1Catalyst::Manual::IntroU(s3e)r Contributed Perl DocumentaCtaitoanlyst::Manual::Intro(3)
2
6 Catalyst::Manual::Intro - Introduction to Catalyst
7
9 This is a brief introduction to Catalyst. It explains the most
10 important features of how Catalyst works and shows how to get a simple
11 application up and running quickly. For an introduction (without code)
12 to Catalyst itself, and why you should be using it, see
13 Catalyst::Manual::About. For a systematic step-by-step introduction to
14 writing an application with Catalyst, see Catalyst::Manual::Tutorial.
15 What is Catalyst?
17 Catalyst is an elegant web application framework, extremely flexible
18 yet extremely simple. It's similar to Ruby on Rails, Spring (Java), and
19 Maypole, upon which it was originally based. Its most important design
20 philosophy is to provide easy access to all the tools you need to
21 develop web applications, with few restrictions on how you need to use
22 these tools. However, this does mean that it is always possible to do
23 things in a different way. Other web frameworks are initially simpler
24 to use, but achieve this by locking the programmer into a single set of
25 tools. Catalyst's emphasis on flexibility means that you have to think
26 more to use it. We view this as a feature. For example, this leads to
27 Catalyst being better suited to system integration tasks than other web
28 frameworks.
29 MVC
31 Catalyst follows the Model-View-Controller (MVC) design pattern,
33 allowing you to easily separate concerns, like content, presentation,
34 and flow control, into separate modules. This separation allows you to
35 modify code that handles one concern without affecting code that
36 handles the others. Catalyst promotes the re-use of existing Perl
37 modules that already handle common web application concerns well.
38 Here's how the Model, View, and Controller map to those concerns, with
40 examples of well-known Perl modules you may want to use for each.
41 • Model
43 Access and modify content (data). DBIx::Class, Class::DBI, Xapian,
45 Net::LDAP...
46 • View
48 Present content to the user. Template Toolkit, Mason,
50 HTML::Template...
51 • Controller
53 Control the whole request phase, check parameters, dispatch
55 actions, flow control. This is the meat of where Catalyst works.
56 If you're unfamiliar with MVC and design patterns, you may want to
58 check out the original book on the subject, Design Patterns, by Gamma,
59 Helm, Johnson, and Vlissides, also known as the Gang of Four (GoF).
60 Many, many web application frameworks are based on MVC, which is
61 becoming a popular design paradigm for the world wide web.
62 Flexibility
64 Catalyst is much more flexible than many other frameworks. Rest assured
66 you can use your favorite Perl modules with Catalyst.
67 • Multiple Models, Views, and Controllers
69 To build a Catalyst application, you handle each type of concern
71 inside special modules called "Components". Often this code will be
72 very simple, just calling out to Perl modules like those listed
73 above under "MVC". Catalyst handles these components in a very
74 flexible way. Use as many Models, Views, and Controllers as you
75 like, using as many different Perl modules as you like, all in the
76 same application. Want to manipulate multiple databases, and
77 retrieve some data via LDAP? No problem. Want to present data from
78 the same Model using Template Toolkit and PDF::Template? Easy.
79 • Reuseable Components
81 Not only does Catalyst promote the re-use of already existing Perl
83 modules, it also allows you to re-use your Catalyst components in
84 multiple Catalyst applications.
85 • Unrestrained URL-to-Action Dispatching
87 Catalyst allows you to dispatch any URLs to any application
89 "Actions", even through regular expressions! Unlike most other
90 frameworks, it doesn't require mod_rewrite or class and method
91 names in URLs.
92 With Catalyst you register your actions and address them directly.
94 For example:
95 sub hello : Local {
97 my ( $self, $context ) = @_;
98 $context->response->body('Hello World!');
99 }
100 Now http://localhost:3000/hello prints "Hello World!".
102 Note that actions with the " :Local " attribute are equivalent to
104 using a ":Path('action_name') " attribute, so our action could be
105 equivalently:
106 sub hi : Path('hello') {
108 my ( $self, $context ) = @_;
109 $context->response->body('Hello World!');
110 }
111 • Support for CGI, mod_perl, Apache::Request, FastCGI
113 Use Catalyst::Engine::Apache or Catalyst::Engine::CGI. Another
115 interesting engine is Catalyst::Engine::HTTP::Prefork - available
116 from CPAN separately - which will turn the built server into a
117 fully fledged production ready server (although you'll probably
118 want to run it behind a front end proxy if you end up using it).
119 • PSGI Support
121 Starting with Catalyst version 5.9 Catalyst ships with PSGI
123 integration for even more powerful and flexible testing and
124 deployment options. See Catalyst::PSGI for details.
125 Simplicity
127 The best part is that Catalyst implements all this flexibility in a
129 very simple way.
130 • Building Block Interface
132 Components interoperate very smoothly. For example, Catalyst
134 automatically makes a "Context" object available to every
135 component. Via the context, you can access the request object,
136 share data between components, and control the flow of your
137 application. Building a Catalyst application feels a lot like
138 snapping together toy building blocks, and everything just works.
139 • Component Auto-Discovery
141 No need to "use" all of your components. Catalyst automatically
143 finds and loads them.
144 • Pre-Built Components for Popular Modules
146 See Catalyst::Model::DBIC::Schema for DBIx::Class, or
148 Catalyst::View::TT for Template Toolkit.
149 • Built-in Test Framework
151 Catalyst comes with a built-in, lightweight http server and test
153 framework, making it easy to test applications from the web
154 browser, and the command line.
155 • Helper Scripts
157 Catalyst provides helper scripts to quickly generate running
159 starter code for components and unit tests. Install Catalyst::Devel
160 and see Catalyst::Helper.
