1Catalyst::Manual::TutorUisaelr::C0o2n_tCCraaittbaaulltyyessdtt:BP:aeMsrailncusDa(ol3c:)u:mTeunttoartiiaoln::02_CatalystBasics(3)
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NAME

6       Catalyst::Manual::Tutorial::02_CatalystBasics - Catalyst Tutorial -
7       Chapter 2: Catalyst Application Development Basics
8

OVERVIEW

10       This is Chapter 2 of 10 for the Catalyst tutorial.
11
12       Tutorial Overview
13
14       1.  Introduction
15
16       2.  02_Catalyst Basics
17
18       3.  More Catalyst Basics
19
20       4.  Basic CRUD
21
22       5.  Authentication
23
24       6.  Authorization
25
26       7.  Debugging
27
28       8.  Testing
29
30       9.  Advanced CRUD
31
32       10. Appendices
33

DESCRIPTION

35       In this chapter of the tutorial, we will create a very basic Catalyst
36       web application, demonstrating a number of powerful capabilities, such
37       as:
38
39       •   Helper Scripts
40
41           Catalyst helper scripts that can be used to rapidly bootstrap the
42           skeletal structure of an application.
43
44       •   MVC
45
46           Model/View/Controller (MVC) provides an architecture that
47           facilitates a clean "separation of control" between the different
48           portions of your application. Given that many other documents cover
49           this subject in detail, MVC will not be discussed in depth here
50           (for an excellent introduction to MVC and general Catalyst
51           concepts, please see Catalyst::Manual::About). In short:
52
53           •   Model
54
55               The model usually represents a data store. In most
56               applications, the model equates to the objects that are created
57               from and saved to your SQL database.
58
59           •   View
60
61               The view takes model objects and renders them into something
62               for the end user to look at. Normally this involves a template-
63               generation tool that creates HTML for the user's web browser,
64               but it could easily be code that generates other forms such as
65               PDF documents, e-mails, spreadsheets, or even "behind the
66               scenes" formats such as XML and JSON.
67
68           •   Controller
69
70               As suggested by its name, the controller takes user requests
71               and routes them to the necessary model and view.
72
73       •   ORM
74
75           The use of Object-Relational Mapping (ORM) technology for database
76           access. Specifically, ORM provides an automated and standardized
77           means to persist and restore objects to/from a relational database
78           and will automatically create our Catalyst model for use with a
79           database.
80
81       You can checkout the source code for this example from the catalyst
82       subversion repository as per the instructions in
83       Catalyst::Manual::Tutorial::01_Intro.
84

