3 Catalyst::Manual::Intro - Introduction to Catalyst
7 This is a brief introduction to Catalyst. It explains the most important
8 features of how Catalyst works and shows how to get a simple application
9 up and running quickly. For an introduction (without code) to Catalyst
10 itself, and why you should be using it, see L<Catalyst::Manual::About>.
11 For a systematic step-by-step introduction to writing an application
12 with Catalyst, see L<Catalyst::Manual::Tutorial>.
14 =head2 What is Catalyst?
16 Catalyst is an elegant web application framework, extremely flexible
17 yet extremely simple. It's similar to Ruby on Rails, Spring (Java),
18 and L<Maypole>, upon which it was originally based. Its most important
19 design philosphy is to provide easy access to all the tools you need
20 to develop web applications, with few restrictions on how you need to
21 use these tools. However, this does mean that it is always possible to
22 do things in a different way. Other web frameworks are B<initially>
23 simpler to use, but achieve this by locking the programmer into a
24 single set of tools. Catalyst's emphasis on flexibility means that you
25 have to think more to use it. We view this as a feature. For example,
26 this leads to Catalyst being more suited to system integration tasks
27 than other web frameworks.
31 Catalyst follows the Model-View-Controller (MVC) design pattern,
32 allowing you to easily separate concerns, like content, presentation,
33 and flow control, into separate modules. This separation allows you to
34 modify code that handles one concern without affecting code that handles
35 the others. Catalyst promotes the re-use of existing Perl modules that
36 already handle common web application concerns well.
38 Here's how the Model, View, and Controller map to those concerns, with
39 examples of well-known Perl modules you may want to use for each.
45 Access and modify content (data). L<DBIx::Class>, L<Class::DBI>,
46 L<Xapian>, L<Net::LDAP>...
50 Present content to the user. L<Template Toolkit|Template>,
51 L<Mason|HTML::Mason>, L<HTML::Template>...
55 Control the whole request phase, check parameters, dispatch actions, flow
56 control. Catalyst itself!
60 If you're unfamiliar with MVC and design patterns, you may want to
61 check out the original book on the subject, I<Design Patterns>, by
62 Gamma, Helm, Johnson, and Vlissides, also known as the Gang of Four
63 (GoF). Many, many web application frameworks are based on MVC, which
64 is becoming a popular design paradigm for the world wide web.
68 Catalyst is much more flexible than many other frameworks. Rest assured
69 you can use your favorite Perl modules with Catalyst.
73 =item * B<Multiple Models, Views, and Controllers>
75 To build a Catalyst application, you handle each type of concern inside
76 special modules called L</Components>. Often this code will be very
77 simple, just calling out to Perl modules like those listed above under
78 L</MVC>. Catalyst handles these components in a very flexible way. Use
79 as many Models, Views, and Controllers as you like, using as many
80 different Perl modules as you like, all in the same application. Want to
81 manipulate multiple databases, and retrieve some data via LDAP? No
82 problem. Want to present data from the same Model using L<Template
83 Toolkit|Template> and L<PDF::Template>? Easy.
85 =item * B<Reuseable Components>
87 Not only does Catalyst promote the re-use of already existing Perl
88 modules, it also allows you to re-use your Catalyst components in
89 multiple Catalyst applications.
91 =item * B<Unrestrained URL-to-Action Dispatching>
93 Catalyst allows you to dispatch any URLs to any application L</Actions>,
94 even through regular expressions! Unlike most other frameworks, it
95 doesn't require mod_rewrite or class and method names in URLs.
97 With Catalyst you register your actions and address them directly. For
101 my ( $self, $context ) = @_;
102 $context->response->body('Hello World!');
105 Now http://localhost:3000/hello prints "Hello World!".
107 =item * B<Support for CGI, mod_perl, Apache::Request, FastCGI>
109 Use L<Catalyst::Engine::Apache> or L<Catalyst::Engine::CGI>. Other
110 engines are also available.
116 The best part is that Catalyst implements all this flexibility in a very
121 =item * B<Building Block Interface>
123 Components interoperate very smoothly. For example, Catalyst
124 automatically makes a L</Context> object available to every
125 component. Via the context, you can access the request object, share
126 data between components, and control the flow of your
127 application. Building a Catalyst application feels a lot like snapping
128 together toy building blocks, and everything just works.