161 Quickstart
163 Here's how to install Catalyst and get a simple application up and
164 running, using the helper scripts described above.
165 Install
167 Installation of Catalyst should be straightforward:
169 # perl -MCPAN -e 'install Catalyst::Runtime'
171 # perl -MCPAN -e 'install Catalyst::Devel'
172 # perl -MCPAN -e 'install Catalyst::View::TT'
173 Setup
175 $ catalyst.pl MyApp
177 # output omitted
178 $ cd MyApp
179 $ script/myapp_create.pl controller Library::Login
180 Frank Speiser's Amazon EC2 Catalyst SDK
182 There are currently two flavors of publicly available Amazon Machine
184 Images (AMI) that include all the elements you'd need to begin
185 developing in a fully functional Catalyst environment within minutes.
186 See Catalyst::Manual::Installation for more details.
187 Run
189 $ script/myapp_server.pl
191 Now visit these locations with your favorite browser or user agent to
193 see Catalyst in action:
194 (NOTE: Although we create a controller here, we don't actually use it.
196 Both of these URLs should take you to the welcome page.)
197 http://localhost:3000/
199 http://localhost:3000/library/login/
200 How It Works
202 Let's see how Catalyst works, by taking a closer look at the components
203 and other parts of a Catalyst application.
204 Components
206 Catalyst has an uncommonly flexible component system. You can define as
208 many "Models", "Views", and "Controllers" as you like. As discussed
209 previously, the general idea is that the View is responsible for the
210 output of data to the user (typically via a web browser, but a View can
211 also generate PDFs or e-mails, for example); the Model is responsible
212 for providing data (typically from a relational database); and the
213 Controller is responsible for interacting with the user and deciding
214 how user input determines what actions the application takes.
215 In the world of MVC, there are frequent discussions and disagreements
217 about the nature of each element - whether certain types of logic
218 belong in the Model or the Controller, etc. Catalyst's flexibility
219 means that this decision is entirely up to you, the programmer;
220 Catalyst doesn't enforce anything. See Catalyst::Manual::About for a
221 general discussion of these issues.
222 Model, View and Controller components must inherit from
224 Catalyst::Model, Catalyst::View and Catalyst::Controller, respectively.
225 These, in turn, inherit from Catalyst::Component which provides a
226 simple class structure and some common class methods like "config" and
227 "new" (constructor).
228 package MyApp::Controller::Catalog;
230 use Moose;
231 use namespace::autoclean;
232 BEGIN { extends 'Catalyst::Controller' }
234 __PACKAGE__->config( foo => 'bar' );
236 1;
238 You don't have to "use" or otherwise register Models, Views, and
240 Controllers. Catalyst automatically discovers and instantiates them
241 when you call "setup" in the main application. All you need to do is
242 put them in directories named for each Component type. You can use a
243 short alias for each one.
244 • MyApp/Model/
246 • MyApp/View/
248 • MyApp/Controller/
250 Views
252 To show how to define views, we'll use an already-existing base class
254 for the Template Toolkit, Catalyst::View::TT. All we need to do is
255 inherit from this class:
256 package MyApp::View::TT;
258 use strict;
260 use base 'Catalyst::View::TT';
261 1;
263 (You can also generate this automatically by using the helper script:
265 script/myapp_create.pl view TT TT
267 where the first "TT" tells the script that the name of the view should
269 be "TT", and the second that it should be a Template Toolkit view.)
270 This gives us a process() method and we can now just do
272 "$c->forward('MyApp::View::TT')" to render our templates. The base
273 class makes process() implicit, so we don't have to say
274 "$c->forward(qw/MyApp::View::TT process/)".
275 sub hello : Global {
277 my ( $self, $c ) = @_;
278 $c->stash->{template} = 'hello.tt';
279 }
280 sub end : Private {
282 my ( $self, $c ) = @_;
283 $c->forward( $c->view('TT') );
284 }
285 You normally render templates at the end of a request, so it's a
287 perfect use for the global "end" action.
288 In practice, however, you would use a default "end" action as supplied
290 by Catalyst::Action::RenderView.
291 Also, be sure to put the template under the directory specified in
293 "$c->config->{root}", or you'll end up looking at the debug screen.
294 Models
296 Models are providers of data. This data could come from anywhere - a
298 search engine index, a spreadsheet, the file system - but typically a
299 Model represents a database table. The data source does not
300 intrinsically have much to do with web applications or Catalyst - it
301 could just as easily be used to write an offline report generator or a
302 command-line tool.
303 To show how to define models, again we'll use an already-existing base
305 class, this time for DBIx::Class: Catalyst::Model::DBIC::Schema. We'll
306 also need DBIx::Class::Schema::Loader.
307 But first, we need a database.
309 -- myapp.sql
311 CREATE TABLE foo (
312 id INTEGER PRIMARY KEY,
313 data TEXT
314 );
315 CREATE TABLE bar (
317 id INTEGER PRIMARY KEY,
318 foo INTEGER REFERENCES foo,
319 data TEXT
320 );
321 INSERT INTO foo (data) VALUES ('TEST!');
323 % sqlite3 /tmp/myapp.db < myapp.sql
325 Now we can create a DBIC::Schema model for this database.
327 script/myapp_create.pl model MyModel DBIC::Schema MySchema create=static 'dbi:SQLite:/tmp/myapp.db'
329 DBIx::Class::Schema::Loader can automatically load table layouts and
331 relationships, and convert them into a static schema definition
332 "MySchema", which you can edit later.
