3 Catalyst::Manual::Tutorial::CatalystBasics - Catalyst Tutorial - Part 2: Catalyst Application Development Basics
8 This is B<Part 2 of 10> for the Catalyst tutorial.
10 L<Tutorial Overview|Catalyst::Manual::Tutorial>
16 L<Introduction|Catalyst::Manual::Tutorial::Intro>
24 L<More Catalyst Basics|Catalyst::Manual::Tutorial::MoreCatalystBasics>
28 L<Basic CRUD|Catalyst::Manual::Tutorial::BasicCRUD>
32 L<Authentication|Catalyst::Manual::Tutorial::Authentication>
36 L<Authorization|Catalyst::Manual::Tutorial::Authorization>
40 L<Debugging|Catalyst::Manual::Tutorial::Debugging>
44 L<Testing|Catalyst::Manual::Tutorial::Testing>
48 L<Advanced CRUD|Catalyst::Manual::Tutorial::AdvancedCRUD>
52 L<Appendices|Catalyst::Manual::Tutorial::Appendices>
59 In this part of the tutorial, we will create a very basic Catalyst web
60 application, demonstrating a number of powerful capabilities, such as:
64 =item * Helper Scripts
66 Catalyst helper scripts that can be used to rapidly bootstrap the
67 skeletal structure of an application.
71 Model/View/Controller (MVC) provides an architecture that facilitates a
72 clean "separation of control" between the different portions of your
73 application. Given that many other documents cover this subject in
74 detail, MVC will not be discussed in depth here (for an excellent
75 introduction to MVC and general Catalyst concepts, please see
76 L<Catalyst::Manual::About|Catalyst::Manual::About>). In short:
82 The model usually represents a data store. In most applications, the
83 model equates to the objects that are created from and saved to your SQL
88 The view takes model objects and renders them into something for the end
89 user to look at. Normally this involves a template-generation tool that
90 creates HTML for the user's web browser, but it could easily be code
91 that generates other forms such as PDF documents, e-mails, spreadsheets,
92 or even "behind the scenes" formats such as XML and JSON.
96 As suggested by its name, the controller takes user requests and routes
97 them to the necessary model and view.
103 The use of Object-Relational Mapping (ORM) technology for database
104 access. Specifically, ORM provides an automated and standardized means
105 to persist and restore objects to/from a relational database.
109 You can checkout the source code for this example from the catalyst
110 subversion repository as per the instructions in
111 L<Catalyst::Manual::Tutorial::Intro|Catalyst::Manual::Tutorial::Intro>.
114 =head1 CREATE A CATALYST PROJECT
116 Catalyst provides a number of helper scripts that can be used to
117 quickly flesh out the basic structure of your application. All
118 Catalyst projects begin with the C<catalyst.pl> helper (see
119 L<Catalyst::Helper|Catalyst::Helper> for more information on helpers).
120 Also note that as of Catalyst 5.7000, you will not have the helper
121 scripts unless you install both L<Catalyst::Runtime|Catalyst::Runtime>
122 and L<Catalyst::Devel|Catalyst::Devel>.
124 In this first part of the tutorial, use the Catalyst
125 C<catalyst.pl> script to initialize the framework for an
126 application called C<Hello>:
130 created "Hello/script"
134 created "Hello/script/hello_create.pl"
137 The C<catalyst.pl> helper script will display the names of the
138 directories and files it creates:
140 Changes # Record of application changes
141 lib # Lib directory for your app's Perl modules
142 Hello # Application main code directory
143 Controller # Directory for Controller modules
144 Model # Directory for Models
145 View # Directory for Views
146 Hello.pm # Base application module
147 Makefile.PL # Makefile to build application
148 hello.conf # Application configuration file
150 root # Equiv of htdocs, dir for templates, css, javascript
152 static # Directory for static files
153 images # Directory for image files used in welcome screen
154 script # Directory for Perl scripts
155 hello_cgi.pl # To run your app as a cgi (not recommended)
156 hello_create.pl # To create models, views, controllers
157 hello_fastcgi.pl # To run app as a fastcgi program
158 hello_server.pl # The normal development server
159 hello_test.pl # Test your app from the command line
160 t # Directory for tests
161 01app.t # Test scaffold
166 Catalyst will "auto-discover" modules in the Controller, Model, and
167 View directories. When you use the hello_create.pl script it will
168 create Perl module scaffolds in those directories, plus test files in
169 the "t" directory. The default location for templates is in the "root"
170 directory. The scripts in the script directory will always start with
171 the lowercased version of your application name. If your app is
172 MaiTai, then the create script would be "maitai_create.pl".
174 Though it's too early for any significant celebration, we already have
175 a functioning application. We can use the Catalyst supplied script to
176 start up a development server and view the default Catalyst page in
177 your browser. All scripts in the script directory should be run from
178 the base directory of your application, so change to the Hello
181 Run the following command to start up the built-in development web
184 $ script/hello_server.pl
185 [debug] Debug messages enabled
186 [debug] Statistics enabled
187 [debug] Loaded plugins:
188 .----------------------------------------------------------------------------.
