $c->forward('show_message');
568 sub show_message : Private {
569 my ( $self, $c ) = @_;
570 $c->res->body( $c->stash->{message} );
573 A C<forward> does not create a new request, so your request
574 object (C<$c-E<gt>req>) will remain unchanged. This is a
575 key difference between using C<forward> and issuing a
578 You can pass new arguments to a C<forward> by adding them
579 in an anonymous array. In this case C<$c-E<gt>req-E<gt>args>
580 will be changed for the duration of the C<forward> only; upon
581 return, the original value of C<$c-E<gt>req-E<gt>args> will
585 my ( $self, $c ) = @_;
586 $c->stash->{message} = 'Hello World!';
587 $c->forward('check_message',[qw/test1/]);
588 # now $c->req->args is back to what it was before
591 sub check_message : Private {
592 my ( $self, $c ) = @_;
593 my $first_argument = $c->req->args[0]; # now = 'test1'
597 As you can see from these examples, you can just use the method name as
598 long as you are referring to methods in the same controller. If you want
599 to forward to a method in another controller, or the main application,
600 you will have to refer to the method by absolute path.
602 $c->forward('/my/controller/action');
603 $c->forward('/default'); # calls default in main application
605 Here are some examples of how to forward to classes and methods.
608 my ( $self, $c ) = @_;
609 $c->forward(qw/MyApp::M::Hello say_hello/);
613 my ( $self, $c ) = @_;
614 $c->forward('MyApp::M::Hello'); # no method: will try 'process'
617 package MyApp::M::Hello;
620 my ( $self, $c ) = @_;
621 $c->res->body('Hello World!');
625 my ( $self, $c ) = @_;
626 $c->res->body('Goodbye World!');
629 Note that C<forward> returns to the calling action and continues
630 processing after the action finishes. If you want all further processing
631 in the calling action to stop, use C<detach> instead, which will execute
632 the C<detach>ed action and not return to the calling sub. In both cases,
633 Catalyst will automatically try to call process() if you omit the
638 Catalyst has an uncommonly flexible component system. You can define as many
639 L<Models>, L<Views>, and L<Controllers> as you like.
641 All components must inherit from L<Catalyst::Base>, which provides a simple
642 class structure and some common class methods like C<config> and C<new>
645 package MyApp::C::Catalog;
648 use base 'Catalyst::Base';
650 __PACKAGE__->config( foo => 'bar' );
654 You don't have to C<use> or otherwise register Models, Views, and
655 Controllers. Catalyst automatically discovers and instantiates them
656 when you call C<setup> in the main application. All you need to do is
657 put them in directories named for each Component type. Notice that you
658 can use some very terse aliases for each one.
662 =item * B<MyApp/Model/>
666 =item * B<MyApp/View/>
670 =item * B<MyApp/Controller/>
678 To show how to define views, we'll use an already-existing base class for the
679 L<Template Toolkit|Template>, L<Catalyst::View::TT>. All we need to do is
680 inherit from this class:
682 package MyApp::V::TT;
685 use base 'Catalyst::View::TT';
689 (You can also generate this automatically by using the helper script:
691 script/myapp_create.pl view TT TT
693 where the first C<TT> tells the script that the name of the view should
694 be C<TT>, and the second that it should be a Template Toolkit view.)
696 This gives us a process() method and we can now just do
697 $c->forward('MyApp::V::TT') to render our templates. The base class makes
698 process() implicit, so we don't have to say C<$c-E<gt>forward(qw/MyApp::V::TT
702 my ( $self, $c ) = @_;
703 $c->stash->{template} = 'hello.tt';
707 my ( $self, $c ) = @_;
708 $c->forward('MyApp::V::TT');
711 You normally render templates at the end of a request, so it's a perfect
712 use for the global C<end> action.
714 Also, be sure to put the template under the directory specified in
715 C<$c-E<gt>config-E<gt>{root}>, or you'll be forced to look at our
716 eyecandy debug screen. ;)
720 To show how to define models, again we'll use an already-existing base class,
721 this time for L<Class::DBI>: L<Catalyst::Model::CDBI>.
723 But first, we need a database.
727 id INTEGER PRIMARY KEY,
732 id INTEGER PRIMARY KEY,
733 foo INTEGER REFERENCES foo,
737 INSERT INTO foo (data) VALUES ('TEST!');
740 % sqlite /tmp/myapp.db < myapp.sql
742 Now we can create a CDBI component for this database.
744 package MyApp::M::CDBI;
747 use base 'Catalyst::Model::CDBI';
750 dsn => 'dbi:SQLite:/tmp/myapp.db',
756 Catalyst automatically loads table layouts and relationships. Use the stash to
757 pass data to your templates.
762 use Catalyst '-Debug';
765 name => 'My Application',
766 root => '/home/joeuser/myapp/root'
772 my ( $self, $c ) = @_;
773 $c->stash->{template} ||= 'index.tt';
774 $c->forward('MyApp::V::TT');
778 my ( $self, $c, $id ) = @_;
779 $c->stash->{item} = MyApp::M::CDBI::Foo->retrieve($id);
784 # Then, in a TT template:
785 The id is [% item.data %]
787 Models do not have to be part of your Catalyst application; you
788 can always call an outside module that serves as your Model:
792 my ( $self, $c ) = @_;
793 $c->stash->{template} = 'list.tt';
794 use Some::Outside::CDBI::Module;
795 my @records = Some::Outside::CDBI::Module->retrieve_all;
796 $c->stash->{records} = \@records;
799 But by using a Model that is part of your Catalyst application, you gain
800 several things: you don't have to C<use> each component, Catalyst will
801 find and load it automatically at compile-time; you can C<forward> to
802 the module, which can only be done to Catalyst components; and only
803 Catalyst components can be fetched with
804 C<$c-E<gt>comp('MyApp::M::SomeModel')>.
806 Happily, since many people have existing Model classes that they
807 would like to use with Catalyst (or, conversely, they want to
808 write Catalyst models that can be used outside of Catalyst, e.g.
809 in a cron job), it's trivial to write a simple component in
810 Catalyst that slurps in an outside Model:
812 package MyApp::M::Catalog;
813 use base qw/Catalyst::Base Some::Other::CDBI::Module::Catalog/;
816 and that's it! Now C<Some::Other::CDBI::Module::Catalog> is part of your
817 Cat app as C<MyApp::M::Catalog>.
821 Multiple controllers are a good way to separate logical domains of your
824 package MyApp::C::Login;
826 sub sign-in : Local { }
827 sub new-password : Local { }
828 sub sign-out : Local { }
830 package MyApp::C::Catalog;
835 package MyApp::C::Cart;
838 sub update : Local { }
839 sub order : Local { }
843 Catalyst has a built-in http server for testing! (Later, you can easily use a
844 more powerful server, e.g. Apache/mod_perl, in a production environment.)
846 Start your application on the command line...
848 script/myapp_server.pl
850 ...then visit http://localhost:3000/ in a browser to view the output.
852 You can also do it all from the command line:
854 script/myapp_test.pl http://localhost/
862 Join #catalyst on irc.perl.org.
866 http://lists.rawmode.org/mailman/listinfo/catalyst
867 http://lists.rawmode.org/mailman/listinfo/catalyst-dev
871 Sebastian Riedel, C<sri@oook.de>
872 David Naughton, C<naughton@umn.edu>
873 Marcus Ramberg, C<mramberg@cpan.org>
874 Jesse Sheidlower, C<jester@panix.com>
875 Danijel Milicevic, C<me@danijel.de>
879 This program is free software, you can redistribute it and/or modify it under
880 the same terms as Perl itself.