333 Use the stash to pass data to your templates.
335 We add the following to MyApp/Controller/Root.pm
337 sub view : Global {
339 my ( $self, $c, $id ) = @_;
340 $c->stash->{item} = $c->model('MyModel::Foo')->find($id);
342 }
343 1;
345 sub end : Private {
347 my ( $self, $c ) = @_;
348 $c->stash->{template} ||= 'index.tt';
350 $c->forward( $c->view('TT') );
351 }
352 We then create a new template file "root/index.tt" containing:
354 The Id's data is [% item.data %]
356 Models do not have to be part of your Catalyst application; you can
358 always call an outside module that serves as your Model:
359 # in a Controller
361 sub list : Local {
362 my ( $self, $c ) = @_;
363 $c->stash->{template} = 'list.tt';
365 use Some::Outside::Database::Module;
367 my @records = Some::Outside::Database::Module->search({
368 artist => 'Led Zeppelin',
369 });
370 $c->stash->{records} = \@records;
372 }
373 But by using a Model that is part of your Catalyst application, you
375 gain several things: you don't have to "use" each component, Catalyst
376 will find and load it automatically at compile-time; you can "forward"
377 to the module, which can only be done to Catalyst components. Only
378 Catalyst components can be fetched with "$c->model('SomeModel')".
379 Happily, since many people have existing Model classes that they would
381 like to use with Catalyst (or, conversely, they want to write Catalyst
382 models that can be used outside of Catalyst, e.g. in a cron job), it's
383 trivial to write a simple component in Catalyst that slurps in an
384 outside Model:
385 package MyApp::Model::DB;
387 use base qw/Catalyst::Model::DBIC::Schema/;
388 __PACKAGE__->config(
389 schema_class => 'Some::DBIC::Schema',
390 connect_info => ['dbi:SQLite:foo.db', '', '', {AutoCommit=>1}]
391 );
392 1;
393 and that's it! Now "Some::DBIC::Schema" is part of your Cat app as
395 "MyApp::Model::DB".
396 Within Catalyst, the common approach to writing a model for your
398 application is wrapping a generic model (e.g. DBIx::Class::Schema, a
399 bunch of XMLs, or anything really) with an object that contains
400 configuration data, convenience methods, and so forth. Thus you will in
401 effect have two models - a wrapper model that knows something about
402 Catalyst and your web application, and a generic model that is totally
403 independent of these needs.
404 Technically, within Catalyst a model is a component - an instance of
406 the model's class belonging to the application. It is important to
407 stress that the lifetime of these objects is per application, not per
408 request.
409 While the model base class (Catalyst::Model) provides things like
411 "config" to better integrate the model into the application, sometimes
412 this is not enough, and the model requires access to $c itself.
413 Situations where this need might arise include:
415 • Interacting with another model
417 • Using per-request data to control behavior
419 • Using plugins from a Model (for example Catalyst::Plugin::Cache).
421 From a style perspective it's usually considered bad form to make your
423 model "too smart" about things - it should worry about business logic
424 and leave the integration details to the controllers. If, however, you
425 find that it does not make sense at all to use an auxiliary controller
426 around the model, and the model's need to access $c cannot be
427 sidestepped, there exists a power tool called "ACCEPT_CONTEXT".
428 Controllers
430 Multiple controllers are a good way to separate logical domains of your
432 application.
433 package MyApp::Controller::Login;
435 use base qw/Catalyst::Controller/;
437 sub sign_in : Path("sign-in") { }
439 sub new_password : Path("new-password") { }
440 sub sign_out : Path("sign-out") { }
441 package MyApp::Controller::Catalog;
443 use base qw/Catalyst::Controller/;
445 sub view : Local { }
447 sub list : Local { }
448 package MyApp::Controller::Cart;
450 use base qw/Catalyst::Controller/;
452 sub add : Local { }
454 sub update : Local { }
455 sub order : Local { }
456 Note that you can also supply attributes via the Controller's config so
458 long as you have at least one attribute on a subref to be exported
459 (:Action is commonly used for this) - for example the following is
460 equivalent to the same controller above:
461 package MyApp::Controller::Login;
463 use base qw/Catalyst::Controller/;
465 __PACKAGE__->config(
467 actions => {
468 'sign_in' => { Path => 'sign-in' },
469 'new_password' => { Path => 'new-password' },
470 'sign_out' => { Path => 'sign-out' },
471 },
472 );
473 sub sign_in : Action { }
475 sub new_password : Action { }
476 sub sign_out : Action { }
477 ACCEPT_CONTEXT
479 Whenever you call "$c->component("Foo")" you get back an object - the
481 instance of the model. If the component supports the "ACCEPT_CONTEXT"
482 method instead of returning the model itself, the return value of
483 "$model->ACCEPT_CONTEXT( $c )" will be used.
484 This means that whenever your model/view/controller needs to talk to $c
486 it gets a chance to do this when it's needed.
487 A typical "ACCEPT_CONTEXT" method will either clone the model and
489 return one with the context object set, or it will return a thin
490 wrapper that contains $c and delegates to the per-application model
491 object.
492 Generally it's a bad idea to expose the context object ($c) in your
494 model or view code. Instead you use the "ACCEPT_CONTEXT" subroutine to
495 grab the bits of the context object that you need, and provide
496 accessors to them in the model. This ensures that $c is only in scope
497 where it is needed which reduces maintenance and debugging headaches.