130 =item * B<Component Auto-Discovery>
132 No need to C<use> all of your components. Catalyst automatically finds
135 =item * B<Pre-Built Components for Popular Modules>
137 See L<Catalyst::Model::DBIC::Schema> for L<DBIx::Class>, or
138 L<Catalyst::View::TT> for L<Template Toolkit|Template>.
140 =item * B<Built-in Test Framework>
142 Catalyst comes with a built-in, lightweight http server and test
143 framework, making it easy to test applications from the web browser,
144 and the command line.
146 =item * B<Helper Scripts>
148 Catalyst provides helper scripts to quickly generate running starter
149 code for components and unit tests. Install L<Catalyst::Devel> and see
156 Here's how to install Catalyst and get a simple application up and
157 running, using the helper scripts described above.
161 Installation of Catalyst can be a time-consuming and frustrating
162 effort, due to its large number of dependencies. The easiest way
163 to get up and running is to use Matt Trout's C<cat-install>
164 script, from L<http://www.shadowcatsystems.co.uk/static/cat-install>,
165 and then install L<Catalyst::Devel>.
168 # perl -MCPAN -e 'install Catalyst::Devel'
175 $ script/myapp_create.pl controller Library::Login
179 $ script/myapp_server.pl
181 Now visit these locations with your favorite browser or user agent to see
184 (NOTE: Although we create a controller here, we don't actually use it.
185 Both of these URLs should take you to the welcome page.)
190 =item http://localhost:3000/
192 =item http://localhost:3000/library/login/
198 Let's see how Catalyst works, by taking a closer look at the components
199 and other parts of a Catalyst application.
203 Catalyst has an uncommonly flexible component system. You can define as
204 many L</Models>, L</Views>, and L</Controllers> as you like. As discussed
205 previously, the general idea is that the View is responsible for the
206 output of data to the user (typically via a web browser, but a View can
207 also generate PDFs or e-mails, for example); the Model is responsible
208 for providing data (typically from a relational database); and the
209 Controller is responsible for interacting with the user and deciding
210 how user input determines what actions the application takes.
212 In the world of MVC, there are frequent discussions and disagreements
213 about the nature of each element - whether certain types of logic
214 belong in the Model or the Controller, etc. Catalyst's flexibility
215 means that this decision is entirely up to you, the programmer;
216 Catalyst doesn't enforce anything. See L<Catalyst::Manual::About> for
217 a general discussion of these issues.
219 All components must inherit from L<Catalyst::Base>, which provides a
220 simple class structure and some common class methods like C<config> and
221 C<new> (constructor).
223 package MyApp::Controller::Catalog;
226 use base 'Catalyst::Base';
228 __PACKAGE__->config( foo => 'bar' );
232 You don't have to C<use> or otherwise register Models, Views, and
233 Controllers. Catalyst automatically discovers and instantiates them
234 when you call C<setup> in the main application. All you need to do is
235 put them in directories named for each Component type. You can use a
236 short alias for each one.
240 =item * B<MyApp/Model/>
244 =item * B<MyApp/View/>
248 =item * B<MyApp/Controller/>
254 In older versions of Catalyst, the recommended practice (and the one
255 automatically created by helper scripts) was to name the directories
256 C<M/>, C<V/>, and C<C/>. Though these still work, we now recommend
257 the use of the full names.
261 To show how to define views, we'll use an already-existing base class for the
262 L<Template Toolkit|Template>, L<Catalyst::View::TT>. All we need to do is
263 inherit from this class:
265 package MyApp::View::TT;
268 use base 'Catalyst::View::TT';
272 (You can also generate this automatically by using the helper script:
274 script/myapp_create.pl view TT TT
276 where the first C<TT> tells the script that the name of the view should
277 be C<TT>, and the second that it should be a Template Toolkit view.)
279 This gives us a process() method and we can now just do
280 $c->forward('MyApp::View::TT') to render our templates. The base class
281 makes process() implicit, so we don't have to say
282 C<$c-E<gt>forward(qw/MyApp::View::TT process/)>.
285 my ( $self, $c ) = @_;
286 $c->stash->{template} = 'hello.tt';
290 my ( $self, $c ) = @_;
291 $c->forward( $c->view('TT') );
294 You normally render templates at the end of a request, so it's a perfect
295 use for the global C<end> action.