189 | Catalyst::Plugin::ConfigLoader 0.20 |
190 | Catalyst::Plugin::Static::Simple 0.20 |
191 '----------------------------------------------------------------------------'
193 [debug] Loaded dispatcher "Catalyst::Dispatcher"
194 [debug] Loaded engine "Catalyst::Engine::HTTP"
195 [debug] Found home "/home/me/Hello"
196 [debug] Loaded Config "/home/me/Hello/hello.conf"
197 [debug] Loaded components:
198 .-----------------------------------------------------------------+----------.
200 +-----------------------------------------------------------------+----------+
201 | Hello::Controller::Root | instance |
202 '-----------------------------------------------------------------+----------'
204 [debug] Loaded Private actions:
205 .----------------------+--------------------------------------+--------------.
206 | Private | Class | Method |
207 +----------------------+--------------------------------------+--------------+
208 | /default | Hello::Controller::Root | default |
209 | /end | Hello::Controller::Root | end |
210 '----------------------+--------------------------------------+--------------'
212 [debug] Loaded Path actions:
213 .-------------------------------------+--------------------------------------.
215 +-------------------------------------+--------------------------------------+
218 '-------------------------------------+--------------------------------------'
220 [info] Hello powered by Catalyst 5.7014
221 You can connect to your server at http://localhost:3000
223 Point your web browser to
224 L<http://localhost:3000|http://localhost:3000> (substituting a
225 different hostname or IP address as appropriate) and you should be
226 greeted by the Catalyst welcome screen. Information similar to the
227 following should be appended to the logging output of the development
230 [info] *** Request 1 (1.000/s) [10301] [Sun Nov 23 10:11:36 2008] ***
231 [debug] "GET" request for "/" from "127.0.0.1"
232 [info] Request took 0.017964s (55.667/s)
233 .----------------------------------------------------------------+-----------.
235 +----------------------------------------------------------------+-----------+
236 | /default | 0.000540s |
238 '----------------------------------------------------------------+-----------'
240 Press Ctrl-C to break out of the development server.
245 =head2 The Simplest Way
247 The Root.pm controller is a place to put global actions that usually
248 execute on the root URL. Open the C<lib/Hello/Controller/Root.pm> file in
249 your editor. You will see the "index" subroutine, which is
250 responsible for displaying the welcome screen that you just saw in
251 your browser. Later on you'll want to change that to something more
252 reasonable, such as a "404" message or a redirect, but for now just
255 sub index :Path :Args(0) {
256 my ( $self, $c ) = @_;
259 $c->response->body( $c->welcome_message );
262 The "C<$c>" here refers to the Catalyst context, which is used to
263 access the Catalyst application. In addition to many other things,
264 the Catalyst context provides access to "response" and "request"
265 objects. (See L<Catalyst|Catalyst>,
266 L<Catalyst::Response|Catalyst::Response>, and
267 L<Catalyst::Request|Catalyst::Request>)
269 C<$c-E<gt>response-E<gt>body> sets the HTTP response (see
270 L<Catalyst::Response|Catalyst::Response>), while C<$c-E<gt>welcome_message>
271 is a special method that returns the welcome message that you saw in
274 The ":Path :Args(0)" after the method name are attributes which determine
275 which URLs will be dispatched to this method. (Depending on your version of
276 Catalyst, it used to say "Private" but using that with 'default' or 'index'
277 is currently deprecated.)
279 Some MVC frameworks handle dispatching in a central place. Catalyst,
280 by policy, prefers to handle URL dispatching with attributes on
281 controller methods. There is a lot of flexibility in specifying which
282 URLs to match. This particular method will match all URLs, because it
283 doesn't specify the path (nothing comes after "Path"), but will only
284 accept a single args because of the ":Args(0)".
286 The default is to map URLs to controller names, and because of
287 the way that Perl handles namespaces through package names,
288 it is simple to create hierarchical structures in
289 Catalyst. This means that you can create controllers with deeply
290 nested actions in a clean and logical way.