498 So, if for example you needed two Catalyst::Model::DBIC::Schema models
499 in the same Catalyst model code, you might do something like this:
500 __PACKAGE__->mk_accessors(qw(model1_schema model2_schema));
502 sub ACCEPT_CONTEXT {
503 my ( $self, $c, @extra_arguments ) = @_;
504 $self = bless({ %$self,
505 model1_schema => $c->model('Model1')->schema,
506 model2_schema => $c->model('Model2')->schema
507 }, ref($self));
508 return $self;
509 }
510 This effectively treats $self as a prototype object that gets a new
512 parameter. @extra_arguments comes from any trailing arguments to
513 "$c->component( $bah, @extra_arguments )" (or "$c->model(...)",
514 "$c->view(...)" etc).
515 In a subroutine in the model code, we can then do this:
517 sub whatever {
519 my ($self) = @_;
520 my $schema1 = $self->model1_schema;
521 my $schema2 = $self->model2_schema;
522 ...
523 }
524 Note that we still want the Catalyst models to be a thin wrapper around
526 classes that will work independently of the Catalyst application to
527 promote reusability of code. Here we might just want to grab the
528 "$c->model('DB')->schema" so as to get the connection information from
529 the Catalyst application's configuration for example.
530 The life time of this value is per usage, and not per request. To make
532 this per request you can use the following technique:
533 Add a field to $c, like "my_model_instance". Then write your
535 "ACCEPT_CONTEXT" method to look like this:
536 sub ACCEPT_CONTEXT {
538 my ( $self, $c ) = @_;
539 if ( my $per_request = $c->my_model_instance ) {
541 return $per_request;
542 } else {
543 my $new_instance = bless { %$self, c => $c }, ref($self);
544 Scalar::Util::weaken($new_instance->{c}); # or we have a circular reference
545 $c->my_model_instance( $new_instance );
546 return $new_instance;
547 }
548 }
549 For a similar technique to grab a new component instance on each
551 request, see Catalyst::Component::InstancePerContext.
552 Application Class
554 In addition to the Model, View, and Controller components, there's a
556 single class that represents your application itself. This is where you
557 configure your application, load plugins, and extend Catalyst.
558 package MyApp;
560 use strict;
562 use parent qw/Catalyst/;
563 use Catalyst qw/-Debug ConfigLoader Static::Simple/;
564 MyApp->config(
565 name => 'My Application',
566 # You can put anything else you want in here:
568 my_configuration_variable => 'something',
569 );
570 1;
571 In older versions of Catalyst, the application class was where you put
573 global actions. However, as of version 5.66, the recommended practice
574 is to place such actions in a special Root controller (see "Actions",
575 below), to avoid namespace collisions.
576 • name
578 The name of your application.
580 Optionally, you can specify a root parameter for templates and static
582 data. If omitted, Catalyst will try to auto-detect the directory's
583 location. You can define as many parameters as you want for plugins or
584 whatever you need. You can access them anywhere in your application via
585 "$context->config->{$param_name}".
586 Context
588 Catalyst automatically blesses a Context object into your application
590 class and makes it available everywhere in your application. Use the
591 Context to directly interact with Catalyst and glue your "Components"
592 together. For example, if you need to use the Context from within a
593 Template Toolkit template, it's already there:
594 <h1>Welcome to [% c.config.name %]!</h1>
596 As illustrated in our URL-to-Action dispatching example, the Context is
598 always the second method parameter, behind the Component object
599 reference or class name itself. Previously we called it $context for
600 clarity, but most Catalyst developers just call it $c:
601 sub hello : Global {
603 my ( $self, $c ) = @_;
604 $c->res->body('Hello World!');
605 }
606 The Context contains several important objects:
608 • Catalyst::Request
610 $c->request
612 $c->req # alias
613 The request object contains all kinds of request-specific
615 information, like query parameters, cookies, uploads, headers, and
616 more.
617 $c->req->params->{foo};
619 $c->req->cookies->{sessionid};
620 $c->req->headers->content_type;
621 $c->req->base;
622 $c->req->uri_with( { page = $pager->next_page } );
623 • Catalyst::Response
625 $c->response
627 $c->res # alias
628 The response is like the request, but contains just response-
630 specific information.
631 $c->res->body('Hello World');
633 $c->res->status(404);
634 $c->res->redirect('http://oook.de');
635 • config
637 $c->config
639 $c->config->{root};
640 $c->config->{name};
641 • Catalyst::Log
643 $c->log
645 $c->log->debug('Something happened');
646 $c->log->info('Something you should know');
647 • Stash
649 $c->stash
651 $c->stash->{foo} = 'bar';
652 $c->stash->{baz} = {baz => 'qox'};
653 $c->stash->{fred} = [qw/wilma pebbles/];
654 and so on.
656 The last of these, the stash, is a universal hash for sharing data
658 among application components. For an example, we return to our 'hello'
659 action:
660 sub hello : Global {
662 my ( $self, $c ) = @_;
663 $c->stash->{message} = 'Hello World!';
664 $c->forward('show_message');
665 }
666 sub show_message : Private {
668 my ( $self, $c ) = @_;
669 $c->res->body( $c->stash->{message} );
670 }
671 Note that the stash should be used only for passing data in an
673 individual request cycle; it gets cleared at a new request. If you need
674 to maintain persistent data, use a session. See
675 Catalyst::Plugin::Session for a comprehensive set of Catalyst-friendly
676 session-handling tools.
677 Actions
679 You've already seen some examples of actions in this document:
681 subroutines with ":Path" and ":Local" attributes attached. Here, we
682 explain what actions are and how these attributes affect what's
683 happening.
684 When Catalyst processes a webpage request, it looks for actions to take
686 that will deal with the incoming request and produce a response such as
687 a webpage. You create these actions for your application by writing
688 subroutines within your controller and marking them with special
689 attributes. The attributes, the namespace, and the function name
690 determine when Catalyst will call the subroutine.
