3 Catalyst::Manual::Tutorial::02_CatalystBasics - Catalyst Tutorial - Chapter 2: Catalyst Application Development Basics
8 This is B<Chapter 2 of 10> for the Catalyst tutorial.
10 L<Tutorial Overview|Catalyst::Manual::Tutorial>
16 L<Introduction|Catalyst::Manual::Tutorial::01_Intro>
24 L<More Catalyst Basics|Catalyst::Manual::Tutorial::03_MoreCatalystBasics>
28 L<Basic CRUD|Catalyst::Manual::Tutorial::04_BasicCRUD>
32 L<Authentication|Catalyst::Manual::Tutorial::05_Authentication>
36 L<Authorization|Catalyst::Manual::Tutorial::06_Authorization>
40 L<Debugging|Catalyst::Manual::Tutorial::07_Debugging>
44 L<Testing|Catalyst::Manual::Tutorial::08_Testing>
48 L<Advanced CRUD|Catalyst::Manual::Tutorial::09_AdvancedCRUD>
52 L<Appendices|Catalyst::Manual::Tutorial::10_Appendices>
59 In this chapter of the tutorial, we will create a very basic Catalyst
60 web application, demonstrating a number of powerful capabilities, such
65 =item * Helper Scripts
67 Catalyst helper scripts that can be used to rapidly bootstrap the
68 skeletal structure of an application.
72 Model/View/Controller (MVC) provides an architecture that facilitates a
73 clean "separation of control" between the different portions of your
74 application. Given that many other documents cover this subject in
75 detail, MVC will not be discussed in depth here (for an excellent
76 introduction to MVC and general Catalyst concepts, please see
77 L<Catalyst::Manual::About|Catalyst::Manual::About>). In short:
83 The model usually represents a data store. In most applications, the
84 model equates to the objects that are created from and saved to your SQL
89 The view takes model objects and renders them into something for the end
90 user to look at. Normally this involves a template-generation tool that
91 creates HTML for the user's web browser, but it could easily be code
92 that generates other forms such as PDF documents, e-mails, spreadsheets,
93 or even "behind the scenes" formats such as XML and JSON.
97 As suggested by its name, the controller takes user requests and routes
98 them to the necessary model and view.
104 The use of Object-Relational Mapping (ORM) technology for database
105 access. Specifically, ORM provides an automated and standardized means
106 to persist and restore objects to/from a relational database and will
107 automatically create our Catalyst model for use with a database.
111 You can checkout the source code for this example from the catalyst
112 subversion repository as per the instructions in
113 L<Catalyst::Manual::Tutorial::01_Intro|Catalyst::Manual::Tutorial::01_Intro>.
116 =head1 CREATE A CATALYST PROJECT
118 Catalyst provides a number of helper scripts that can be used to
119 quickly flesh out the basic structure of your application. All
120 Catalyst projects begin with the C<catalyst.pl> helper (see
121 L<Catalyst::Helper|Catalyst::Helper> for more information on helpers).
122 Also note that as of Catalyst 5.7000, you will not have the helper
123 scripts unless you install both L<Catalyst::Runtime|Catalyst::Runtime>
124 and L<Catalyst::Devel|Catalyst::Devel>.
126 In this first chapter of the tutorial, use the Catalyst C<catalyst.pl>
127 script to initialize the framework for an application called C<Hello>:
131 created "Hello/script"
135 created "Hello/script/hello_create.pl"
136 Change to application directory and Run "perl Makefile.PL" to make sure your install is complete
139 Note: If you are using Strawberry Perl on Win32, drop the ".pl"
140 from the end of the "catalyst.pl" command and simply use
143 The C<catalyst.pl> helper script will display the names of the
144 directories and files it creates:
146 Changes # Record of application changes
147 lib # Lib directory for your app's Perl modules
148 Hello # Application main code directory
149 Controller # Directory for Controller modules
150 Model # Directory for Models
151 View # Directory for Views
152 Hello.pm # Base application module
153 Makefile.PL # Makefile to build application
154 hello.conf # Application configuration file
156 root # Equiv of htdocs, dir for templates, css, javascript
158 static # Directory for static files
159 images # Directory for image files used in welcome screen
160 script # Directory for Perl scripts
161 hello_cgi.pl # To run your app as a cgi (not recommended)
162 hello_create.pl # To create models, views, controllers
163 hello_fastcgi.pl # To run app as a fastcgi program
164 hello_server.pl # The normal development server
165 hello_test.pl # Test your app from the command line
166 t # Directory for tests
167 01app.t # Test scaffold
172 Catalyst will "auto-discover" modules in the Controller, Model, and
173 View directories. When you use the hello_create.pl script it will
174 create Perl module scaffolds in those directories, plus test files in
175 the "t" directory. The default location for templates is in the "root"
