Provided by: libcatalyst-manual-perl_5.9009-2_all bug

NAME

       Catalyst::Manual::Intro - Introduction to Catalyst

DESCRIPTION

       This is a brief introduction to Catalyst. It explains the most important features of how
       Catalyst works and shows how to get a simple application up and running quickly. For an
       introduction (without code) to Catalyst itself, and why you should be using it, see
       Catalyst::Manual::About.  For a systematic step-by-step introduction to writing an
       application with Catalyst, see Catalyst::Manual::Tutorial.

   What is Catalyst?
       Catalyst is an elegant web application framework, extremely flexible yet extremely simple.
       It's similar to Ruby on Rails, Spring (Java), and Maypole, upon which it was originally
       based. Its most important design philosophy is to provide easy access to all the tools you
       need to develop web applications, with few restrictions on how you need to use these
       tools. However, this does mean that it is always possible to do things in a different way.
       Other web frameworks are initially simpler to use, but achieve this by locking the
       programmer into a single set of tools. Catalyst's emphasis on flexibility means that you
       have to think more to use it. We view this as a feature.  For example, this leads to
       Catalyst being better suited to system integration tasks than other web frameworks.

       MVC

       Catalyst follows the Model-View-Controller (MVC) design pattern, allowing you to easily
       separate concerns, like content, presentation, and flow control, into separate modules.
       This separation allows you to modify code that handles one concern without affecting code
       that handles the others. Catalyst promotes the re-use of existing Perl modules that
       already handle common web application concerns well.

       Here's how the Model, View, and Controller map to those concerns, with examples of well-
       known Perl modules you may want to use for each.

       ·   Model

           Access and modify content (data). DBIx::Class, Class::DBI, Xapian, Net::LDAP...

       ·   View

           Present content to the user. Template Toolkit, Mason, HTML::Template...

       ·   Controller

           Control the whole request phase, check parameters, dispatch actions, flow control.
           This is the meat of where Catalyst works.

       If you're unfamiliar with MVC and design patterns, you may want to check out the original
       book on the subject, Design Patterns, by Gamma, Helm, Johnson, and Vlissides, also known
       as the Gang of Four (GoF).  Many, many web application frameworks are based on MVC, which
       is becoming a popular design paradigm for the world wide web.

       Flexibility

       Catalyst is much more flexible than many other frameworks. Rest assured you can use your
       favorite Perl modules with Catalyst.

       ·   Multiple Models, Views, and Controllers

           To build a Catalyst application, you handle each type of concern inside special
           modules called "Components". Often this code will be very simple, just calling out to
           Perl modules like those listed above under "MVC". Catalyst handles these components in
           a very flexible way. Use as many Models, Views, and Controllers as you like, using as
           many different Perl modules as you like, all in the same application. Want to
           manipulate multiple databases, and retrieve some data via LDAP? No problem. Want to
           present data from the same Model using Template Toolkit and PDF::Template? Easy.

       ·   Reuseable Components

           Not only does Catalyst promote the re-use of already existing Perl modules, it also
           allows you to re-use your Catalyst components in multiple Catalyst applications.

       ·   Unrestrained URL-to-Action Dispatching

           Catalyst allows you to dispatch any URLs to any application "Actions", even through
           regular expressions! Unlike most other frameworks, it doesn't require mod_rewrite or
           class and method names in URLs.

           With Catalyst you register your actions and address them directly. For example:

               sub hello : Local {
                   my ( $self, $context ) = @_;
                   $context->response->body('Hello World!');
               }

           Now http://localhost:3000/hello prints "Hello World!".

           Note that actions with the " :Local " attribute are equivalent to using a
           ":Path('action_name') " attribute, so our action could be equivalently:

               sub hi : Path('hello') {
                   my ( $self, $context ) = @_;
                   $context->response->body('Hello World!');
               }

       ·   Support for CGI, mod_perl, Apache::Request, FastCGI

           Use Catalyst::Engine::Apache or Catalyst::Engine::CGI. Another interesting engine is
           Catalyst::Engine::HTTP::Prefork - available from CPAN separately - which will turn the
           built server into a fully fledged production ready server (although you'll probably
           want to run it behind a front end proxy if you end up using it).

       ·   PSGI Support

           Starting with Catalyst version 5.9 Catalyst ships with PSGI integration for even more
           powerful and flexible testing and deployment options.  See Catalyst::PSGI for details.

       Simplicity

       The best part is that Catalyst implements all this flexibility in a very simple way.

       ·   Building Block Interface

           Components interoperate very smoothly. For example, Catalyst automatically makes a
           "Context" object available to every component. Via the context, you can access the
           request object, share data between components, and control the flow of your
           application. Building a Catalyst application feels a lot like snapping together toy
           building blocks, and everything just works.

       ·   Component Auto-Discovery

           No need to "use" all of your components. Catalyst automatically finds and loads them.

       ·   Pre-Built Components for Popular Modules

           See Catalyst::Model::DBIC::Schema for DBIx::Class, or Catalyst::View::TT for Template
           Toolkit.

       ·   Built-in Test Framework

           Catalyst comes with a built-in, lightweight http server and test framework, making it
           easy to test applications from the web browser, and the command line.

