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Catalyst::Manual::TutoUser:ConCatalyst::Manual::Tutorial::02_CatalystBasics(3)

NAME
       Catalyst::Manual::Tutorial::02_CatalystBasics - Catalyst Tutorial -
       Chapter 2: Catalyst Application Development Basics

OVERVIEW
       This is Chapter 2 of 10 for the Catalyst tutorial.

       Tutorial Overview

       1.  Introduction

       2.  02_Catalyst Basics

       3.  More Catalyst Basics

       4.  Basic CRUD

       5.  Authentication

       6.  Authorization

       7.  Debugging

       8.  Testing

       9.  Advanced CRUD

       10. Appendices

DESCRIPTION
       In this chapter of the tutorial, we will create a very basic Catalyst
       web application, demonstrating a number of powerful capabilities, such
       as:

       ·   Helper Scripts

	   Catalyst helper scripts that can be used to rapidly bootstrap the
	   skeletal structure of an application.

       ·   MVC

	   Model/View/Controller (MVC) provides an architecture that
	   facilitates a clean "separation of control" between the different
	   portions of your application. Given that many other documents cover
	   this subject in detail, MVC will not be discussed in depth here
	   (for an excellent introduction to MVC and general Catalyst
	   concepts, please see Catalyst::Manual::About). In short:

	   ·   Model

	       The model usually represents a data store. In most
	       applications, the model equates to the objects that are created
	       from and saved to your SQL database.

	   ·   View

	       The view takes model objects and renders them into something
	       for the end user to look at. Normally this involves a template-
	       generation tool that creates HTML for the user's web browser,
	       but it could easily be code that generates other forms such as
	       PDF documents, e-mails, spreadsheets, or even "behind the
	       scenes" formats such as XML and JSON.

	   ·   Controller

	       As suggested by its name, the controller takes user requests
	       and routes them to the necessary model and view.

       ·   ORM

	   The use of Object-Relational Mapping (ORM) technology for database
	   access. Specifically, ORM provides an automated and standardized
	   means to persist and restore objects to/from a relational database
	   and will automatically create our Catalyst model for use with a
	   database.

       You can checkout the source code for this example from the catalyst
       subversion repository as per the instructions in
       Catalyst::Manual::Tutorial::01_Intro.

CREATE A CATALYST PROJECT
       Catalyst provides a number of helper scripts that can be used to
       quickly flesh out the basic structure of your application. All Catalyst
       projects begin with the "catalyst.pl" helper (see Catalyst::Helper for
       more information on helpers).  Also note that as of Catalyst 5.7000,
       you will not have the helper scripts unless you install both
       Catalyst::Runtime and Catalyst::Devel.

       In this first chapter of the tutorial, use the Catalyst "catalyst.pl"
       script to initialize the framework for an application called "Hello":

	   $ catalyst.pl Hello
	   created "Hello"
	   created "Hello/script"
	   created "Hello/lib"
	   created "Hello/root"
	   ...
	   created "Hello/script/hello_create.pl"
	   Change to application directory and Run "perl Makefile.PL" to make sure your install is complete
	   $ cd Hello

       Note: If you are using Strawberry Perl on Win32, drop the ".pl" from
       the end of the "catalyst.pl" command and simply use "catalyst Hello".

       The "catalyst.pl" helper script will display the names of the
       directories and files it creates:

	   Changes		 # Record of application changes
	   lib			 # Lib directory for your app's Perl modules
	       Hello		 # Application main code directory
		   Controller	 # Directory for Controller modules
		   Model	 # Directory for Models
		   View		 # Directory for Views
	       Hello.pm		 # Base application module
	   Makefile.PL		 # Makefile to build application
	   hello.conf		 # Application configuration file
	   README		 # README file
	   root			 # Equiv of htdocs, dir for templates, css, javascript
	       favicon.ico
	       static		 # Directory for static files
		   images	 # Directory for image files used in welcome screen
	   script		 # Directory for Perl scripts
	       hello_cgi.pl	 # To run your app as a cgi (not recommended)
	       hello_create.pl	 # To create models, views, controllers
	       hello_fastcgi.pl	 # To run app as a fastcgi program
	       hello_server.pl	 # The normal development server
	       hello_test.pl	 # Test your app from the command line
	   t			 # Directory for tests
	       01app.t		 # Test scaffold
	       02pod.t
	       03podcoverage.t

       Catalyst will "auto-discover" modules in the Controller, Model, and
       View directories. When you use the "hello_create.pl" script it will
       create Perl module scaffolds in those directories, plus test files in
       the "t" directory. The default location for templates is in the "root"
       directory. The scripts in the script directory will always start with
       the lowercased version of your application name. If your app is MaiTai,
       then the create script would be "maitai_create.pl".