297 In practice, however, you would use a default C<end> action as supplied
298 by L<Catalyst::Action::RenderView>.
300 Also, be sure to put the template under the directory specified in
301 C<$c-E<gt>config-E<gt>{root}>, or you'll end up looking at the debug
306 Models are providers of data. This data could come from anywhere - a
307 search engine index, a spreadsheet, the file system - but typically a
308 Model represents a database table. The data source does not
309 intrinsically have much to do with web applications or Catalyst - it
310 could just as easily be used to write an offline report generator or a
313 To show how to define models, again we'll use an already-existing base
314 class, this time for L<DBIx::Class>: L<Catalyst::Model::DBIC::Schema>.
315 We'll also need L<DBIx::Class::Schema::Loader>.
317 But first, we need a database.
321 id INTEGER PRIMARY KEY,
326 id INTEGER PRIMARY KEY,
327 foo INTEGER REFERENCES foo,
331 INSERT INTO foo (data) VALUES ('TEST!');
333 % sqlite /tmp/myapp.db < myapp.sql
335 Now we can create a DBIC::SchemaLoader component for this database.
337 script/myapp_create.pl model DBIC DBIC::SchemaLoader 'dbi:SQLite:/tmp/myapp.db'
339 L<DBIx::Class::Schema::Loader> automatically loads table layouts and
340 relationships. Use the stash to pass data to your templates.
342 We add the following to MyApp/Controller/Root.pm
345 my ( $self, $c, $id ) = @_;
347 $c->stash->{item} = $c->model('DBIC::Foo')->find($id);
353 my ( $self, $c ) = @_;
355 $c->stash->{template} ||= 'index.tt';
356 $c->forward( $c->view('TT') );
359 We then create a new template file "root/index.tt" containing:
361 The Id's data is [% item.data %]
363 Models do not have to be part of your Catalyst application; you
364 can always call an outside module that serves as your Model:
368 my ( $self, $c ) = @_;
370 $c->stash->{template} = 'list.tt';
372 use Some::Outside::Database::Module;
373 my @records = Some::Outside::Database::Module->search({
374 artist => 'Led Zeppelin',
377 $c->stash->{records} = \@records;
380 But by using a Model that is part of your Catalyst application, you
381 gain several things: you don't have to C<use> each component, Catalyst
382 will find and load it automatically at compile-time; you can
383 C<forward> to the module, which can only be done to Catalyst
384 components. Only Catalyst components can be fetched with
385 C<$c-E<gt>model('SomeModel')>.
387 Happily, since many people have existing Model classes that they
388 would like to use with Catalyst (or, conversely, they want to
389 write Catalyst models that can be used outside of Catalyst, e.g.
390 in a cron job), it's trivial to write a simple component in
391 Catalyst that slurps in an outside Model:
393 package MyApp::Model::DB;
394 use base qw/Catalyst::Model::DBIC::Schema/;
396 schema_class => 'Some::DBIC::Schema',
397 connect_info => ['dbi:SQLite:foo.db', '', '', {AutoCommit=>1}]
401 and that's it! Now C<Some::DBIC::Schema> is part of your
402 Cat app as C<MyApp::Model::DB>.
404 Within Catalyst, the common approach to writing a model for your
405 application is wrapping a generic model (e.g. L<DBIx::Class::Schema>, a
406 bunch of XMLs, or anything really) with an object that contains
407 configuration data, convenience methods, and so forth. Thus you
408 will in effect have two models - a wrapper model that knows something
409 about Catalyst and your web application, and a generic model that is
410 totally independent of these needs.
412 Technically, within Catalyst a model is a B<component> - an instance of
413 the model's class belonging to the application. It is important to
414 stress that the lifetime of these objects is per application, not per
417 While the model base class (L<Catalyst::Model>) provides things like
418 C<config> to better integrate the model into the application, sometimes
419 this is not enough, and the model requires access to C<$c> itself.
421 Situations where this need might arise include:
427 Interacting with another model
431 Using per-request data to control behavior
435 Using plugins from a Model (for example L<Catalyst::Plugin::Cache>).
439 From a style perspective it's usually considered bad form to make your
440 model "too smart" about things - it should worry about business logic
441 and leave the integration details to the controllers. If, however, you
442 find that it does not make sense at all to use an auxillary controller
443 around the model, and the model's need to access C<$c> cannot be
444 sidestepped, there exists a power tool called L</ACCEPT_CONTEXT>.