CREATE A CATALYST PROJECT

86       Catalyst provides a number of helper scripts that can be used to
87       quickly flesh out the basic structure of your application. All Catalyst
88       projects begin with the catalyst.pl helper (see Catalyst::Helper for
89       more information on helpers).  Also note that as of Catalyst 5.7000,
90       you will not have the helper scripts unless you install both
91       Catalyst::Runtime and Catalyst::Devel.
92
93       In this first chapter of the tutorial, use the Catalyst catalyst.pl
94       script to initialize the framework for an application called "Hello":
95
96           $ catalyst.pl Hello
97           created "Hello"
98           created "Hello/script"
99           created "Hello/lib"
100           created "Hello/root"
101           ...
102           created "Hello/script/hello_create.pl"
103           Change to application directory and Run "perl Makefile.PL" to make sure your install is complete
104           $ cd Hello
105
106       Note: If you are using Strawberry Perl on Win32, drop the ".pl" from
107       the end of the "catalyst.pl" command and simply use "catalyst Hello".
108
109       The catalyst.pl helper script will display the names of the directories
110       and files it creates:
111
112           Changes               # Record of application changes
113           lib                   # Lib directory for your app's Perl modules
114               Hello             # Application main code directory
115                   Controller    # Directory for Controller modules
116                   Model         # Directory for Models
117                   View          # Directory for Views
118               Hello.pm          # Base application module
119           Makefile.PL           # Makefile to build application
120           hello.conf            # Application configuration file
121           README                # README file
122           root                  # Equiv of htdocs, dir for templates, css, javascript
123               favicon.ico
124               static            # Directory for static files
125                   images        # Directory for image files used in welcome screen
126           script                # Directory for Perl scripts
127               hello_cgi.pl      # To run your app as a cgi (not recommended)
128               hello_create.pl   # To create models, views, controllers
129               hello_fastcgi.pl  # To run app as a fastcgi program
130               hello_server.pl   # The normal development server
131               hello_test.pl     # Test your app from the command line
132           t                     # Directory for tests
133               01app.t           # Test scaffold
134               02pod.t
135               03podcoverage.t
136
137       Catalyst will "auto-discover" modules in the Controller, Model, and
138       View directories. When you use the hello_create.pl script it will
139       create Perl module scaffolds in those directories, plus test files in
140       the "t" directory. The default location for templates is in the "root"
141       directory. The scripts in the script directory will always start with
142       the lowercased version of your application name. If your app is MaiTai,
143       then the create script would be "maitai_create.pl".
144
145       Though it's too early for any significant celebration, we already have
146       a functioning application. We can use the Catalyst supplied script to
147       start up a development server and view the default Catalyst page in
148       your browser. All scripts in the script directory should be run from
149       the base directory of your application, so change to the Hello
150       directory.
151
152       Run the following command to start up the built-in development web
153       server (make sure you didn't forget the ""cd Hello"" from the previous
154       step):
155
156       Note: The "-r" argument enables reloading on code changes so you don't
157       have to stop and start the server when you update code. See "perldoc
158       script/hello_server.pl" or "script/hello_server.pl --help" for
159       additional options you might find helpful. Most of the rest of the
160       tutorial will assume that you are using "-r" when you start the
161       development server, but feel free to manually start and stop it (use
162       "Ctrl-C" to breakout of the dev server) if you prefer.
163
164           $ script/hello_server.pl -r
165           [debug] Debug messages enabled
166           [debug] Statistics enabled
167           [debug] Loaded plugins:
168           .----------------------------------------------------------------------------.
169           | Catalyst::Plugin::ConfigLoader  0.30                                       |
170           '----------------------------------------------------------------------------'
171
172           [debug] Loaded dispatcher "Catalyst::Dispatcher"
173           [debug] Loaded engine "Catalyst::Engine"
174           [debug] Found home "/home/catalyst/Hello"
175           [debug] Loaded Config "/home/catalyst/Hello/hello.conf"
176           [debug] Loaded components:
177           .-----------------------------------------------------------------+----------.
178           | Class                                                           | Type     |
179           +-----------------------------------------------------------------+----------+
180           | Hello::Controller::Root                                         | instance |
181           '-----------------------------------------------------------------+----------'
182
183           [debug] Loaded Private actions:
184           .----------------------+--------------------------------------+--------------.
185           | Private              | Class                                | Method       |
186           +----------------------+--------------------------------------+--------------+
187           | /default             | Hello::Controller::Root              | default      |
188           | /end                 | Hello::Controller::Root              | end          |
189           | /index               | Hello::Controller::Root              | index        |
190           '----------------------+--------------------------------------+--------------'
191
192           [debug] Loaded Path actions:
193           .-------------------------------------+--------------------------------------.
194           | Path                                | Private                              |
195           +-------------------------------------+--------------------------------------+
196           | /                                   | /index                               |
197           | /                                   | /default                             |
198           '-------------------------------------+--------------------------------------'
199
200           [info] Hello powered by Catalyst 5.90002
201           HTTP::Server::PSGI: Accepting connections at http://0:3000/
202
203       Point your web browser to <http://localhost:3000> (substituting a
204       different hostname or IP address as appropriate) and you should be
205       greeted by the Catalyst welcome screen (if you get some other welcome
206       screen or an "Index" screen, you probably forgot to specify port 3000
207       in your URL).  Information similar to the following should be appended
208       to the logging output of the development server:
209
210           [info] Hello powered by Catalyst 5.90002
211           HTTP::Server::PSGI: Accepting connections at http://0:3000/
212           [info] *** Request 1 (0.067/s) [19026] [Tue Aug 30 17:24:32 2011] ***
213           [debug] "GET" request for "/" from "192.168.245.2"
214           [debug] Path is "/"
215           [debug] Response Code: 200; Content-Type: text/html; charset=utf-8; Content-Length: 5613
216           [info] Request took 0.040895s (24.453/s)
217           .------------------------------------------------------------+-----------.
218           | Action                                                     | Time      |
219           +------------------------------------------------------------+-----------+
220           | /index                                                     | 0.000916s |
221           | /end                                                       | 0.000877s |
222           '------------------------------------------------------------+-----------'
223
224       Note: Press "Ctrl-C" to break out of the development server if
225       necessary.
226