       Though it's too early for any significant celebration, we already have
       a functioning application. We can use the Catalyst supplied script to
       start up a development server and view the default Catalyst page in
       your browser. All scripts in the script directory should be run from
       the base directory of your application, so change to the Hello
       directory.

       Run the following command to start up the built-in development web
       server (make sure you didn't forget the ""cd Hello"" from the previous
       step):

       Note: The "-r" argument enables reloading on code changes so you don't
       have to stop and start the server when you update code. See "perldoc
       script/hello_server.pl" or "script/hello_server.pl --help" for
       additional options you might find helpful. Most of the rest of the
       tutorial will assume that you are using "-r" when you start the
       development server, but feel free to manually start and stop it (use
       "Ctrl-C" to breakout of the dev server) if you prefer.

	   $ script/hello_server.pl -r
	   [debug] Debug messages enabled
	   [debug] Statistics enabled
	   [debug] Loaded plugins:
	   .----------------------------------------------------------------------------.
	   | Catalyst::Plugin::ConfigLoader  0.30					|
	   '----------------------------------------------------------------------------'

	   [debug] Loaded dispatcher "Catalyst::Dispatcher"
	   [debug] Loaded engine "Catalyst::Engine"
	   [debug] Found home "/home/catalyst/Hello"
	   [debug] Loaded Config "/home/catalyst/Hello/hello.conf"
	   [debug] Loaded components:
	   .-----------------------------------------------------------------+----------.
	   | Class							     | Type	|
	   +-----------------------------------------------------------------+----------+
	   | Hello::Controller::Root					     | instance |
	   '-----------------------------------------------------------------+----------'

	   [debug] Loaded Private actions:
	   .----------------------+--------------------------------------+--------------.
	   | Private		  | Class				 | Method	|
	   +----------------------+--------------------------------------+--------------+
	   | /default		  | Hello::Controller::Root		 | default	|
	   | /end		  | Hello::Controller::Root		 | end		|
	   | /index		  | Hello::Controller::Root		 | index	|
	   '----------------------+--------------------------------------+--------------'

	   [debug] Loaded Path actions:
	   .-------------------------------------+--------------------------------------.
	   | Path				 | Private				|
	   +-------------------------------------+--------------------------------------+
	   | /					 | /index				|
	   | /					 | /default				|
	   '-------------------------------------+--------------------------------------'

	   [info] Hello powered by Catalyst 5.90002
	   HTTP::Server::PSGI: Accepting connections at http://0:3000/

       Point your web browser to <http://localhost:3000> (substituting a
       different hostname or IP address as appropriate) and you should be
       greeted by the Catalyst welcome screen (if you get some other welcome
       screen or an "Index" screen, you probably forgot to specify port 3000
       in your URL).  Information similar to the following should be appended
       to the logging output of the development server:

	   [info] Hello powered by Catalyst 5.90002
	   HTTP::Server::PSGI: Accepting connections at http://0:3000/
	   [info] *** Request 1 (0.067/s) [19026] [Tue Aug 30 17:24:32 2011] ***
	   [debug] "GET" request for "/" from "192.168.245.2"
	   [debug] Path is "/"
	   [debug] Response Code: 200; Content-Type: text/html; charset=utf-8; Content-Length: 5613
	   [info] Request took 0.040895s (24.453/s)
	   .------------------------------------------------------------+-----------.
	   | Action							| Time	    |
	   +------------------------------------------------------------+-----------+
	   | /index							| 0.000916s |
	   | /end							| 0.000877s |
	   '------------------------------------------------------------+-----------'

       Note: Press "Ctrl-C" to break out of the development server if
       necessary.

HELLO WORLD
   The Simplest Way
       The Root.pm controller is a place to put global actions that usually
       execute on the root URL. Open the "lib/Hello/Controller/Root.pm" file
       in your editor. You will see the "index" subroutine, which is
       responsible for displaying the welcome screen that you just saw in your
       browser.

	   sub index :Path :Args(0) {
	       my ( $self, $c ) = @_;

	       # Hello World
	       $c->response->body( $c->welcome_message );
	   }

       Later on you'll want to change that to something more reasonable, such
       as a "404" message or a redirect, but for now just leave it alone.