448 Multiple controllers are a good way to separate logical domains of your
451 package MyApp::Controller::Login;
453 use base qw/Catalyst::Controller/;
455 sub login : Path("login") { }
456 sub new_password : Path("new-password") { }
457 sub logout : Path("logout") { }
459 package MyApp::Controller::Catalog;
461 use base qw/Catalyst::Controller/;
466 package MyApp::Controller::Cart;
468 use base qw/Catalyst::Controller/;
471 sub update : Local { }
472 sub order : Local { }
474 Note that you can also supply attributes via the Controller's config so
475 long as you have at least one attribute on a subref to be exported
476 (:Action is commonly used for this) - for example the following is
477 equivalent to the same controller above:
479 package MyApp::Controller::Login;
481 use base qw/Catalyst::Controller/;
485 'sign_in' => { Path => 'sign-in' },
486 'new_password' => { Path => 'new-password' },
487 'sign_out' => { Path => 'sign-out' },
491 sub sign_in : Action { }
492 sub new_password : Action { }
493 sub sign_out : Action { }
495 =head3 ACCEPT_CONTEXT
497 Whenever you call $c->component("Foo") you get back an object - the
498 instance of the model. If the component supports the C<ACCEPT_CONTEXT>
499 method instead of returning the model itself, the return value of C<<
500 $model->ACCEPT_CONTEXT( $c ) >> will be used.
502 This means that whenever your model/view/controller needs to talk to C<$c> it
503 gets a chance to do this when it's needed.
505 A typical C<ACCEPT_CONTEXT> method will either clone the model and return one
506 with the context object set, or it will return a thin wrapper that contains
507 C<$c> and delegates to the per-application model object.
509 A typical C<ACCEPT_CONTEXT> method could look like this:
512 my ( $self, $c, @extra_arguments ) = @_;
513 bless { %$self, c => $c }, ref($self);
516 effectively treating $self as a B<prototype object> that gets a new parameter.
517 C<@extra_arguments> comes from any trailing arguments to
518 C<< $c->component( $bah, @extra_arguments ) >> (or C<< $c->model(...) >>,
519 C<< $c->view(...) >> etc).
521 The life time of this value is B<per usage>, and not per request. To make this
522 per request you can use the following technique:
524 Add a field to C<$c>, like C<my_model_instance>. Then write your
525 C<ACCEPT_CONTEXT> method to look like this:
528 my ( $self, $c ) = @_;
530 if ( my $per_request = $c->my_model_instance ) {
533 my $new_instance = bless { %$self, c => $c }, ref($self);
534 Scalar::Util::weaken($new_instance->{c}); # or we have a circular reference
535 $c->my_model_instance( $new_instance );
536 return $new_instance;
540 =head3 Application Class
542 In addition to the Model, View, and Controller components, there's a
543 single class that represents your application itself. This is where you
544 configure your application, load plugins, and extend Catalyst.
549 use Catalyst qw/-Debug/; # Add other plugins here, e.g.
550 # for session support
553 name => 'My Application',
555 # You can put anything else you want in here:
556 my_configuration_variable => 'something',
560 In older versions of Catalyst, the application class was where you put
561 global actions. However, as of version 5.66, the recommended practice is
562 to place such actions in a special Root controller (see L</Actions>,
563 below), to avoid namespace collisions.
569 The name of your application.
573 Optionally, you can specify a B<root> parameter for templates and static
574 data. If omitted, Catalyst will try to auto-detect the directory's
575 location. You can define as many parameters as you want for plugins or
576 whatever you need. You can access them anywhere in your application via
577 C<$context-E<gt>config-E<gt>{$param_name}>.
581 Catalyst automatically blesses a Context object into your application
582 class and makes it available everywhere in your application. Use the
583 Context to directly interact with Catalyst and glue your L</Components>
584 together. For example, if you need to use the Context from within a
585 Template Toolkit template, it's already there:
587 <h1>Welcome to [% c.config.name %]!</h1>
589 As illustrated in our URL-to-Action dispatching example, the Context is
590 always the second method parameter, behind the Component object
591 reference or class name itself. Previously we called it C<$context> for
592 clarity, but most Catalyst developers just call it C<$c>:
595 my ( $self, $c ) = @_;
596 $c->res->body('Hello World!');
599 The Context contains several important objects:
603 =item * L<Catalyst::Request>
608 The request object contains all kinds of request-specific information, like
609 query parameters, cookies, uploads, headers, and more.
