minor ambiguity report, thanks asarch

[catagits/Catalyst-Manual.git] / lib / Catalyst / Manual / Tutorial / 02_CatalystBasics.pod

=head1 NAME

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


=head1 OVERVIEW

This is B<Chapter 2 of 10> for the Catalyst tutorial.

L<Tutorial Overview|Catalyst::Manual::Tutorial>

=over 4

=item 1

L<Introduction|Catalyst::Manual::Tutorial::01_Intro>

=item 2

B<02_Catalyst Basics>

=item 3

L<More Catalyst Basics|Catalyst::Manual::Tutorial::03_MoreCatalystBasics>

=item 4

L<Basic CRUD|Catalyst::Manual::Tutorial::04_BasicCRUD>

=item 5

L<Authentication|Catalyst::Manual::Tutorial::05_Authentication>

=item 6

L<Authorization|Catalyst::Manual::Tutorial::06_Authorization>

=item 7

L<Debugging|Catalyst::Manual::Tutorial::07_Debugging>

=item 8

L<Testing|Catalyst::Manual::Tutorial::08_Testing>

=item 9

L<Advanced CRUD|Catalyst::Manual::Tutorial::09_AdvancedCRUD>

=item 10

L<Appendices|Catalyst::Manual::Tutorial::10_Appendices>

=back


=head1 DESCRIPTION

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

=over 4

=item * Helper Scripts

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

=item * 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
L<Catalyst::Manual::About|Catalyst::Manual::About>). In short:

=over 4

=item * 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.

=item * 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.

=item * Controller

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

=back

=item * 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.

=back

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


=head1 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 C<catalyst.pl> helper (see 
L<Catalyst::Helper|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 L<Catalyst::Runtime|Catalyst::Runtime> 
and L<Catalyst::Devel|Catalyst::Devel>.

In this first chapter of the tutorial, use the Catalyst C<catalyst.pl> 
script to initialize the framework for an application called C<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 C<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 "C<cd Hello>" from the 
previous step):

B<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 
C<perldoc script/hello_server.pl> or C<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 C<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  0.27                                       |
    '----------------------------------------------------------------------------'
    
    [debug] Loaded dispatcher "Catalyst::Dispatcher"
    [debug] Loaded engine "Catalyst::Engine::HTTP"
    [debug] Found home "/home/me/Hello"
    [debug] Loaded Config "/home/me/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 5.80020
    You can connect to your server at http://debian:3000

Point your web browser to L<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] *** Request 1 (0.001/s) [23194] [Sat Jan 16 11:09:18 2010] ***
    [debug] "GET" request for "/" from "127.0.0.1"
    [debug] Path is "/"
    [info] Request took 0.004851s (206.143/s)
    .------------------------------------------------------------+-----------.
    | Action                                                     | Time      |
    +------------------------------------------------------------+-----------+
    | /index                                                     | 0.000395s |
    | /end                                                       | 0.000425s |
    '------------------------------------------------------------+-----------'

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


=head1 HELLO WORLD

=head2 The Simplest Way

The Root.pm controller is a place to put global actions that usually 
execute on the root URL. Open the C<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<$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 L<Catalyst|Catalyst>, 
L<Catalyst::Response|Catalyst::Response>, and 
L<Catalyst::Request|Catalyst::Request>) 

C<$c-E<gt>response-E<gt>body> sets the HTTP response (see 
L<Catalyst::Response|Catalyst::Response>), while 
C<$c-E<gt>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 C<http://hello.com/admin/articles/create> 
maps to the package C<Hello::Controller::Admin::Articles>, and the 
C<create> method. 

Add the following subroutine to your C<lib/Hello/Controller/Root.pm> 
file:

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

Once you restart the server, you will need to use the new address
L<http://localhost:3000/hello> instead of L<http://localhost:3000/> to see the
changes.

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

Here you're sending your own string to the webpage.

Save the file, and you should notice the following in your server output:

    Saw changes to the following files:
     - /home/me/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        |
    '----------------------+--------------------------------------+--------------'
    
    [debug] Loaded Path actions:
    .-------------------------------------+--------------------------------------.
    | Path                                | Private                              |
    +-------------------------------------+--------------------------------------+
    | /                                   | /index                               |
    | /                                   | /default                             |
    | /hello                              | /hello                               |
    '-------------------------------------+--------------------------------------'
    ...

Go to L<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.


=head2 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 I<type> of view -- HTML, pdf, XML, etc. For 
the thing that generates the I<content> of that view (such as the 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 C<lib/Hello/View/HTML.pm> module, which is a subclass of 
C<Catalyst::View::TT>. 

=over 4

=item *

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

=item *

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 L<Catalyst::View::TT|Catalyst::View::TT> for more
details on setting this).

=item *

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

=back

If you look at C<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 C<Catalyst::View::TT> class.

Template Toolkit is a very full featured template facility, with 
excellent documentation at L<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 C<root/hello.tt> template file (put it in the C<root> under 
the C<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 (C<hello.tt>).  The rest of the template is normal HTML. 

Change the hello method in C<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<$c-E<gt>response-E<gt>body()>, you are 
setting the value of the "template" hash key in the Catalyst "stash", 
an area for putting information to share with other parts of your 
application. The "template" key determines which template will be 
displayed at the end of the request cycle. Catalyst controllers have a 
default "end" action for all methods which causes the first (or 
default) view to be rendered (unless there's a C<$c-E<gt>response-
E<gt>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 L<http://localhost:3000/hello> in your again. You 
should see the template that you just made.

B<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.

B<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<$c-E<gt>stash(name =E<gt> value);>
style is growing in popularity -- you may wish to use it all the 
time (even when you are only setting a single value).


=head1 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 C<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 C<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 C<test> method. This will cause 
the C<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 
L<Catalyst::Manual::Intro/Actions>.

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. Copy the hello.tt 
file into the directory as C<root/site/test.tt>, or create a new 
template file at that location. Include a line like: 

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

You should see your test.tt file displayed, including the name "John"
that you set in the controller.

Once the server automatically restarts, notice in the server 
output that C</site/test> is listed in the Loaded Path actions. 
Go to L<http://localhost:3000/site/test> in your browser.


=head1 AUTHORS

Gerda Shank, C<gerda.shank@gmail.com>
Kennedy Clark, C<hkclark@gmail.com>

Please report any errors, issues or suggestions to the author.  The
most recent version of the Catalyst Tutorial can be found at
L<http://dev.catalyst.perl.org/repos/Catalyst/Catalyst-Manual/5.80/trunk/lib/Catalyst/Manual/Tutorial/>.

Copyright 2006-2010, Kennedy Clark, under Creative Commons License
(L<http://creativecommons.org/licenses/by-sa/3.0/us/>).