691 These action subroutines call certain functions to say what response
693 the webserver will give to the web request. They can also tell
694 Catalyst to run other actions on the request (one example of this is
695 called forwarding the request; this is discussed later).
696 Action subroutines must have a special attribute on to show that they
698 are actions - as well as marking when to call them, this shows that
699 they take a specific set of arguments and behave in a specific way. At
700 startup, Catalyst looks for all the actions in controllers, registers
701 them and creates Catalyst::Action objects describing them. When
702 requests come in, Catalyst chooses which actions should be called to
703 handle the request.
704 (Occasionally, you might use the action objects directly, but in
706 general, when we talk about actions, we're talking about the
707 subroutines in your application that do things to process a request.)
708 You can choose one of several attributes for action subroutines; these
710 specify which requests are processed by that subroutine. Catalyst will
711 look at the URL it is processing, and the actions that it has found,
712 and automatically call the actions it finds that match the
713 circumstances of the request.
714 The URL (for example "http://localhost:3000/foo/bar") consists of two
716 parts, the base, describing how to connect to the server
717 ("http://localhost:3000/" in this example) and the path, which the
718 server uses to decide what to return ("foo/bar"). Please note that the
719 trailing slash after the hostname[:port] always belongs to base and not
720 to the path. Catalyst uses only the path part when trying to find
721 actions to process.
722 Depending on the type of action used, the URLs may match a combination
724 of the controller namespace, the arguments passed to the action
725 attribute, and the name of the subroutine.
726 • Controller namespaces
728 The namespace is a modified form of the component's class (package)
730 name. This modified class name excludes the parts that have a pre-
731 defined meaning in Catalyst ("MyApp::Controller" in the above
732 example), replaces "::" with "/", and converts the name to lower
733 case. See "Components" for a full explanation of the pre-defined
734 meaning of Catalyst component class names.
735 • Overriding the namespace
737 Note that "__PACKAGE__->config->(namespace => ... )" can be used to
739 override the current namespace when matching. So:
740 package MyApp::Controller::Example;
742 would normally use 'example' as its namespace for matching, but if
744 this is specially overridden with
745 __PACKAGE__->config( namespace => 'thing' );
747 it matches using the namespace 'thing' instead.
749 • Application-Wide Actions
751 MyApp::Controller::Root, as created by the catalyst.pl script, will
753 typically contain actions which are called for the top level of the
754 application (e.g. "http://localhost:3000/"):
755 package MyApp::Controller::Root;
757 use base 'Catalyst::Controller';
758 # Sets the actions in this controller to be registered with no prefix
760 # so they function identically to actions created in MyApp.pm
761 __PACKAGE__->config( namespace => '');
763 sub default : Path {
765 my ( $self, $context ) = @_;
766 $context->response->status(404);
767 $context->response->body('404 not found');
768 }
769 1;
771 The code
773 __PACKAGE__->config( namespace => '' );
775 makes the controller act as if its namespace is empty. As you'll
777 see below, an empty namespace makes many of the URL-matching
778 attributes, such as :Path and :Local match at the start of the URL
779 path (i.e. the application root).
780 Action types
782 Catalyst supports several types of actions. These mainly correspond to
784 ways of matching a URL to an action subroutine. Internally, these
785 matching types are implemented by Catalyst::DispatchType-derived
786 classes; the documentation there can be helpful in seeing how they
787 work.
788 They will all attempt to match the start of the path. The remainder of
790 the path is passed as arguments.
791 • Namespace-prefixed (":Local")
793 package MyApp::Controller::My::Controller;
795 sub foo : Local { }
796 Matches any URL beginning with>
798 "http://localhost:3000/my/controller/foo". The namespace and
799 subroutine name together determine the path.
800 • Root-level (":Global")
802 package MyApp::Controller::Foo;
804 sub bar : Global {
806 my ($self, $c) = @_;
807 $c->res->body(
808 $c->res->body('sub bar in Controller::Foo triggered on a request for '
809 . $c->req->uri));
810 }
811 1;
813 Matches "http://localhost:3000/bar" - that is, the action is mapped
815 directly to the method name, ignoring the controller namespace.
816 ":Global" always matches from the application root: it is simply
818 shorthand for ":Path('/methodname')". ":Local" is shorthand for
819 ":Path('methodname')", which takes the controller namespace as
820 described above.
821 Usage of the "Global" handler is rare in all but very old Catalyst
823 applications (e.g. before Catalyst 5.7). The use cases where
824 "Global" used to make sense are now largely replaced by the
825 "Chained" dispatch type, or by empty "Path" declarations on an
826 controller action. "Global" is still included in Catalyst for
827 backwards compatibility, although legitimate use-cases for it may
828 still exist.
829 • Changing handler behaviour: eating arguments (":Args")
831 ":Args" is not an action type per se, but an action modifier - it
833 adds a match restriction to any action it's provided to,
834 additionally requiring as many path parts as are specified for the
835 action to be matched. For example, in MyApp::Controller::Foo,
836 sub bar :Local
838 would match any URL starting /foo/bar. To restrict this you can do
840 sub bar :Local :Args(1)
842 to only match URLs starting /foo/bar/* - with one additional path
844 element required after 'bar'.
845 NOTE that adding :Args(0) and omitting ":Args" are not the same
847 thing.
848 :Args(0) means that no arguments are taken. Thus, the URL and path
850 must match precisely.
851 No ":Args" at all means that any number of arguments are taken.
853 Thus, any URL that starts with the controller's path will match.
854 Obviously, this means you cannot chain from an action that does not
855 specify args, as the next action in the chain will be swallowed as
856 an arg to the first!
857 • Literal match (":Path")
859 "Path" actions match things starting with a precise specified path,
861 and nothing else.