       ·   Helper Scripts

           Catalyst provides helper scripts to quickly generate running starter code for
           components and unit tests. Install Catalyst::Devel and see Catalyst::Helper.

   Quickstart
       Here's how to install Catalyst and get a simple application up and running, using the
       helper scripts described above.

       Install

       Installation of Catalyst should be straightforward:

           # perl -MCPAN -e 'install Catalyst::Runtime'
           # perl -MCPAN -e 'install Catalyst::Devel'
           # perl -MCPAN -e 'install Catalyst::View::TT'

       Setup

           $ catalyst.pl MyApp
           # output omitted
           $ cd MyApp
           $ script/myapp_create.pl controller Library::Login

       Frank Speiser's Amazon EC2 Catalyst SDK

       There are currently two flavors of publicly available Amazon Machine Images (AMI) that
       include all the elements you'd need to begin developing in a fully functional Catalyst
       environment within minutes. See Catalyst::Manual::Installation for more details.

       Run

           $ script/myapp_server.pl

       Now visit these locations with your favorite browser or user agent to see Catalyst in
       action:

       (NOTE: Although we create a controller here, we don't actually use it.  Both of these URLs
       should take you to the welcome page.)

       http://localhost:3000/
       http://localhost:3000/library/login/

   How It Works
       Let's see how Catalyst works, by taking a closer look at the components and other parts of
       a Catalyst application.

       Components

       Catalyst has an uncommonly flexible component system. You can define as many "Models",
       "Views", and "Controllers" as you like. As discussed previously, the general idea is that
       the View is responsible for the output of data to the user (typically via a web browser,
       but a View can also generate PDFs or e-mails, for example); the Model is responsible for
       providing data (typically from a relational database); and the Controller is responsible
       for interacting with the user and deciding how user input determines what actions the
       application takes.

       In the world of MVC, there are frequent discussions and disagreements about the nature of
       each element - whether certain types of logic belong in the Model or the Controller, etc.
       Catalyst's flexibility means that this decision is entirely up to you, the programmer;
       Catalyst doesn't enforce anything. See Catalyst::Manual::About for a general discussion of
       these issues.

       Model, View and Controller components must inherit from Catalyst::Model, Catalyst::View
       and Catalyst::Controller, respectively. These, in turn, inherit from Catalyst::Component
       which provides a simple class structure and some common class methods like "config" and
       "new" (constructor).

           package MyApp::Controller::Catalog;
           use Moose;
           use namespace::autoclean;

           BEGIN { extends 'Catalyst::Controller' }

           __PACKAGE__->config( foo => 'bar' );

           1;

       You don't have to "use" or otherwise register Models, Views, and Controllers.  Catalyst
       automatically discovers and instantiates them when you call "setup" in the main
       application. All you need to do is put them in directories named for each Component type.
       You can use a short alias for each one.

       ·   MyApp/Model/

       ·   MyApp/View/

       ·   MyApp/Controller/

       Views

       To show how to define views, we'll use an already-existing base class for the Template
       Toolkit, Catalyst::View::TT. All we need to do is inherit from this class:

           package MyApp::View::TT;

           use strict;
           use base 'Catalyst::View::TT';

           1;

       (You can also generate this automatically by using the helper script:

           script/myapp_create.pl view TT TT

       where the first "TT" tells the script that the name of the view should be "TT", and the
       second that it should be a Template Toolkit view.)

       This gives us a process() method and we can now just do $c->forward('MyApp::View::TT') to
       render our templates. The base class makes process() implicit, so we don't have to say
       "$c->forward(qw/MyApp::View::TT process/)".

           sub hello : Global {
               my ( $self, $c ) = @_;
               $c->stash->{template} = 'hello.tt';
           }

           sub end : Private {
               my ( $self, $c ) = @_;
               $c->forward( $c->view('TT') );
           }

       You normally render templates at the end of a request, so it's a perfect use for the
       global "end" action.

       In practice, however, you would use a default "end" action as supplied by
       Catalyst::Action::RenderView.

       Also, be sure to put the template under the directory specified in "$c->config->{root}",
       or you'll end up looking at the debug screen.

       Models

       Models are providers of data. This data could come from anywhere - a search engine index,
       a spreadsheet, the file system - but typically a Model represents a database table. The
       data source does not intrinsically have much to do with web applications or Catalyst - it
       could just as easily be used to write an offline report generator or a command-line tool.

       To show how to define models, again we'll use an already-existing base class, this time
       for DBIx::Class: Catalyst::Model::DBIC::Schema.  We'll also need
       DBIx::Class::Schema::Loader.

       But first, we need a database.

           -- myapp.sql
           CREATE TABLE foo (
               id INTEGER PRIMARY KEY,
               data TEXT
           );

           CREATE TABLE bar (
               id INTEGER PRIMARY KEY,
               foo INTEGER REFERENCES foo,
               data TEXT
           );

           INSERT INTO foo (data) VALUES ('TEST!');

           % sqlite3 /tmp/myapp.db < myapp.sql

       Now we can create a DBIC::Schema model for this database.

           script/myapp_create.pl model MyModel DBIC::Schema MySchema create=static 'dbi:SQLite:/tmp/myapp.db'

       DBIx::Class::Schema::Loader can automatically load table layouts and relationships, and
       convert them into a static schema definition "MySchema", which you can edit later.