611 $c->req->params->{foo};
612 $c->req->cookies->{sessionid};
613 $c->req->headers->content_type;
615 $c->req->uri_with( { page = $pager->next_page } );
617 =item * L<Catalyst::Response>
622 The response is like the request, but contains just response-specific
625 $c->res->body('Hello World');
626 $c->res->status(404);
627 $c->res->redirect('http://oook.de');
629 =item * L<Catalyst::Config>
635 =item * L<Catalyst::Log>
638 $c->log->debug('Something happened');
639 $c->log->info('Something you should know');
644 $c->stash->{foo} = 'bar';
645 $c->stash->{baz} = {baz => 'qox'};
646 $c->stash->{fred} = [qw/wilma pebbles/];
652 The last of these, the stash, is a universal hash for sharing data among
653 application components. For an example, we return to our 'hello' action:
656 my ( $self, $c ) = @_;
657 $c->stash->{message} = 'Hello World!';
658 $c->forward('show_message');
661 sub show_message : Private {
662 my ( $self, $c ) = @_;
663 $c->res->body( $c->stash->{message} );
666 Note that the stash should be used only for passing data in an
667 individual request cycle; it gets cleared at a new request. If you need
668 to maintain persistent data, use a session. See
669 L<Catalyst::Plugin::Session> for a comprehensive set of
670 Catalyst-friendly session-handling tools.
674 A Catalyst controller is defined by its actions. An action is a
675 subroutine with a special attribute. You've already seen some examples
676 of actions in this document. The URL (for example
677 http://localhost.3000/foo/bar) consists of two parts, the base
678 (http://localhost:3000/ in this example) and the path (foo/bar). Please
679 note that the trailing slash after the hostname[:port] always belongs to
680 base and not to the action.
684 =item * B<Application Wide Actions>
686 Actions which are called at the root level of the application
687 (e.g. http://localhost:3000/ ) go in MyApp::Controller::Root, like
690 package MyApp::Controller::Root;
691 use base 'Catalyst::Controller';
692 # Sets the actions in this controller to be registered with no prefix
693 # so they function identically to actions created in MyApp.pm
694 __PACKAGE__->config->{namespace} = '';
695 sub default : Private {
696 my ( $self, $context ) = @_;
697 $context->response->body('Catalyst rocks!');
705 Catalyst supports several types of actions:
709 =item * B<Literal> (B<Path> actions)
711 package MyApp::Controller::My::Controller;
712 sub bar : Path('foo/bar') { }
714 Literal C<Path> actions will act relative to their current
715 namespace. The above example matches only
716 http://localhost:3000/my/controller/foo/bar. If you start your path with
717 a forward slash, it will match from the root. Example:
719 package MyApp::Controller::My::Controller;
720 sub bar : Path('/foo/bar') { }
722 Matches only http://localhost:3000/foo/bar.
724 package MyApp::Controller::My::Controller;
727 By leaving the C<Path> definition empty, it will match on the namespace
728 root. The above code matches http://localhost:3000/my/controller.
732 sub bar : Regex('^item(\d+)/order(\d+)$') { }
734 Matches any URL that matches the pattern in the action key, e.g.
735 http://localhost:3000/item23/order42. The '' around the regexp is
736 optional, but perltidy likes it. :)
738 Regex matches act globally, i.e. without reference to the namespace from
739 which it is called, so that a C<bar> method in the
740 C<MyApp::Controller::Catalog::Order::Process> namespace won't match any
741 form of C<bar>, C<Catalog>, C<Order>, or C<Process> unless you
742 explicitly put this in the regex. To achieve the above, you should
743 consider using a C<LocalRegex> action.
745 =item * B<LocalRegex>
747 sub bar : LocalRegex('^widget(\d+)$') { }
749 LocalRegex actions act locally. If you were to use C<bar> in
750 C<MyApp::Controller::Catalog>, the above example would match urls like
751 http://localhost:3000/catalog/widget23.