176 directory. The scripts in the script directory will always start with
177 the lowercased version of your application name. If your app is
178 MaiTai, then the create script would be "maitai_create.pl".
180 Though it's too early for any significant celebration, we already have
181 a functioning application. We can use the Catalyst supplied script to
182 start up a development server and view the default Catalyst page in
183 your browser. All scripts in the script directory should be run from
184 the base directory of your application, so change to the Hello
187 Run the following command to start up the built-in development web
188 server (make sure you didn't forget the "C<cd Hello>" from the
191 B<Note>: The "-r" argument enables reloading on code changes so you
192 don't have to stop and start the server when you update code. See
193 C<perldoc script/hello_server.pl> or C<script/hello_server.pl --help>
194 for additional options you might find helpful. Most of the rest of the
195 tutorial will assume that you are using "-r" when you start the development
196 server, but feel free to manually start and stop it (use C<Ctrl-C> to
197 breakout of the dev server) if you prefer.
199 $ script/hello_server.pl -r
200 [debug] Debug messages enabled
201 [debug] Statistics enabled
202 [debug] Loaded plugins:
203 .----------------------------------------------------------------------------.
204 | Catalyst::Plugin::ConfigLoader 0.27 |
205 '----------------------------------------------------------------------------'
207 [debug] Loaded dispatcher "Catalyst::Dispatcher"
208 [debug] Loaded engine "Catalyst::Engine::HTTP"
209 [debug] Found home "/home/me/Hello"
210 [debug] Loaded Config "/home/me/Hello/hello.conf"
211 [debug] Loaded components:
212 .-----------------------------------------------------------------+----------.
214 +-----------------------------------------------------------------+----------+
215 | Hello::Controller::Root | instance |
216 '-----------------------------------------------------------------+----------'
218 [debug] Loaded Private actions:
219 .----------------------+--------------------------------------+--------------.
220 | Private | Class | Method |
221 +----------------------+--------------------------------------+--------------+
222 | /default | Hello::Controller::Root | default |
223 | /end | Hello::Controller::Root | end |
224 | /index | Hello::Controller::Root | index |
225 '----------------------+--------------------------------------+--------------'
227 [debug] Loaded Path actions:
228 .-------------------------------------+--------------------------------------.
230 +-------------------------------------+--------------------------------------+
233 '-------------------------------------+--------------------------------------'
235 [info] Hello powered by Catalyst 5.80020
236 You can connect to your server at http://debian:3000
238 Point your web browser to L<http://localhost:3000> (substituting a
239 different hostname or IP address as appropriate) and you should be
240 greeted by the Catalyst welcome screen (if you get some other welcome
241 screen or an "Index" screen, you probably forgot to specify port 3000
242 in your URL). Information similar to the following should be appended
243 to the logging output of the development server:
245 [info] *** Request 1 (0.001/s) [23194] [Sat Jan 16 11:09:18 2010] ***
246 [debug] "GET" request for "/" from "127.0.0.1"
248 [info] Request took 0.004851s (206.143/s)
249 .------------------------------------------------------------+-----------.
251 +------------------------------------------------------------+-----------+
252 | /index | 0.000395s |
254 '------------------------------------------------------------+-----------'
256 B<Note>: Press C<Ctrl-C> to break out of the development server if
262 =head2 The Simplest Way
264 The Root.pm controller is a place to put global actions that usually
265 execute on the root URL. Open the C<lib/Hello/Controller/Root.pm> file in
266 your editor. You will see the "index" subroutine, which is
267 responsible for displaying the welcome screen that you just saw in
270 sub index :Path :Args(0) {
271 my ( $self, $c ) = @_;
274 $c->response->body( $c->welcome_message );
277 Later on you'll want to change that to something more reasonable, such
278 as a "404" message or a redirect, but for now just leave it alone.
280 The "C<$c>" here refers to the Catalyst context, which is used to
281 access the Catalyst application. In addition to many other things,
282 the Catalyst context provides access to "response" and "request"
283 objects. (See L<Catalyst|Catalyst>,
284 L<Catalyst::Response|Catalyst::Response>, and
285 L<Catalyst::Request|Catalyst::Request>)
287 C<$c-E<gt>response-E<gt>body> sets the HTTP response (see
288 L<Catalyst::Response|Catalyst::Response>), while
289 C<$c-E<gt>welcome_message> is a special method that returns the
290 welcome message that you saw in your browser.