       Use the stash to pass data to your templates.

       We add the following to MyApp/Controller/Root.pm

           sub view : Global {
               my ( $self, $c, $id ) = @_;

               $c->stash->{item} = $c->model('MyModel::Foo')->find($id);
           }

           1;

           sub end : Private {
               my ( $self, $c ) = @_;

               $c->stash->{template} ||= 'index.tt';
               $c->forward( $c->view('TT') );
           }

       We then create a new template file "root/index.tt" containing:

           The Id's data is [% item.data %]

       Models do not have to be part of your Catalyst application; you can always call an outside
       module that serves as your Model:

           # in a Controller
           sub list : Local {
             my ( $self, $c ) = @_;

             $c->stash->{template} = 'list.tt';

             use Some::Outside::Database::Module;
             my @records = Some::Outside::Database::Module->search({
               artist => 'Led Zeppelin',
               });

             $c->stash->{records} = \@records;
           }

       But by using a Model that is part of your Catalyst application, you gain several things:
       you don't have to "use" each component, Catalyst will find and load it automatically at
       compile-time; you can "forward" to the module, which can only be done to Catalyst
       components.  Only Catalyst components can be fetched with "$c->model('SomeModel')".

       Happily, since many people have existing Model classes that they would like to use with
       Catalyst (or, conversely, they want to write Catalyst models that can be used outside of
       Catalyst, e.g.  in a cron job), it's trivial to write a simple component in Catalyst that
       slurps in an outside Model:

           package MyApp::Model::DB;
           use base qw/Catalyst::Model::DBIC::Schema/;
           __PACKAGE__->config(
               schema_class => 'Some::DBIC::Schema',
               connect_info => ['dbi:SQLite:foo.db', '', '', {AutoCommit=>1}]
           );
           1;

       and that's it! Now "Some::DBIC::Schema" is part of your Cat app as "MyApp::Model::DB".

       Within Catalyst, the common approach to writing a model for your application is wrapping a
       generic model (e.g. DBIx::Class::Schema, a bunch of XMLs, or anything really) with an
       object that contains configuration data, convenience methods, and so forth. Thus you will
       in effect have two models - a wrapper model that knows something about Catalyst and your
       web application, and a generic model that is totally independent of these needs.

       Technically, within Catalyst a model is a component - an instance of the model's class
       belonging to the application. It is important to stress that the lifetime of these objects
       is per application, not per request.

       While the model base class (Catalyst::Model) provides things like "config" to better
       integrate the model into the application, sometimes this is not enough, and the model
       requires access to $c itself.

       Situations where this need might arise include:

       ·   Interacting with another model

       ·   Using per-request data to control behavior

       ·   Using plugins from a Model (for example Catalyst::Plugin::Cache).

       From a style perspective it's usually considered bad form to make your model "too smart"
       about things - it should worry about business logic and leave the integration details to
       the controllers. If, however, you find that it does not make sense at all to use an
       auxiliary controller around the model, and the model's need to access $c cannot be
       sidestepped, there exists a power tool called "ACCEPT_CONTEXT".

       Controllers

       Multiple controllers are a good way to separate logical domains of your application.

           package MyApp::Controller::Login;

           use base qw/Catalyst::Controller/;

           sub sign_in : Path("sign-in") { }
           sub new_password : Path("new-password") { }
           sub sign_out : Path("sign-out") { }

           package MyApp::Controller::Catalog;

           use base qw/Catalyst::Controller/;

           sub view : Local { }
           sub list : Local { }

           package MyApp::Controller::Cart;

           use base qw/Catalyst::Controller/;

           sub add : Local { }
           sub update : Local { }
           sub order : Local { }

       Note that you can also supply attributes via the Controller's config so long as you have
       at least one attribute on a subref to be exported (:Action is commonly used for this) -
       for example the following is equivalent to the same controller above:

           package MyApp::Controller::Login;

           use base qw/Catalyst::Controller/;

           __PACKAGE__->config(
             actions => {
               'sign_in' => { Path => 'sign-in' },
               'new_password' => { Path => 'new-password' },
               'sign_out' => { Path => 'sign-out' },
             },
           );

           sub sign_in : Action { }
           sub new_password : Action { }
           sub sign_out : Action { }

       ACCEPT_CONTEXT

       Whenever you call $c->component("Foo") you get back an object - the instance of the model.
       If the component supports the "ACCEPT_CONTEXT" method instead of returning the model
       itself, the return value of "$model->ACCEPT_CONTEXT( $c )" will be used.

       This means that whenever your model/view/controller needs to talk to $c it gets a chance
       to do this when it's needed.

       A typical "ACCEPT_CONTEXT" method will either clone the model and return one with the
       context object set, or it will return a thin wrapper that contains $c and delegates to the
       per-application model object.