862 "Path" actions without a leading forward slash match a specified
864 path relative to their current namespace. This example matches URLs
865 starting with "http://localhost:3000/my/controller/foo/bar":
866 package MyApp::Controller::My::Controller;
868 sub bar : Path('foo/bar') { }
869 "Path" actions with a leading slash ignore their namespace, and
871 match from the start of the URL path. Example:
872 package MyApp::Controller::My::Controller;
874 sub bar : Path('/foo/bar') { }
875 This matches URLs beginning with "http://localhost:3000/foo/bar".
877 Empty "Path" definitions match on the namespace only, exactly like
879 ":Global".
880 package MyApp::Controller::My::Controller;
882 sub bar : Path { }
883 The above code matches "http://localhost:3000/my/controller".
885 Actions with the ":Local" attribute are similarly equivalent to
887 ":Path('action_name')":
888 sub foo : Local { }
890 is equivalent to
892 sub foo : Path('foo') { }
894 • Pattern match (":Regex" and ":LocalRegex")
896 Status: deprecated. Use Chained methods or other techniques. If
898 you really depend on this, install the standalone
899 Catalyst::DispatchType::Regex distribution.
900 package MyApp::Controller::My::Controller;
902 sub bar : Regex('^item(\d+)/order(\d+)$') { }
903 This matches any URL that matches the pattern in the action key,
905 e.g. "http://localhost:3000/item23/order42". The '' around the
906 regexp is optional, but perltidy likes it. :)
907 ":Regex" matches act globally, i.e. without reference to the
909 namespace from which they are called. So the above will not match
910 "http://localhost:3000/my/controller/item23/order42" - use a
911 ":LocalRegex" action instead.
912 package MyApp::Controller::My::Controller;
914 sub bar : LocalRegex('^widget(\d+)$') { }
915 ":LocalRegex" actions act locally, i.e. the namespace is matched
917 first. The above example would match urls like
918 "http://localhost:3000/my/controller/widget23".
919 If you omit the ""^"" from either sort of regex, then it will match
921 any depth from the base path:
922 package MyApp::Controller::Catalog;
924 sub bar : LocalRegex('widget(\d+)$') { }
925 This differs from the previous example in that it will match
927 "http://localhost:3000/my/controller/foo/widget23" - and a number
928 of other paths.
929 For both ":LocalRegex" and ":Regex" actions, if you use capturing
931 parentheses to extract values within the matching URL, those values
932 are available in the "$c->req->captures" array. In the above
933 example, "widget23" would capture "23" in the above example, and
934 "$c->req->captures->[0]" would be "23". If you want to pass
935 arguments at the end of your URL, you must use regex action keys.
936 See "URL Path Handling" below.
937 • Chained handlers (":Chained")
939 Catalyst also provides a method to build and dispatch chains of
941 actions, like
942 sub catalog : Chained : CaptureArgs(1) {
944 my ( $self, $c, $arg ) = @_;
945 ...
946 }
947 sub item : Chained('catalog') : Args(1) {
949 my ( $self, $c, $arg ) = @_;
950 ...
951 }
952 to handle a "/catalog/*/item/*" path. Matching actions are called
954 one after another - "catalog()" gets called and handed one path
955 element, then "item()" gets called with another one. For further
956 information about this dispatch type, please see
957 Catalyst::DispatchType::Chained.
958 • Private
960 sub foo : Private { }
962 This will never match a URL - it provides a private action which
964 can be called programmatically from within Catalyst, but is never
965 called automatically due to the URL being requested.
966 Catalyst's ":Private" attribute is exclusive and doesn't work with
968 other attributes (so will not work combined with ":Path" or
969 ":Chained" attributes, for instance).
970 Private actions can only be executed explicitly from inside a
972 Catalyst application. You might do this in your controllers by
973 calling catalyst methods such as "forward" or "detach" to fire
974 them:
975 $c->forward('foo');
977 # or
978 $c->detach('foo');
979 See "Flow Control" for a full explanation of how you can pass
981 requests on to other actions. Note that, as discussed there, when
982 forwarding from another component, you must use the absolute path
983 to the method, so that a private "bar" method in your
984 "MyApp::Controller::Catalog::Order::Process" controller must, if
985 called from elsewhere, be reached with
986 "$c->forward('/catalog/order/process/bar')".
987 Note: After seeing these examples, you probably wonder what the point
989 is of defining subroutine names for regex and path actions. However,
990 every public action is also a private one with a path corresponding to
991 its namespace and subroutine name, so you have one unified way of
992 addressing components in your "forward"s.
993 Built-in special actions
995 If present, the special actions " index ", " auto ", "begin", "end" and
997 " default " are called at certain points in the request cycle.
998 In response to specific application states, Catalyst will automatically
1000 call these built-in actions in your application class:
1001 • default : Path
1003 This is called when no other action matches. It could be used, for
1005 example, for displaying a generic frontpage for the main app, or an
1006 error page for individual controllers. Note: in older Catalyst
1007 applications you will see "default : Private" which is roughly
1008 speaking equivalent.
1009 • index : Path : Args (0)
1011 "index" is much like "default" except that it takes no arguments
1013 and it is weighted slightly higher in the matching process. It is
1014 useful as a static entry point to a controller, e.g. to have a
1015 static welcome page. Note that it's also weighted higher than Path.
1016 Actually the sub name "index" can be called anything you want. The
1017 sub attributes are what determines the behaviour of the action.
1018 Note: in older Catalyst applications, you will see "index :
1019 Private" used, which is roughly speaking equivalent.
1020 • begin : Private
1022 Called at the beginning of a request, once the controller that will
1024 run has been identified, but before any URL-matching actions are
1025 called. Catalyst will call the "begin" function in the controller
1026 which contains the action matching the URL.