292 The ":Path :Args(0)" after the method name are attributes which
293 determine which URLs will be dispatched to this method. (You might see
294 ":Private" if you are using an older version of Catalyst, but using
295 that with "default" or "index" is currently deprecated. If so, you
296 should also probably upgrade before continuing the tutorial.)
298 Some MVC frameworks handle dispatching in a central place. Catalyst,
299 by policy, prefers to handle URL dispatching with attributes on
300 controller methods. There is a lot of flexibility in specifying which
301 URLs to match. This particular method will match all URLs, because it
302 doesn't specify the path (nothing comes after "Path"), but will only
303 accept a URL without any args because of the ":Args(0)".
305 The default is to map URLs to controller names, and because of the way
306 that Perl handles namespaces through package names, it is simple to
307 create hierarchical structures in Catalyst. This means that you can
308 create controllers with deeply nested actions in a clean and logical
309 way. For example, the URL C<http://hello.com/admin/articles/create>
310 maps to the package C<Hello::Controller::Admin::Articles>, and the
313 Add the following subroutine to your C<lib/Hello/Controller/Root.pm>
317 my ( $self, $c ) = @_;
319 $c->response->body("Hello, World!");
322 B<TIP>: See Appendix 1 for tips on removing the leading spaces when
323 cutting and pasting example code from POD-based documents.
325 Here you're sending your own string to the webpage.
327 Save the file, and you should notice the following in your server output:
329 Saw changes to the following files:
330 - /home/me/Hello/lib/Hello/Controller/Root.pm (modify)
332 Attempting to restart the server
334 [debug] Loaded Private actions:
335 .----------------------+--------------------------------------+--------------.
336 | Private | Class | Method |
337 +----------------------+--------------------------------------+--------------+
338 | /default | Hello::Controller::Root | default |
339 | /end | Hello::Controller::Root | end |
340 | /index | Hello::Controller::Root | index |
341 | /hello | Hello::Controller::Root | hello |
342 '----------------------+--------------------------------------+--------------'
344 [debug] Loaded Path actions:
345 .-------------------------------------+--------------------------------------.
347 +-------------------------------------+--------------------------------------+
351 '-------------------------------------+--------------------------------------'
354 Go to L<http://localhost:3000/hello> to see "Hello, World!". Also
355 notice that the newly defined 'hello' action is listed under "Loaded
356 Private actions" in the development server debug output.
359 =head2 Hello, World! Using a View and a Template
361 In the Catalyst world a "View" itself is not a page of XHTML or a
362 template designed to present a page to a browser. Rather, it is the
363 module that determines the I<type> of view -- HTML, pdf, XML, etc. For
364 the thing that generates the I<content> of that view (such as the a
365 Toolkit Template template file), the actual templates go under the
368 To create a TT view, run:
370 $ script/hello_create.pl view HTML TT
372 This creates the C<lib/Hello/View/HTML.pm> module, which is a subclass of
373 C<Catalyst::View::TT>.
379 The "view" keyword tells the create script that you are creating a view.
383 The first argument "HTML" tells the script to name the View module "HTML.pm",
384 which is a commonly used name for TT views. You can name it anything you want,
385 such as "MyView.pm". If you have more than one view, be sure to set the
386 default_view in Hello.pm (See L<Catalyst::View::TT|Catalyst::View::TT> for more
387 details on setting this).
391 The final "TT" tells Catalyst the I<type> of the view, with "TT"
392 indicating that you want to a Template Toolkit view.
396 If you look at C<lib/Hello/View/HTML.pm> you will find that it only
397 contains a config statement to set the TT extension to ".tt".
399 Now that the HTML.pm "View" exists, Catalyst will autodiscover it and be
400 able to use it to display the view templates using the "process"
401 method that it inherits from the C<Catalyst::View::TT> class.
403 Template Toolkit is a very full featured template facility, with
404 excellent documentation at L<http://template-toolkit.org/>,
405 but since this is not a TT tutorial, we'll stick to only basic TT
406 usage here (and explore some of the more common TT features in later
407 chapters of the tutorial).