       The "$c" here refers to the Catalyst context, which is used to access
       the Catalyst application. In addition to many other things, the
       Catalyst context provides access to "response" and "request" objects.
       (See Catalyst::Runtime, Catalyst::Response, and Catalyst::Request)

       "$c->response->body" sets the HTTP response (see Catalyst::Response),
       while "$c->welcome_message" is a special method that returns the
       welcome message that you saw in your browser.

       The ":Path :Args(0)" after the method name are attributes which
       determine which URLs will be dispatched to this method. (You might see
       ":Private" if you are using an older version of Catalyst, but using
       that with "default" or "index" is currently deprecated.	If so, you
       should also probably upgrade before continuing the tutorial.)

       Some MVC frameworks handle dispatching in a central place. Catalyst, by
       policy, prefers to handle URL dispatching with attributes on controller
       methods. There is a lot of flexibility in specifying which URLs to
       match.  This particular method will match all URLs, because it doesn't
       specify the path (nothing comes after "Path"), but will only accept a
       URL without any args because of the ":Args(0)".

       The default is to map URLs to controller names, and because of the way
       that Perl handles namespaces through package names, it is simple to
       create hierarchical structures in Catalyst. This means that you can
       create controllers with deeply nested actions in a clean and logical
       way. For example, the URL "http://hello.com/admin/articles/create" maps
       to the package "Hello::Controller::Admin::Articles", and the "create"
       method.

       While you leave the "script/hello_server.pl -r" command running the
       development server in one window (don't forget the "-r" on the end!),
       open another window and add the following subroutine to your
       "lib/Hello/Controller/Root.pm" file:

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

	       $c->response->body("Hello, World!");
	   }

       TIP: See Appendix 1 for tips on removing the leading spaces when
       cutting and pasting example code from POD-based documents.

       Notice in the window running the Development Server that you should get
       output similar to the following:

	   Saw changes to the following files:
	    - /home/catalyst/Hello/lib/Hello/Controller/Root.pm (modify)

	   Attempting to restart the server
	   ...
	   [debug] Loaded Private actions:
	   .----------------------+--------------------------------------+--------------.
	   | Private		  | Class				 | Method	|
	   +----------------------+--------------------------------------+--------------+
	   | /default		  | Hello::Controller::Root		 | default	|
	   | /end		  | Hello::Controller::Root		 | end		|
	   | /index		  | Hello::Controller::Root		 | index	|
	   | /hello		  | Hello::Controller::Root		 | hello	|
	   '----------------------+--------------------------------------+--------------'
	   ...

       The development server noticed the change in "Hello::Controller::Root"
       and automatically restarted itself.

       Go to <http://localhost:3000/hello> to see "Hello, World!".   Also
       notice that the newly defined 'hello' action is listed under "Loaded
       Private actions" in the development server debug output.

   Hello, World! Using a View and a Template
       In the Catalyst world a "View" itself is not a page of XHTML or a
       template designed to present a page to a browser. Rather, it is the
       module that determines the type of view -- HTML, pdf, XML, etc. For the
       thing that generates the content of that view (such as a Toolkit
       Template template file), the actual templates go under the "root"
       directory.

       To create a TT view, run:

	   $ script/hello_create.pl view HTML TT

       This creates the "lib/Hello/View/HTML.pm" module, which is a subclass
       of "Catalyst::View::TT".

       ·   The "view" keyword tells the create script that you are creating a
	   view.

       ·   The first argument "HTML" tells the script to name the View module
	   "HTML.pm", which is a commonly used name for TT views.  You can
	   name it anything you want, such as "MyView.pm". If you have more
	   than one view, be sure to set the default_view in Hello.pm (See
	   Catalyst::View::TT for more details on setting this).

       ·   The final "TT" tells Catalyst the type of the view, with "TT"
	   indicating that you want to a Template Toolkit view.

       If you look at "lib/Hello/View/HTML.pm" you will find that it only
       contains a config statement to set the TT extension to ".tt".

       Now that the HTML.pm "View" exists, Catalyst will autodiscover it and
       be able to use it to display the view templates using the "process"
       method that it inherits from the "Catalyst::View::TT" class.

       Template Toolkit is a very full featured template facility, with
       excellent documentation at http://template-toolkit.org/
       <http://template-toolkit.org/>, but since this is not a TT tutorial,
       we'll stick to only basic TT usage here (and explore some of the more
       common TT features in later chapters of the tutorial).