753 If you omit the "C<^>" from your regex, then it will match any depth
754 from the controller and not immediately off of the controller name. The
755 following example differs from the above code in that it will match
756 http://localhost:3000/catalog/foo/widget23 as well.
758 package MyApp::Controller::Catalog;
759 sub bar : LocalRegex('widget(\d+)$') { }
761 For both LocalRegex and Regex actions, if you use capturing parentheses
762 to extract values within the matching URL, those values are available in
763 the C<$c-E<gt>req-E<gt>captures> array. In the above example, "widget23"
764 would capture "23" in the above example, and
765 C<$c-E<gt>req-E<gt>captures-E<gt>[0]> would be "23". If you want to pass
766 arguments at the end of your URL, you must use regex action keys. See
767 L</URL Path Handling> below.
769 =item * B<Top-level> (B<Global>)
771 package MyApp::Controller::Foo;
774 Matches http://localhost:3000/foo. The function name is mapped
775 directly to the application base. You can provide an equivalent
776 function in this case by doing the following:
778 package MyApp::Controller::Root
781 =item * B<Namespace-Prefixed> (B<Local>)
783 package MyApp::Controller::My::Controller;
786 Matches http://localhost:3000/my/controller/foo.
788 This action type indicates that the matching URL must be prefixed with a
789 modified form of the component's class (package) name. This modified
790 class name excludes the parts that have a pre-defined meaning in
791 Catalyst ("MyApp::Controller" in the above example), replaces "::" with
792 "/", and converts the name to lower case. See L</Components> for a full
793 explanation of the pre-defined meaning of Catalyst component class
798 Catalyst also provides a method to build and dispatch chains of actions,
801 sub catalog : Chained : CaptureArgs(1) {
802 my ( $self, $c, $arg ) = @_;
806 sub item : Chained('catalog') : Args(1) {
807 my ( $self, $c, $arg ) = @_;
811 to handle a C</catalog/*/item/*> path. For further information about this
812 dispatch type, please see L<Catalyst::DispatchType::Chained>.
816 sub foo : Private { }
818 Matches no URL, and cannot be executed by requesting a URL that
819 corresponds to the action key. Private actions can be executed only
820 inside a Catalyst application, by calling the C<forward> method:
824 See L</Flow Control> for a full explanation of C<forward>. Note that, as
825 discussed there, when forwarding from another component, you must use
826 the absolute path to the method, so that a private C<bar> method in your
827 C<MyApp::Controller::Catalog::Order::Process> controller must, if called
828 from elsewhere, be reached with
829 C<$c-E<gt>forward('/catalog/order/process/bar')>.
833 Args is not an action type per se, but an action modifier - it adds a
834 match restriction to any action it's provided to, requiring only as many
835 path parts as are specified for the action to be valid - for example in
836 MyApp::Controller::Foo,
840 would match any URL starting /foo/bar/. To restrict this you can do
842 sub bar :Local :Args(1)
844 to only match /foo/bar/*/
848 B<Note:> After seeing these examples, you probably wonder what the point
849 is of defining names for regex and path actions. Every public action is
850 also a private one, so you have one unified way of addressing components
853 =head4 Built-in Private Actions
855 In response to specific application states, Catalyst will automatically
856 call these built-in private actions in your application class:
860 =item * B<default : Private>
862 Called when no other action matches. Could be used, for example, for
863 displaying a generic frontpage for the main app, or an error page for
864 individual controllers.
866 If C<default> isn't acting how you would expect, look at using a
867 L</Literal> C<Path> action (with an empty path string). The difference
868 is that C<Path> takes arguments relative from the namespace and
869 C<default> I<always> takes arguments relative from the root, regardless
870 of what controller it's in. Indeed, this is now the recommended way of
871 handling default situations; the C<default> private controller should
872 be considered deprecated.
874 =item * B<index : Private>
876 C<index> is much like C<default> except that it takes no arguments
877 and it is weighted slightly higher in the matching process. It is
878 useful as a static entry point to a controller, e.g. to have a static
879 welcome page. Note that it's also weighted higher than Path.
