Provided by: libcatalyst-manual-perl_5.9007-1_all 
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 philosphy 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'
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/M/
• MyApp/View/
• MyApp/V/
• MyApp/Controller/
• MyApp/C/
In older versions of Catalyst, the recommended practice (and the one automatically created by helper
scripts) was to name the directories "M/", "V/", and "C/". Though these still work, they are deprecated
and we now recommend the use of the full names.
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 auxillary 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 login : Path("login") { }
sub new_password : Path("new-password") { }
sub logout : Path("logout") { }
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 neaded 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 shorthandfor ":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 missing out :Args completely 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 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 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")
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::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.
perl v5.14.2 2013-05-06 Catalyst::Manual::Intro(3pm)