       Create a "root/hello.tt" template file (put it in the "root" under the
       "Hello" directory that is the base of your application). Here is a
       simple sample:

	   <p>
	       This is a TT view template, called '[% template.name %]'.
	   </p>

       [% and %] are markers for the TT parts of the template. Inside you can
       access Perl variables and classes, and use TT directives. In this case,
       we're using a special TT variable that defines the name of the template
       file ("hello.tt").  The rest of the template is normal HTML.

       Change the hello method in "lib/Hello/Controller/Root.pm" to the
       following:

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

	       $c->stash(template => 'hello.tt');
	   }

       This time, instead of doing "$c->response->body()", you are setting the
       value of the "template" hash key in the Catalyst "stash", an area for
       putting information to share with other parts of your application. The
       "template" key determines which template will be displayed at the end
       of the request cycle. Catalyst controllers have a default "end" action
       for all methods which causes the first (or default) view to be rendered
       (unless there's a "$c->response- >body()" statement). So your template
       will be magically displayed at the end of your method.

       After saving the file, the development server should automatically
       restart (again, the tutorial is written to assume that you are using
       the "-r" option -- manually restart it if you aren't), and look at
       <http://localhost:3000/hello> in your again. You should see the
       template that you just made.

       TIP: If you keep the server running with "-r" in a "background window,"
       don't let that window get totally hidden... if you have an syntax error
       in your code, the debug server output will contain the error
       information.

       Note: You will probably run into a variation of the "stash" statement
       above that looks like:

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

       Although this style is still relatively common, the approach we used
       previous is becoming more common because it allows you to set multiple
       stash variables in one line.  For example:

	   $c->stash(template => 'hello.tt', foo => 'bar',
		     another_thing => 1);

       You can also set multiple stash values with a hashref:

	   $c->stash({template => 'hello.tt', foo => 'bar',
		     another_thing => 1});

       Any of these formats work, but the "$c->stash(name => value);" style is
       growing in popularity -- you may wish to use it all the time (even when
       you are only setting a single value).

CREATE A SIMPLE CONTROLLER AND AN ACTION
       Create a controller named "Site" by executing the create script:

	   $ script/hello_create.pl controller Site

       This will create a "lib/Hello/Controller/Site.pm" file (and a test
       file). Bring Site.pm up in your editor, and you can see that there's
       not much there.

       In "lib/Hello/Controller/Site.pm", add the following method:

	   sub test :Local {
	       my ( $self, $c ) = @_;

	       $c->stash(username => 'John',
			 template => 'site/test.tt');
	   }

       Notice the "Local" attribute on the "test" method. This will cause the
       "test" action (now that we have assigned an "action type" to the method
       it appears as a "controller action" to Catalyst) to be executed on the
       "controller/method" URL, or, in this case, "site/test".	We will see
       additional information on controller actions throughout the rest of the
       tutorial, but if you are curious take a look at "Actions" in
       Catalyst::Manual::Intro.

       It's not actually necessary to set the template value as we do here.
       By default TT will attempt to render a template that follows the naming
       pattern "controller/method.tt", and we're following that pattern here.
       However, in other situations you will need to specify the template
       (such as if you've "forwarded" to the method, or if it doesn't follow
       the default naming convention).

       We've also put the variable "username" into the stash, for use in the
       template.

       Make a subdirectory "site" in the "root" directory.

	   $ mkdir root/site

       Create a new template file in that direction named "root/site/test.tt"
       and include a line like:

	   <p>Hello, [% username %]!</p>

       Once the server automatically restarts, notice in the server output
       that "/site/test" is listed in the Loaded Path actions.	Go to
       <http://localhost:3000/site/test> in your browser and you should see
       your test.tt file displayed, including the name "John" that you set in
       the controller.

       You can jump to the next chapter of the tutorial here: More Catalyst
       Basics

AUTHORS
       Gerda Shank, "gerda.shank@gmail.com" Kennedy Clark, "hkclark@gmail.com"

       Feel free to contact the author for any errors or suggestions, but the
       best way to report issues is via the CPAN RT Bug system at
       https://rt.cpan.org/Public/Dist/Display.html?Name=Catalyst-Manual
       <https://rt.cpan.org/Public/Dist/Display.html?Name=Catalyst-Manual>.

       Copyright 2006-2011, Kennedy Clark, under the Creative Commons
       Attribution Share-Alike License Version 3.0
       (http://creativecommons.org/licenses/by-sa/3.0/us/
       <http://creativecommons.org/licenses/by-sa/3.0/us/>).

perl v5.14.2		      Catalyst::Manual::Tutorial::02_CatalystBasics(3)
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