292 For example, the URL C<http://hello.com/admin/articles/create> maps
293 to the package C<Hello::Controller::Admin::Articles>, and the C<create>
296 Add the following subroutine to your C<lib/Hello/Controller/Root.pm>
300 my ( $self, $c ) = @_;
302 $c->response->body("Hello, World!");
305 Here you're sending your own string to the webpage.
307 Save the file, start the server (stop and restart it if it's still
308 up), and go to L<http://localhost:3000/hello> to
312 =head2 Hello, World! Using a View and a Template
314 In the Catalyst world a "View" is not a page of XHTML or a template
315 designed to present a page to a browser. It is the module that
316 determines the I<type> of view -- HTML, pdf, XML, etc. For the
317 thing that generates the I<content> of that view, (such as the
318 default Toolkit Template) the actual templates go under the
321 To create a TT view, run:
323 $ script/hello_create.pl view TT TT
325 This creates the C<lib/Hello/View/TT.pm> module, which is a subclass of
326 C<Catalyst::View::TT>. The "view" keyword tells the create script that
327 you are creating a view, the second "TT" tells it that you are creating
328 a Template Toolkit view, and the first "TT" tells the script to name
329 the View module "TT.pm", which is a commonly used name for TT views.
330 (You can name it anything you want, such as "HTML.pm".) If you look at
331 TT.pm, you will find that it only contains a config statement to set
332 the TT extension to ".tt".
334 Now that the TT.pm "View" exists, Catalyst will autodiscover it and be
335 able to use it to display the view templates, using the "process"
336 method that it inherits from the C<Catalyst::View::TT class>.
338 Template Toolkit is a very full featured template facility, with
339 excellent documentation at L<http://template-toolkit.org/>,
340 but since this is not a TT tutorial, we'll stick to only basic TT
341 usage here (and explore some of the more common TT features in later
342 parts of the tutorial).
344 Create a C<root/hello.tt> template file (put it in the C<root> under
345 the C<Hello> directory that is the base of your application). Here is
348 [% META title = 'Hello, World!' %]
350 This is a TT view template, located in the 'root/' directory.
353 [% and %] are markers for the TT parts of the template. Inside you can
354 access Perl variables and classes, and use TT directives. The rest of
355 the template is normal HTML. Change the hello method in
356 C<lib/Hello/Controller/Root.pm> to the following:
359 my ( $self, $c ) = @_;
361 $c->stash->{template} = 'hello.tt';
364 This time, instead of doing C<$c-E<gt>response->body()>, you are setting
365 the value of the "template" hash key in the Catalyst "stash", an area
366 for putting information to share with other parts of your application.
367 The "template" key determines which template will be displayed at the
368 end of the method. Catalyst controllers have a default "end" action
369 for all methods which causes the first (or default) view to be
370 rendered (unless there's a C<$c-E<gt>response->body()> statement). So your
371 template will be magically displayed at the end of your method.
373 After saving the file, restart the development server, and look at
374 L<http://localhost:3000/hello> again. You should
375 see the template that you just made.
378 =head1 CREATE A SIMPLE CONTROLLER AND AN ACTION
380 Create a controller named "Site" by executing the create script:
382 $ script/hello_create.pl controller Site
384 This will create a C<lib/Hello/Controller/Site.pm> file (and a test
385 file). Bring Site.pm up in your editor, and you can see that there's
386 not much there. Most people probably don't bother to use the create
387 script to make controllers after they're used to using Catalyst.
389 In C<lib/Hello/Controller/Site.pm>, add the following method:
392 my ( $self, $c ) = @_;
394 $c->stash->{username} = "John";
395 $c->stash->{template} = 'site/test.tt';
398 Notice the "Local" attribute on the method. This will allow the action
399 to be executed on the "controller/method" URL, or, in this case,
400 "site/test", instead of at the root site URL, like "Global". It's not
401 actually necessary to set the template value, since by default TT will
402 attempt to render a template that follows the naming pattern
403 "controller/method.tt", and we're following that pattern here, but in
404 other situations you will need to specify the template (such as if
405 you've "forwarded" to the method, or if it doesn't follow the default
406 naming convention). We've also put the variable "name" into the stash,
407 for use in the template.
409 Make a subdirectory "site" in the "root" directory. Copy the hello.tt
410 file into the directory as C<root/site/test.tt>, or create a new
411 template file at that location. Include a line like:
413 <p>Hello, [% username %]!</p>
415 Bring up or restart the server. Notice in the server output that
416 C</site/test> is listed in the Loaded Path actions. Go to
417 L<http://localhost:3000/site/test> in your browser.
419 You should see your test.tt file displayed, including the name "John"
420 that you set in the controller.
425 Gerda Shank, C<gerda.shank@gmail.com>
426 Kennedy Clark, C<hkclark@gmail.com>
428 Please report any errors, issues or suggestions to the author. The
429 most recent version of the Catalyst Tutorial can be found at
430 L<http://dev.catalyst.perl.org/repos/Catalyst/trunk/Catalyst-Manual/lib/Catalyst/Manual/Tutorial/>.
432 Copyright 2006-2008, Kennedy Clark & Gerda Shank, under Creative Commons License
433 (L<http://creativecommons.org/licenses/by-sa/3.0/us/>).