       Generally it's a bad idea to expose the context object ($c) in your model or view code.
       Instead you use the "ACCEPT_CONTEXT" subroutine to grab the bits of the context object
       that you need, and provide accessors to them in the model.  This ensures that $c is only
       in scope where it is needed which reduces maintenance and debugging headaches.  So, if for
       example you needed two Catalyst::Model::DBIC::Schema models in the same Catalyst model
       code, you might do something like this:

        __PACKAGE__->mk_accessors(qw(model1_schema model2_schema));
        sub ACCEPT_CONTEXT {
            my ( $self, $c, @extra_arguments ) = @_;
            $self = bless({ %$self,
                    model1_schema  => $c->model('Model1')->schema,
                    model2_schema => $c->model('Model2')->schema
                }, ref($self));
            return $self;
        }

       This effectively treats $self as a prototype object that gets a new parameter.
       @extra_arguments comes from any trailing arguments to "$c->component( $bah,
       @extra_arguments )" (or "$c->model(...)", "$c->view(...)" etc).

       In a subroutine in the  model code, we can then do this:

        sub whatever {
            my ($self) = @_;
            my $schema1 = $self->model1_schema;
            my $schema2 = $self->model2_schema;
            ...
        }

       Note that we still want the Catalyst models to be a thin wrapper around classes that will
       work independently of the Catalyst application to promote reusability of code.  Here we
       might just want to grab the $c->model('DB')->schema so as to get the connection
       information from the Catalyst application's configuration for example.

       The life time of this value is per usage, and not per request. To make this per request
       you can use the following technique:

       Add a field to $c, like "my_model_instance". Then write your "ACCEPT_CONTEXT" method to
       look like this:

           sub ACCEPT_CONTEXT {
             my ( $self, $c ) = @_;

             if ( my $per_request = $c->my_model_instance ) {
               return $per_request;
             } else {
               my $new_instance = bless { %$self, c => $c }, ref($self);
               Scalar::Util::weaken($new_instance->{c}); # or we have a circular reference
               $c->my_model_instance( $new_instance );
               return $new_instance;
             }
           }

       For a similar technique to grab a new component instance on each request, see
       Catalyst::Component::InstancePerContext.

       Application Class

       In addition to the Model, View, and Controller components, there's a single class that
       represents your application itself. This is where you configure your application, load
       plugins, and extend Catalyst.

           package MyApp;

           use strict;
           use parent qw/Catalyst/;
           use Catalyst qw/-Debug ConfigLoader Static::Simple/;
           MyApp->config(
               name => 'My Application',

               # You can put anything else you want in here:
               my_configuration_variable => 'something',
           );
           1;

       In older versions of Catalyst, the application class was where you put global actions.
       However, as of version 5.66, the recommended practice is to place such actions in a
       special Root controller (see "Actions", below), to avoid namespace collisions.

       ·   name

           The name of your application.

       Optionally, you can specify a root parameter for templates and static data.  If omitted,
       Catalyst will try to auto-detect the directory's location. You can define as many
       parameters as you want for plugins or whatever you need. You can access them anywhere in
       your application via "$context->config->{$param_name}".

       Context

       Catalyst automatically blesses a Context object into your application class and makes it
       available everywhere in your application. Use the Context to directly interact with
       Catalyst and glue your "Components" together. For example, if you need to use the Context
       from within a Template Toolkit template, it's already there:

           <h1>Welcome to [% c.config.name %]!</h1>

       As illustrated in our URL-to-Action dispatching example, the Context is always the second
       method parameter, behind the Component object reference or class name itself. Previously
       we called it $context for clarity, but most Catalyst developers just call it $c:

           sub hello : Global {
               my ( $self, $c ) = @_;
               $c->res->body('Hello World!');
           }

       The Context contains several important objects:

       ·   Catalyst::Request

               $c->request
               $c->req # alias

           The request object contains all kinds of request-specific information, like query
           parameters, cookies, uploads, headers, and more.

               $c->req->params->{foo};
               $c->req->cookies->{sessionid};
               $c->req->headers->content_type;
               $c->req->base;
               $c->req->uri_with( { page = $pager->next_page } );

       ·   Catalyst::Response

               $c->response
               $c->res # alias

           The response is like the request, but contains just response-specific information.

               $c->res->body('Hello World');
               $c->res->status(404);
               $c->res->redirect('http://oook.de');

       ·   config

               $c->config
               $c->config->{root};
               $c->config->{name};

       ·   Catalyst::Log

               $c->log
               $c->log->debug('Something happened');
               $c->log->info('Something you should know');

       ·   Stash

               $c->stash
               $c->stash->{foo} = 'bar';
               $c->stash->{baz} = {baz => 'qox'};
               $c->stash->{fred} = [qw/wilma pebbles/];

           and so on.

       The last of these, the stash, is a universal hash for sharing data among application
       components. For an example, we return to our 'hello' action:

           sub hello : Global {
               my ( $self, $c ) = @_;
               $c->stash->{message} = 'Hello World!';
               $c->forward('show_message');
           }

           sub show_message : Private {
               my ( $self, $c ) = @_;
               $c->res->body( $c->stash->{message} );
           }

       Note that the stash should be used only for passing data in an individual request cycle;
       it gets cleared at a new request. If you need to maintain persistent data, use a session.
       See Catalyst::Plugin::Session for a comprehensive set of Catalyst-friendly session-
       handling tools.

       Actions

       You've already seen some examples of actions in this document: subroutines with ":Path"
       and ":Local" attributes attached.  Here, we explain what actions are and how these
       attributes affect what's happening.