881 =item * B<begin : Private>
883 Called at the beginning of a request, before any matching actions are
886 =item * B<end : Private>
888 Called at the end of a request, after all matching actions are called.
892 =head4 Built-in actions in controllers/autochaining
894 Package MyApp::Controller::Foo;
895 sub begin : Private { }
896 sub default : Private { }
897 sub auto : Private { }
899 You can define built-in private actions within your controllers as
900 well. The actions will override the ones in less-specific controllers,
901 or your application class. In other words, for each of the three
902 built-in private actions, only one will be run in any request
903 cycle. Thus, if C<MyApp::Controller::Catalog::begin> exists, it will be
904 run in place of C<MyApp::begin> if you're in the C<catalog> namespace,
905 and C<MyApp::Controller::Catalog::Order::begin> would override this in
908 =item * B<auto : Private>
910 In addition to the normal built-in actions, you have a special action
911 for making chains, C<auto>. Such C<auto> actions will be run after any
912 C<begin>, but before your action is processed. Unlike the other
913 built-ins, C<auto> actions I<do not> override each other; they will be
914 called in turn, starting with the application class and going through to
915 the I<most> specific class. I<This is the reverse of the order in which
916 the normal built-ins override each other>.
918 Here are some examples of the order in which the various built-ins
923 =item for a request for C</foo/foo>
927 MyApp::Controller::Foo::default # in the absence of MyApp::Controller::Foo::Foo
930 =item for a request for C</foo/bar/foo>
932 MyApp::Controller::Foo::Bar::begin
934 MyApp::Controller::Foo::auto
935 MyApp::Controller::Foo::Bar::auto
936 MyApp::Controller::Foo::Bar::default # for MyApp::Controller::Foo::Bar::foo
937 MyApp::Controller::Foo::Bar::end
941 The C<auto> action is also distinguished by the fact that you can break
942 out of the processing chain by returning 0. If an C<auto> action returns
943 0, any remaining actions will be skipped, except for C<end>. So, for the
944 request above, if the first auto returns false, the chain would look
949 =item for a request for C</foo/bar/foo> where first C<auto> returns
952 MyApp::Controller::Foo::Bar::begin
954 MyApp::Controller::Foo::Bar::end
958 An example of why one might use this is an authentication action: you
959 could set up a C<auto> action to handle authentication in your
960 application class (which will always be called first), and if
961 authentication fails, returning 0 would skip any remaining methods
964 B<Note:> Looking at it another way, C<auto> actions have to return a
965 true value to continue processing! You can also C<die> in the auto
966 action; in that case, the request will go straight to the finalize
967 stage, without processing further actions.
969 =head4 URL Path Handling
971 You can pass variable arguments as part of the URL path, separated with
972 forward slashes (/). If the action is a Regex or LocalRegex, the '$' anchor
973 must be used. For example, suppose you want to handle C</foo/$bar/$baz>,
974 where C<$bar> and C<$baz> may vary:
976 sub foo : Regex('^foo$') { my ($self, $context, $bar, $baz) = @_; }
978 But what if you also defined actions for C</foo/boo> and C</foo/boo/hoo>?
980 sub boo : Path('foo/boo') { .. }
981 sub hoo : Path('foo/boo/hoo') { .. }
983 Catalyst matches actions in most specific to least specific order:
987 /foo # might be /foo/bar/baz but won't be /foo/boo/hoo
989 So Catalyst would never mistakenly dispatch the first two URLs to the
992 If a Regex or LocalRegex action doesn't use the '$' anchor, the action will
993 still match a URL containing arguments, however the arguments won't be
996 =head4 Parameter Processing
998 Parameters passed in the URL query string are handled with methods in
999 the L<Catalyst::Request> class. The C<param> method is functionally
1000 equivalent to the C<param> method of C<CGI.pm> and can be used in
1001 modules that require this.
1003 # http://localhost:3000/catalog/view/?category=hardware&page=3
1004 my $category = $c->req->param('category');
1005 my $current_page = $c->req->param('page') || 1;
1007 # multiple values for single parameter name
1008 my @values = $c->req->param('scrolling_list');
1010 # DFV requires a CGI.pm-like input hash
1011 my $results = Data::FormValidator->check($c->req->params, \%dfv_profile);
1015 You control the application flow with the C<forward> method, which
1016 accepts the key of an action to execute. This can be an action in the
1017 same or another Catalyst controller, or a Class name, optionally
1018 followed by a method name. After a C<forward>, the control flow will
1019 return to the method from which the C<forward> was issued.