1027 • end : Private
1029 Called at the end of a request, after all URL-matching actions are
1031 called. Catalyst will call the "end" function in the controller
1032 which contains the action matching the URL.
1033 • auto : Private
1035 In addition to the normal built-in actions, you have a special
1037 action for making chains, "auto". "auto" actions will be run after
1038 any "begin", but before your URL-matching action is processed.
1039 Unlike the other built-ins, multiple "auto" actions can be called;
1040 they will be called in turn, starting with the application class
1041 and going through to the most specific class.
1042 Built-in actions in controllers/autochaining
1044 package MyApp::Controller::Foo;
1046 sub begin : Private { }
1047 sub default : Path { }
1048 sub end : Path { }
1049 You can define built-in actions within your controllers as well as on
1051 your application class. In other words, for each of the three built-in
1052 actions above, only one will be run in any request cycle. Thus, if
1053 "MyApp::Controller::Catalog::begin" exists, it will be run in place of
1054 "MyApp::begin" if you're in the "catalog" namespace, and
1055 "MyApp::Controller::Catalog::Order::begin" would override this in turn.
1056 sub auto : Private { }
1058 "auto", however, doesn't override like this: providing they exist,
1060 "MyApp::Controller::Root::auto", "MyApp::Controller::Catalog::auto" and
1061 "MyApp::Catalog::Order::auto" would be called in turn.
1062 Here are some examples of the order in which the various built-ins
1064 would be called:
1065 for a request for "/foo/foo"
1067 MyApp::Controller::Foo::auto
1068 MyApp::Controller::Foo::default # in the absence of MyApp::Controller::Foo::Foo
1069 MyApp::Controller::Foo::end
1070 for a request for "/foo/bar/foo"
1072 MyApp::Controller::Foo::Bar::begin
1073 MyApp::Controller::Foo::auto
1074 MyApp::Controller::Foo::Bar::auto
1075 MyApp::Controller::Foo::Bar::default # for MyApp::Controller::Foo::Bar::foo
1076 MyApp::Controller::Foo::Bar::end
1077 The "auto" action is also distinguished by the fact that you can break
1079 out of the processing chain by returning 0. If an "auto" action returns
1080 0, any remaining actions will be skipped, except for "end". So, for the
1081 request above, if the first auto returns false, the chain would look
1082 like this:
1083 for a request for "/foo/bar/foo" where first "auto" returns false
1085 MyApp::Controller::Foo::Bar::begin
1086 MyApp::Controller::Foo::auto # returns false, skips some calls:
1087 # MyApp::Controller::Foo::Bar::auto - never called
1088 # MyApp::Controller::Foo::Bar::foo - never called
1089 MyApp::Controller::Foo::Bar::end
1090 You can also "die" in the auto action; in that case, the request
1092 will go straight to the finalize stage, without processing further
1093 actions. So in the above example,
1094 "MyApp::Controller::Foo::Bar::end" is skipped as well.
1095 An example of why one might use "auto" is an authentication action: you
1097 could set up a "auto" action to handle authentication in your
1098 application class (which will always be called first), and if
1099 authentication fails, returning 0 would skip any remaining methods for
1100 that URL.
1101 Note: Looking at it another way, "auto" actions have to return a true
1103 value to continue processing!
1104 URL Path Handling
1106 You can pass arguments as part of the URL path, separated with forward
1108 slashes (/). If the action is a Regex or LocalRegex, the '$' anchor
1109 must be used. For example, suppose you want to handle "/foo/$bar/$baz",
1110 where $bar and $baz may vary:
1111 sub foo : Regex('^foo$') { my ($self, $context, $bar, $baz) = @_; }
1113 But what if you also defined actions for "/foo/boo" and "/foo/boo/hoo"?
1115 sub boo : Path('foo/boo') { .. }
1117 sub hoo : Path('foo/boo/hoo') { .. }
1118 Catalyst matches actions in most specific to least specific order -
1120 that is, whatever matches the most pieces of the path wins:
1121 /foo/boo/hoo
1123 /foo/boo
1124 /foo # might be /foo/bar/baz but won't be /foo/boo/hoo
1125 So Catalyst would never mistakenly dispatch the first two URLs to the
1127 '^foo$' action.
1128 If a Regex or LocalRegex action doesn't use the '$' anchor, the action
1130 will still match a URL containing arguments; however the arguments
1131 won't be available via @_, because the Regex will 'eat' them.
1132 Beware! If you write two matchers, that match the same path, with the
1134 same specificity (that is, they match the same quantity of the path),
1135 there's no guarantee which will actually get called. Non-regex
1136 matchers get tried first, followed by regex ones, but if you have, for
1137 instance:
1138 package MyApp::Controller::Root;
1140 sub match1 :Path('/a/b') { }
1142 package MyApp::Controller::A;
1144 sub b :Local { } # Matches /a/b
1146 then Catalyst will call the one it finds first. In summary, Don't Do
1148 This.
1149 Query Parameter Processing
1151 Parameters passed in the URL query string are handled with methods in
1153 the Catalyst::Request class. The "param" method is functionally
1154 equivalent to the "param" method of CGI.pm and can be used in modules
1155 that require this.
1156 # http://localhost:3000/catalog/view/?category=hardware&page=3
1158 my $category = $c->req->param('category');
1159 my $current_page = $c->req->param('page') || 1;
1160 # multiple values for single parameter name
1162 my @values = $c->req->param('scrolling_list');
1163 # DFV requires a CGI.pm-like input hash
1165 my $results = Data::FormValidator->check($c->req->params, \%dfv_profile);
1166 Flow Control
1168 You control the application flow with the "forward" method, which
1170 accepts the key of an action to execute. This can be an action in the
1171 same or another Catalyst controller, or a Class name, optionally
1172 followed by a method name. After a "forward", the control flow will
1173 return to the method from which the "forward" was issued.