409 Create a C<root/hello.tt> template file (put it in the C<root> under
410 the C<Hello> directory that is the base of your application). Here is
414 This is a TT view template, called '[% template.name %]'.
417 [% and %] are markers for the TT parts of the template. Inside you can
418 access Perl variables and classes, and use TT directives. In this
419 case, we're using a special TT variable that defines the name of the
420 template file (C<hello.tt>). The rest of the template is normal HTML.
422 Change the hello method in C<lib/Hello/Controller/Root.pm> to the
426 my ( $self, $c ) = @_;
428 $c->stash(template => 'hello.tt');
431 This time, instead of doing C<$c-E<gt>response-E<gt>body()>, you are
432 setting the value of the "template" hash key in the Catalyst "stash",
433 an area for putting information to share with other parts of your
434 application. The "template" key determines which template will be
435 displayed at the end of the request cycle. Catalyst controllers have a
436 default "end" action for all methods which causes the first (or
437 default) view to be rendered (unless there's a C<$c-E<gt>response-
438 E<gt>body()> statement). So your template will be magically displayed
439 at the end of your method.
441 After saving the file, the development server should automatically
442 restart (again, the tutorial is written to assume that you are
443 using the "-r" option -- manually restart it if you aren't),
444 and look at L<http://localhost:3000/hello> in your again. You
445 should see the template that you just made.
447 B<TIP:> If you keep the server running with "-r" in a "background
448 window," don't let that window get totally hidden... if you have an
449 syntax error in your code, the debug server output will contain the
452 B<Note:> You will probably run into a variation of the "stash"
453 statement above that looks like:
455 $c->stash->{template} = 'hello.tt';
457 Although this style is still relatively common, the approach we
458 used previous is becoming more common because it allows you to
459 set multiple stash variables in one line. For example:
461 $c->stash(template => 'hello.tt', foo => 'bar',
464 You can also set multiple stash values with a hashref:
466 $c->stash({template => 'hello.tt', foo => 'bar',
467 another_thing => 1});
469 Any of these formats work, but the C<$c-E<gt>stash(name =E<gt> value);>
470 style is growing in popularity -- you may wish to use it all the
471 time (even when you are only setting a single value).
474 =head1 CREATE A SIMPLE CONTROLLER AND AN ACTION
476 Create a controller named "Site" by executing the create script:
478 $ script/hello_create.pl controller Site
480 This will create a C<lib/Hello/Controller/Site.pm> file (and a test
481 file). Bring Site.pm up in your editor, and you can see that there's
484 In C<lib/Hello/Controller/Site.pm>, add the following method:
487 my ( $self, $c ) = @_;
489 $c->stash(username => 'John',
490 template => 'site/test.tt');
493 Notice the "Local" attribute on the C<test> method. This will cause
494 the C<test> action (now that we have assigned an "action type" to the
495 method it appears as a "controller action" to Catalyst) to be executed
496 on the "controller/method" URL, or, in this case, "site/test". We
497 will see additional information on controller actions throughout the
498 rest of the tutorial, but if you are curious take a look at
499 L<Catalyst::Manual::Intro/Actions>.
501 It's not actually necessary to set the template value as we do here.
502 By default TT will attempt to render a template that follows the
503 naming pattern "controller/method.tt", and we're following that
504 pattern here. However, in other situations you will need to specify
505 the template (such as if you've "forwarded" to the method, or if it
506 doesn't follow the default naming convention).
508 We've also put the variable "username" into the stash, for use in the
511 Make a subdirectory "site" in the "root" directory. Copy the hello.tt
512 file into the directory as C<root/site/test.tt>, or create a new
513 template file at that location. Include a line like:
515 <p>Hello, [% username %]!</p>
517 You should see your test.tt file displayed, including the name "John"
518 that you set in the controller.
520 Once the server automatically restarts, notice in the server
521 output that C</site/test> is listed in the Loaded Path actions.
522 Go to L<http://localhost:3000/site/test> in your browser.
527 Gerda Shank, C<gerda.shank@gmail.com>
528 Kennedy Clark, C<hkclark@gmail.com>
530 Please report any errors, issues or suggestions to the author. The
531 most recent version of the Catalyst Tutorial can be found at
532 L<http://dev.catalyst.perl.org/repos/Catalyst/Catalyst-Manual/5.80/trunk/lib/Catalyst/Manual/Tutorial/>.
534 Copyright 2006-2008, Kennedy Clark & Gerda Shank, under Creative Commons License
535 (L<http://creativecommons.org/licenses/by-sa/3.0/us/>).