1021 A C<forward> is similar to a method call. The main differences are that
1022 it wraps the call in an C<eval> to allow exception handling; it
1023 automatically passes along the context object (C<$c> or C<$context>);
1024 and it allows profiling of each call (displayed in the log with
1027 sub hello : Global {
1028 my ( $self, $c ) = @_;
1029 $c->stash->{message} = 'Hello World!';
1030 $c->forward('check_message'); # $c is automatically included
1033 sub check_message : Private {
1034 my ( $self, $c ) = @_;
1035 return unless $c->stash->{message};
1036 $c->forward('show_message');
1039 sub show_message : Private {
1040 my ( $self, $c ) = @_;
1041 $c->res->body( $c->stash->{message} );
1044 A C<forward> does not create a new request, so your request object
1045 (C<$c-E<gt>req>) will remain unchanged. This is a key difference between
1046 using C<forward> and issuing a redirect.
1048 You can pass new arguments to a C<forward> by adding them
1049 in an anonymous array. In this case C<$c-E<gt>req-E<gt>args>
1050 will be changed for the duration of the C<forward> only; upon
1051 return, the original value of C<$c-E<gt>req-E<gt>args> will
1054 sub hello : Global {
1055 my ( $self, $c ) = @_;
1056 $c->stash->{message} = 'Hello World!';
1057 $c->forward('check_message',[qw/test1/]);
1058 # now $c->req->args is back to what it was before
1061 sub check_message : Private {
1062 my ( $self, $c ) = @_;
1063 my $first_argument = $c->req->args->[0]; # now = 'test1'
1067 As you can see from these examples, you can just use the method name as
1068 long as you are referring to methods in the same controller. If you want
1069 to forward to a method in another controller, or the main application,
1070 you will have to refer to the method by absolute path.
1072 $c->forward('/my/controller/action');
1073 $c->forward('/default'); # calls default in main application
1075 Here are some examples of how to forward to classes and methods.
1077 sub hello : Global {
1078 my ( $self, $c ) = @_;
1079 $c->forward(qw/MyApp::Model::Hello say_hello/);
1083 my ( $self, $c ) = @_;
1084 $c->forward('MyApp::Model::Hello'); # no method: will try 'process'
1087 package MyApp::Model::Hello;
1090 my ( $self, $c ) = @_;
1091 $c->res->body('Hello World!');
1095 my ( $self, $c ) = @_;
1096 $c->res->body('Goodbye World!');
1099 Note that C<forward> returns to the calling action and continues
1100 processing after the action finishes. If you want all further processing
1101 in the calling action to stop, use C<detach> instead, which will execute
1102 the C<detach>ed action and not return to the calling sub. In both cases,
1103 Catalyst will automatically try to call process() if you omit the
1109 Catalyst has a built-in http server for testing or local
1110 deployment. (Later, you can easily use a more powerful server, for
1111 example Apache/mod_perl or FastCGI, in a production environment.)
1113 Start your application on the command line...
1115 script/myapp_server.pl
1117 ...then visit http://localhost:3000/ in a browser to view the output.
1119 You can also do it all from the command line:
1121 script/myapp_test.pl http://localhost/
1123 Catalyst has a number of tools for actual regression testing of
1124 applications. The helper scripts will automatically generate basic tests
1125 that can be extended as you develop your project. To write your own
1126 comprehensive test scripts, L<Test::WWW::Mechanize::Catalyst> is an
1129 For more testing ideas, see L<Catalyst::Manual::Tutorial::Testing>.
1135 =item * L<Catalyst::Manual::About>
1137 =item * L<Catalyst::Manual::Tutorial>
1145 Join #catalyst on irc.perl.org.
1146 Join #catalyst-dev on irc.perl.org to help with development.
1150 http://lists.rawmode.org/mailman/listinfo/catalyst
1151 http://lists.rawmode.org/mailman/listinfo/catalyst-dev
1155 Sebastian Riedel, C<sri@oook.de>
1156 David Naughton, C<naughton@umn.edu>
1157 Marcus Ramberg, C<mramberg@cpan.org>
1158 Jesse Sheidlower, C<jester@panix.com>
1159 Danijel Milicevic, C<me@danijel.de>
1160 Kieren Diment, C<kd@totaldatasolution.com>
1161 Yuval Kogman, C<nothingmuch@woobling.org>
1165 This program is free software. You can redistribute it and/or modify it
1166 under the same terms as Perl itself.