       When Catalyst processes a webpage request, it looks for actions to take that will deal
       with the incoming request and produce a response such as a webpage.  You create these
       actions for your application by writing subroutines within your controller and marking
       them with special attributes.  The attributes, the namespace, and the function name
       determine when Catalyst will call the subroutine.

       These action subroutines call certain functions to say what response the webserver will
       give to the web request.  They can also tell Catalyst to run other actions on the request
       (one example of this is called forwarding the request; this is discussed later).

       Action subroutines must have a special attribute on to show that they are actions - as
       well as marking when to call them, this shows that they take a specific set of arguments
       and behave in a specific way.  At startup, Catalyst looks for all the actions in
       controllers, registers them and creates Catalyst::Action objects describing them.  When
       requests come in, Catalyst chooses which actions should be called to handle the request.

       (Occasionally, you might use the action objects directly, but in general, when we talk
       about actions, we're talking about the subroutines in your application that do things to
       process a request.)

       You can choose one of several attributes for action subroutines; these specify which
       requests are processed by that subroutine.  Catalyst will look at the URL it is
       processing, and the actions that it has found, and automatically call the actions it finds
       that match the circumstances of the request.

       The URL (for example "http://localhost:3000/foo/bar") consists of two parts, the base,
       describing how to connect to the server ("http://localhost:3000/" in this example) and the
       path, which the server uses to decide what to return ("foo/bar").  Please note that the
       trailing slash after the hostname[:port] always belongs to base and not to the path.
       Catalyst uses only the path part when trying to find actions to process.

       Depending on the type of action used, the URLs may match a combination of the controller
       namespace, the arguments passed to the action attribute, and the name of the subroutine.

       ·   Controller namespaces

           The namespace is a modified form of the component's class (package) name. This
           modified class name excludes the parts that have a pre-defined meaning in Catalyst
           ("MyApp::Controller" in the above example), replaces "::" with "/", and converts the
           name to lower case.  See "Components" for a full explanation of the pre-defined
           meaning of Catalyst component class names.

       ·   Overriding the namespace

           Note that "__PACKAGE__->config->(namespace => ... )" can be used to override the
           current namespace when matching.  So:

               package MyApp::Controller::Example;

           would normally use 'example' as its namespace for matching, but if this is specially
           overridden with

               __PACKAGE__->config( namespace => 'thing' );

           it matches using the namespace 'thing' instead.

       ·   Application-Wide Actions

           MyApp::Controller::Root, as created by the catalyst.pl script, will typically contain
           actions which are called for the top level of the application (e.g.
           "http://localhost:3000/"):

               package MyApp::Controller::Root;
               use base 'Catalyst::Controller';

               # Sets the actions in this controller to be registered with no prefix
               # so they function identically to actions created in MyApp.pm

               __PACKAGE__->config( namespace => '');

               sub default : Path  {
                   my ( $self, $context ) = @_;
                   $context->response->status(404);
                   $context->response->body('404 not found');
               }

               1;

           The code

               __PACKAGE__->config( namespace => '' );

           makes the controller act as if its namespace is empty.  As you'll see below, an empty
           namespace makes many of the URL-matching attributes, such as :Path and :Local match at
           the start of the URL path (i.e. the application root).

       Action types

       Catalyst supports several types of actions.  These mainly correspond to ways of matching a
       URL to an action subroutine.  Internally, these matching types are implemented by
       Catalyst::DispatchType-derived classes; the documentation there can be helpful in seeing
       how they work.

       They will all attempt to match the start of the path.  The remainder of the path is passed
       as arguments.

       ·   Namespace-prefixed (":Local")

               package MyApp::Controller::My::Controller;
               sub foo : Local { }

           Matches any URL beginning with> "http://localhost:3000/my/controller/foo". The
           namespace and subroutine name together determine the path.

       ·   Root-level (":Global")

               package MyApp::Controller::Foo;

               sub bar : Global {
                   my ($self, $c) = @_;
                   $c->res->body(
                     $c->res->body('sub bar in Controller::Foo triggered on a request for '
                                    . $c->req->uri));
               }

           1;

           Matches "http://localhost:3000/bar" - that is, the action is mapped directly to the
           method name, ignoring the controller namespace.

           ":Global" always matches from the application root: it is simply shorthand for
           ":Path('/methodname')".  ":Local" is shorthand for ":Path('methodname')", which takes
           the controller namespace as described above.

           Usage of the "Global" handler is rare in all but very old Catalyst applications (e.g.
           before Catalyst 5.7).  The use cases where "Global" used to make sense are now largely
           replaced by the "Chained" dispatch type, or by empty "Path" declarations on an
           controller action.  "Global" is still included in Catalyst for backwards
           compatibility, although legitimate use-cases for it may still exist.

       ·   Changing handler behaviour: eating arguments (":Args")

           ":Args" is not an action type per se, but an action modifier - it adds a match
           restriction to any action it's provided to, additionally requiring as many path parts
           as are specified for the action to be matched. For example, in MyApp::Controller::Foo,

             sub bar :Local

           would match any URL starting /foo/bar. To restrict this you can do

             sub bar :Local :Args(1)

           to only match URLs starting /foo/bar/* - with one additional path element required
           after 'bar'.

           NOTE that adding :Args(0) and omitting ":Args" are not the same thing.

           :Args(0) means that no arguments are taken.  Thus, the URL and path must match
           precisely.