1174 A "forward" is similar to a method call. The main differences are that
1176 it wraps the call in an "eval" to allow exception handling; it
1177 automatically passes along the context object ($c or $context); and it
1178 allows profiling of each call (displayed in the log with debugging
1179 enabled).
1180 sub hello : Global {
1182 my ( $self, $c ) = @_;
1183 $c->stash->{message} = 'Hello World!';
1184 $c->forward('check_message'); # $c is automatically included
1185 }
1186 sub check_message : Private {
1188 my ( $self, $c ) = @_;
1189 return unless $c->stash->{message};
1190 $c->forward('show_message');
1191 }
1192 sub show_message : Private {
1194 my ( $self, $c ) = @_;
1195 $c->res->body( $c->stash->{message} );
1196 }
1197 A "forward" does not create a new request, so your request object
1199 ("$c->req") will remain unchanged. This is a key difference between
1200 using "forward" and issuing a redirect.
1201 You can pass new arguments to a "forward" by adding them in an
1203 anonymous array. In this case "$c->req->args" will be changed for the
1204 duration of the "forward" only; upon return, the original value of
1205 "$c->req->args" will be reset.
1206 sub hello : Global {
1208 my ( $self, $c ) = @_;
1209 $c->stash->{message} = 'Hello World!';
1210 $c->forward('check_message',[qw/test1/]);
1211 # now $c->req->args is back to what it was before
1212 }
1213 sub check_message : Action {
1215 my ( $self, $c, $first_argument ) = @_;
1216 my $also_first_argument = $c->req->args->[0]; # now = 'test1'
1217 # do something...
1218 }
1219 As you can see from these examples, you can just use the method name as
1221 long as you are referring to methods in the same controller. If you
1222 want to forward to a method in another controller, or the main
1223 application, you will have to refer to the method by absolute path.
1224 $c->forward('/my/controller/action');
1226 $c->forward('/default'); # calls default in main application
1227 You can also forward to classes and methods.
1229 sub hello : Global {
1231 my ( $self, $c ) = @_;
1232 $c->forward(qw/MyApp::View:Hello say_hello/);
1233 }
1234 sub bye : Global {
1236 my ( $self, $c ) = @_;
1237 $c->forward('MyApp::Model::Hello'); # no method: will try 'process'
1238 }
1239 package MyApp::View::Hello;
1241 sub say_hello {
1243 my ( $self, $c ) = @_;
1244 $c->res->body('Hello World!');
1245 }
1246 sub process {
1248 my ( $self, $c ) = @_;
1249 $c->res->body('Goodbye World!');
1250 }
1251 This mechanism is used by Catalyst::Action::RenderView to forward to
1253 the "process" method in a view class.
1254 It should be noted that whilst forward is useful, it is not the only
1256 way of calling other code in Catalyst. Forward just gives you stats in
1257 the debug screen, wraps the code you're calling in an exception handler
1258 and localises "$c->request->args".
1259 If you don't want or need these features then it's perfectly acceptable
1261 (and faster) to do something like this:
1262 sub hello : Global {
1264 my ( $self, $c ) = @_;
1265 $c->stash->{message} = 'Hello World!';
1266 $self->check_message( $c, 'test1' );
1267 }
1268 sub check_message {
1270 my ( $self, $c, $first_argument ) = @_;
1271 # do something...
1272 }
1273 Note that "forward" returns to the calling action and continues
1275 processing after the action finishes. If you want all further
1276 processing in the calling action to stop, use "detach" instead, which
1277 will execute the "detach"ed action and not return to the calling sub.
1278 In both cases, Catalyst will automatically try to call process() if you
1279 omit the method.
1280 Testing
1282 Catalyst has a built-in http server for testing or local deployment.
1284 (Later, you can easily use a more powerful server, for example
1285 Apache/mod_perl or FastCGI, in a production environment.)
1286 Start your application on the command line...
1288 script/myapp_server.pl
1290 ...then visit http://localhost:3000/ in a browser to view the output.
1292 You can also do it all from the command line:
1294 script/myapp_test.pl http://localhost/
1296 Catalyst has a number of tools for actual regression testing of
1298 applications. The helper scripts will automatically generate basic
1299 tests that can be extended as you develop your project. To write your
1300 own comprehensive test scripts, Test::WWW::Mechanize::Catalyst is an
1301 invaluable tool.
1302 For more testing ideas, see Catalyst::Manual::Tutorial::08_Testing.
1304 Have fun!
1306
1308 • Catalyst::Manual::About
1309 • Catalyst::Manual::Tutorial
1311 • Catalyst
1313
1315 IRC:
1316 Join #catalyst on irc.perl.org.
1318 Join #catalyst-dev on irc.perl.org to help with development.
1319 Mailing lists:
1321 http://lists.scsys.co.uk/mailman/listinfo/catalyst
1323 http://lists.scsys.co.uk/mailman/listinfo/catalyst-dev
1324 Wiki:
1326 http://dev.catalystframework.org/wiki
1328 FAQ:
1330 http://dev.catalystframework.org/wiki/faq
1332
1334 Catalyst Contributors, see Catalyst.pm
1335
1337 This library is free software. You can redistribute it and/or modify it
1338 under the same terms as Perl itself.
1339perl v5.36.0 2022-07-22 Catalyst::Manual::Intro(3)