           No ":Args" at all means that any number of arguments are taken.  Thus, any URL that
           starts with the controller's path will match. Obviously, this means you cannot chain
           from an action that does not specify args, as the next action in the chain will be
           swallowed as an arg to the first!

       ·   Literal match (":Path")

           "Path" actions match things starting with a precise specified path, and nothing else.

           "Path" actions without a leading forward slash match a specified path relative to
           their current namespace. This example matches URLs starting with
           "http://localhost:3000/my/controller/foo/bar":

               package MyApp::Controller::My::Controller;
               sub bar : Path('foo/bar') { }

           "Path" actions with a leading slash ignore their namespace, and match from the start
           of the URL path. Example:

               package MyApp::Controller::My::Controller;
               sub bar : Path('/foo/bar') { }

           This matches URLs beginning with "http://localhost:3000/foo/bar".

           Empty "Path" definitions match on the namespace only, exactly like ":Global".

               package MyApp::Controller::My::Controller;
               sub bar : Path { }

           The above code matches "http://localhost:3000/my/controller".

           Actions with the ":Local" attribute are similarly equivalent to
           ":Path('action_name')":

               sub foo : Local { }

           is equivalent to

               sub foo : Path('foo') { }

       ·   Pattern match (":Regex" and ":LocalRegex")

           Status: deprecated. Use Chained methods or other techniques.  If you really depend on
           this, install the standalone Catalyst::DispatchType::Regex distribution.

               package MyApp::Controller::My::Controller;
               sub bar : Regex('^item(\d+)/order(\d+)$') { }

           This matches any URL that matches the pattern in the action key, e.g.
           "http://localhost:3000/item23/order42". The '' around the regexp is optional, but
           perltidy likes it. :)

           ":Regex" matches act globally, i.e. without reference to the namespace from which they
           are called.  So the above will not match
           "http://localhost:3000/my/controller/item23/order42" - use a ":LocalRegex" action
           instead.

               package MyApp::Controller::My::Controller;
               sub bar : LocalRegex('^widget(\d+)$') { }

           ":LocalRegex" actions act locally, i.e. the namespace is matched first. The above
           example would match urls like "http://localhost:3000/my/controller/widget23".

           If you omit the ""^"" from either sort of regex, then it will match any depth from the
           base path:

               package MyApp::Controller::Catalog;
               sub bar : LocalRegex('widget(\d+)$') { }

           This differs from the previous example in that it will match
           "http://localhost:3000/my/controller/foo/widget23" - and a number of other paths.

           For both ":LocalRegex" and ":Regex" actions, if you use capturing parentheses to
           extract values within the matching URL, those values are available in the
           "$c->req->captures" array. In the above example, "widget23" would capture "23" in the
           above example, and "$c->req->captures->[0]" would be "23". If you want to pass
           arguments at the end of your URL, you must use regex action keys. See "URL Path
           Handling" below.

       ·   Chained handlers (":Chained")

           Catalyst also provides a method to build and dispatch chains of actions, like

               sub catalog : Chained : CaptureArgs(1) {
                   my ( $self, $c, $arg ) = @_;
                   ...
               }

               sub item : Chained('catalog') : Args(1) {
                   my ( $self, $c, $arg ) = @_;
                   ...
               }

           to handle a "/catalog/*/item/*" path.  Matching actions are called one after another -
           "catalog()" gets called and handed one path element, then "item()" gets called with
           another one.  For further information about this dispatch type, please see
           Catalyst::DispatchType::Chained.

       ·   Private

               sub foo : Private { }

           This will never match a URL - it provides a private action which can be called
           programmatically from within Catalyst, but is never called automatically due to the
           URL being requested.

           Catalyst's ":Private" attribute is exclusive and doesn't work with other attributes
           (so will not work combined with ":Path" or ":Chained" attributes, for instance).

           Private actions can only be executed explicitly from inside a Catalyst application.
           You might do this in your controllers by calling catalyst methods such as "forward" or
           "detach" to fire them:

               $c->forward('foo');
               # or
               $c->detach('foo');

           See "Flow Control" for a full explanation of how you can pass requests on to other
           actions. Note that, as discussed there, when forwarding from another component, you
           must use the absolute path to the method, so that a private "bar" method in your
           "MyApp::Controller::Catalog::Order::Process" controller must, if called from
           elsewhere, be reached with "$c->forward('/catalog/order/process/bar')".

       Note: After seeing these examples, you probably wonder what the point is of defining
       subroutine names for regex and path actions. However, every public action is also a
       private one with a path corresponding to its namespace and subroutine name, so you have
       one unified way of addressing components in your "forward"s.

       Built-in special actions

       If present, the special actions " index ", " auto ", "begin", "end" and " default " are
       called at certain points in the request cycle.

       In response to specific application states, Catalyst will automatically call these built-
       in actions in your application class:

       ·   default : Path

           This is called when no other action matches. It could be used, for example, for
           displaying a generic frontpage for the main app, or an error page for individual
           controllers. Note: in older Catalyst applications you will see "default : Private"
           which is roughly speaking equivalent.

       ·   index : Path : Args (0)

           "index" is much like "default" except that it takes no arguments and it is weighted
           slightly higher in the matching process. It is useful as a static entry point to a
           controller, e.g. to have a static welcome page. Note that it's also weighted higher
           than Path.  Actually the sub name "index" can be called anything you want.  The sub
           attributes are what determines the behaviour of the action.  Note: in older Catalyst
           applications, you will see "index : Private" used, which is roughly speaking
           equivalent.

       ·   begin : Private

           Called at the beginning of a request, once the controller that will run has been
           identified, but before any URL-matching actions are called.  Catalyst will call the
           "begin" function in the controller which contains the action matching the URL.

       ·   end : Private

           Called at the end of a request, after all URL-matching actions are called.  Catalyst
           will call the "end" function in the controller which contains the action matching the
           URL.

       ·   auto : Private

           In addition to the normal built-in actions, you have a special action for making
           chains, "auto". "auto" actions will be run after any "begin", but before your URL-
           matching action is processed. Unlike the other built-ins, multiple "auto" actions can
           be called; they will be called in turn, starting with the application class and going
           through to the most specific class.

       Built-in actions in controllers/autochaining

           package MyApp::Controller::Foo;
           sub begin : Private { }
           sub default : Path  { }
           sub end : Path  { }

       You can define built-in actions within your controllers as well as on your application
       class. In other words, for each of the three built-in actions above, only one will be run
       in any request cycle. Thus, if "MyApp::Controller::Catalog::begin" exists, it will be run
       in place of "MyApp::begin" if you're in the "catalog" namespace, and
       "MyApp::Controller::Catalog::Order::begin" would override this in turn.

           sub auto : Private { }

       "auto", however, doesn't override like this: providing they exist,
       "MyApp::Controller::Root::auto", "MyApp::Controller::Catalog::auto" and
       "MyApp::Catalog::Order::auto" would be called in turn.

       Here are some examples of the order in which the various built-ins would be called:

       for a request for "/foo/foo"
             MyApp::Controller::Foo::auto
             MyApp::Controller::Foo::default # in the absence of MyApp::Controller::Foo::Foo
             MyApp::Controller::Foo::end

       for a request for "/foo/bar/foo"
             MyApp::Controller::Foo::Bar::begin
             MyApp::Controller::Foo::auto
             MyApp::Controller::Foo::Bar::auto
             MyApp::Controller::Foo::Bar::default # for MyApp::Controller::Foo::Bar::foo
             MyApp::Controller::Foo::Bar::end

       The "auto" action is also distinguished by the fact that you can break out of the
       processing chain by returning 0. If an "auto" action returns 0, any remaining actions will
       be skipped, except for "end". So, for the request above, if the first auto returns false,
       the chain would look like this:

       for a request for "/foo/bar/foo" where first "auto" returns false
             MyApp::Controller::Foo::Bar::begin
             MyApp::Controller::Foo::auto # returns false, skips some calls:
             # MyApp::Controller::Foo::Bar::auto - never called
             # MyApp::Controller::Foo::Bar::foo - never called
             MyApp::Controller::Foo::Bar::end

           You can also "die" in the auto action; in that case, the request will go straight to
           the finalize stage, without processing further actions. So in the above example,
           "MyApp::Controller::Foo::Bar::end" is skipped as well.

       An example of why one might use "auto" is an authentication action: you could set up a
       "auto" action to handle authentication in your application class (which will always be
       called first), and if authentication fails, returning 0 would skip any remaining methods
       for that URL.

       Note: Looking at it another way, "auto" actions have to return a true value to continue
       processing!

       URL Path Handling

       You can pass arguments as part of the URL path, separated with forward slashes (/). If the
       action is a Regex or LocalRegex, the '$' anchor must be used. For example, suppose you
       want to handle "/foo/$bar/$baz", where $bar and $baz may vary:

           sub foo : Regex('^foo$') { my ($self, $context, $bar, $baz) = @_; }

       But what if you also defined actions for "/foo/boo" and "/foo/boo/hoo"?

           sub boo : Path('foo/boo') { .. }
           sub hoo : Path('foo/boo/hoo') { .. }

       Catalyst matches actions in most specific to least specific order - that is, whatever
       matches the most pieces of the path wins:

           /foo/boo/hoo
           /foo/boo
           /foo # might be /foo/bar/baz but won't be /foo/boo/hoo

       So Catalyst would never mistakenly dispatch the first two URLs to the '^foo$' action.

       If a Regex or LocalRegex action doesn't use the '$' anchor, the action will still match a
       URL containing arguments; however the arguments won't be available via @_, because the
       Regex will 'eat' them.

       Beware!  If you write two matchers, that match the same path, with the same specificity
       (that is, they match the same quantity of the path), there's no guarantee which will
       actually get called.  Non-regex matchers get tried first, followed by regex ones, but if
       you have, for instance:

          package MyApp::Controller::Root;

          sub match1 :Path('/a/b') { }

          package MyApp::Controller::A;

          sub b :Local { } # Matches /a/b

       then Catalyst will call the one it finds first.  In summary, Don't Do This.

       Query Parameter Processing

       Parameters passed in the URL query string are handled with methods in the
       Catalyst::Request class. The "param" method is functionally equivalent to the "param"
       method of "CGI.pm" and can be used in modules that require this.

           # http://localhost:3000/catalog/view/?category=hardware&page=3
           my $category = $c->req->param('category');
           my $current_page = $c->req->param('page') || 1;

           # multiple values for single parameter name
           my @values = $c->req->param('scrolling_list');

           # DFV requires a CGI.pm-like input hash
           my $results = Data::FormValidator->check($c->req->params, \%dfv_profile);

       Flow Control

       You control the application flow with the "forward" method, which accepts the key of an
       action to execute. This can be an action in the same or another Catalyst controller, or a
       Class name, optionally followed by a method name. After a "forward", the control flow will
       return to the method from which the "forward" was issued.

       A "forward" is similar to a method call. The main differences are that it wraps the call
       in an "eval" to allow exception handling; it automatically passes along the context object
       ($c or $context); and it allows profiling of each call (displayed in the log with
       debugging enabled).

           sub hello : Global {
               my ( $self, $c ) = @_;
               $c->stash->{message} = 'Hello World!';
               $c->forward('check_message'); # $c is automatically included
           }

           sub check_message : Private {
               my ( $self, $c ) = @_;
               return unless $c->stash->{message};
               $c->forward('show_message');
           }

           sub show_message : Private {
               my ( $self, $c ) = @_;
               $c->res->body( $c->stash->{message} );
           }

       A "forward" does not create a new request, so your request object ("$c->req") will remain
       unchanged. This is a key difference between using "forward" and issuing a redirect.

       You can pass new arguments to a "forward" by adding them in an anonymous array. In this
       case "$c->req->args" will be changed for the duration of the "forward" only; upon return,
       the original value of "$c->req->args" will be reset.

           sub hello : Global {
               my ( $self, $c ) = @_;
               $c->stash->{message} = 'Hello World!';
               $c->forward('check_message',[qw/test1/]);
               # now $c->req->args is back to what it was before
           }

           sub check_message : Action {
               my ( $self, $c, $first_argument ) = @_;
               my $also_first_argument = $c->req->args->[0]; # now = 'test1'
               # do something...
           }

       As you can see from these examples, you can just use the method name as long as you are
       referring to methods in the same controller. If you want to forward to a method in another
       controller, or the main application, you will have to refer to the method by absolute
       path.

         $c->forward('/my/controller/action');
         $c->forward('/default'); # calls default in main application

       You can also forward to classes and methods.

           sub hello : Global {
               my ( $self, $c ) = @_;
               $c->forward(qw/MyApp::View:Hello say_hello/);
           }

           sub bye : Global {
               my ( $self, $c ) = @_;
               $c->forward('MyApp::Model::Hello'); # no method: will try 'process'
           }

           package MyApp::View::Hello;

           sub say_hello {
               my ( $self, $c ) = @_;
               $c->res->body('Hello World!');
           }

           sub process {
               my ( $self, $c ) = @_;
               $c->res->body('Goodbye World!');
           }

       This mechanism is used by Catalyst::Action::RenderView to forward to the "process" method
       in a view class.

       It should be noted that whilst forward is useful, it is not the only way of calling other
       code in Catalyst. Forward just gives you stats in the debug screen, wraps the code you're
       calling in an exception handler and localises "$c->request->args".

       If you don't want or need these features then it's perfectly acceptable (and faster) to do
       something like this:

           sub hello : Global {
               my ( $self, $c ) = @_;
               $c->stash->{message} = 'Hello World!';
               $self->check_message( $c, 'test1' );
           }

           sub check_message {
               my ( $self, $c, $first_argument ) = @_;
               # do something...
           }

       Note that "forward" returns to the calling action and continues processing after the
       action finishes. If you want all further processing in the calling action to stop, use
       "detach" instead, which will execute the "detach"ed action and not return to the calling
       sub. In both cases, Catalyst will automatically try to call process() if you omit the
       method.

       Testing

       Catalyst has a built-in http server for testing or local deployment. (Later, you can
       easily use a more powerful server, for example Apache/mod_perl or FastCGI, in a production
       environment.)

       Start your application on the command line...

           script/myapp_server.pl

       ...then visit http://localhost:3000/ in a browser to view the output.

       You can also do it all from the command line:

           script/myapp_test.pl http://localhost/

       Catalyst has a number of tools for actual regression testing of applications. The helper
       scripts will automatically generate basic tests that can be extended as you develop your
       project. To write your own comprehensive test scripts, Test::WWW::Mechanize::Catalyst is
       an invaluable tool.

       For more testing ideas, see Catalyst::Manual::Tutorial::08_Testing.

       Have fun!

SEE ALSO

       ·   Catalyst::Manual::About

       ·   Catalyst::Manual::Tutorial

       ·   Catalyst

SUPPORT

       IRC:

           Join #catalyst on irc.perl.org.
           Join #catalyst-dev on irc.perl.org to help with development.

       Mailing lists:

           http://lists.scsys.co.uk/mailman/listinfo/catalyst
           http://lists.scsys.co.uk/mailman/listinfo/catalyst-dev

       Wiki:

           http://dev.catalystframework.org/wiki

       FAQ:

           http://dev.catalystframework.org/wiki/faq

AUTHORS

       Catalyst Contributors, see Catalyst.pm

COPYRIGHT

       This library is free software. You can redistribute it and/or modify it under the same
       terms as Perl itself.