HELLO WORLD

228   The Simplest Way
229       The Root.pm controller is a place to put global actions that usually
230       execute on the root URL. Open the lib/Hello/Controller/Root.pm file in
231       your editor. You will see the "index" subroutine, which is responsible
232       for displaying the welcome screen that you just saw in your browser.
233
234           sub index :Path :Args(0) {
235               my ( $self, $c ) = @_;
236
237               # Hello World
238               $c->response->body( $c->welcome_message );
239           }
240
241       Later on you'll want to change that to something more reasonable, such
242       as a "404" message or a redirect, but for now just leave it alone.
243
244       The "$c" here refers to the Catalyst context, which is used to access
245       the Catalyst application. In addition to many other things, the
246       Catalyst context provides access to "response" and "request" objects.
247       (See Catalyst::Runtime, Catalyst::Response, and Catalyst::Request)
248
249       "$c->response->body" sets the HTTP response (see Catalyst::Response),
250       while "$c->welcome_message" is a special method that returns the
251       welcome message that you saw in your browser.
252
253       The "":Path :Args(0)"" after the method name are attributes which
254       determine which URLs will be dispatched to this method. (You might see
255       ":Private" if you are using an older version of Catalyst, but using
256       that with "default" or "index" is currently deprecated.  If so, you
257       should also probably upgrade before continuing the tutorial.)
258
259       Some MVC frameworks handle dispatching in a central place. Catalyst, by
260       policy, prefers to handle URL dispatching with attributes on controller
261       methods. There is a lot of flexibility in specifying which URLs to
262       match.  This particular method will match all URLs, because it doesn't
263       specify the path (nothing comes after "Path"), but will only accept a
264       URL without any args because of the ":Args(0)".
265
266       The default is to map URLs to controller names, and because of the way
267       that Perl handles namespaces through package names, it is simple to
268       create hierarchical structures in Catalyst. This means that you can
269       create controllers with deeply nested actions in a clean and logical
270       way. For example, the URL "http://hello.com/admin/articles/create" maps
271       to the package "Hello::Controller::Admin::Articles", and the "create"
272       method.
273
274       While you leave the "script/hello_server.pl -r" command running the
275       development server in one window (don't forget the "-r" at the end!),
276       open another window and add the following subroutine to your
277       lib/Hello/Controller/Root.pm file:
278
279           sub hello :Global {
280               my ( $self, $c ) = @_;
281
282               $c->response->body("Hello, World!");
283           }
284
285       TIP: See Appendix 1 for tips on removing the leading spaces when
286       cutting and pasting example code from POD-based documents.
287
288       Notice in the window running the Development Server that you should get
289       output similar to the following:
290
291           Saw changes to the following files:
292            - /home/catalyst/Hello/lib/Hello/Controller/Root.pm (modify)
293
294           Attempting to restart the server
295           ...
296           [debug] Loaded Private actions:
297           .----------------------+--------------------------------------+--------------.
298           | Private              | Class                                | Method       |
299           +----------------------+--------------------------------------+--------------+
300           | /default             | Hello::Controller::Root              | default      |
301           | /end                 | Hello::Controller::Root              | end          |
302           | /index               | Hello::Controller::Root              | index        |
303           | /hello               | Hello::Controller::Root              | hello        |
304           '----------------------+--------------------------------------+--------------'
305           ...
306
307       The development server noticed the change in "Hello::Controller::Root"
308       and automatically restarted itself.
309
310       Go to <http://localhost:3000/hello> to see "Hello, World!".   Also
311       notice that the newly defined 'hello' action is listed under "Loaded
312       Private actions" in the development server debug output.
313
314   Hello, World! Using a View and a Template
315       In the Catalyst world a "View" itself is not a page of XHTML or a
316       template designed to present a page to a browser. Rather, it is the
317       module that determines the type of view -- HTML, PDF, XML, etc. For the
318       thing that generates the content of that view (such as a Template
319       Toolkit template file), the actual templates go under the "root"
320       directory.
321
322       To create a TT view, run:
323
324           $ script/hello_create.pl view HTML TT
325
326       This creates the lib/Hello/View/HTML.pm module, which is a subclass of
327       Catalyst::View::TT.
328
329       •   The "view" keyword tells the create script that you are creating a
330           view.
331
332       •   The first argument "HTML" tells the script to name the View module
333           "HTML.pm", which is a commonly used name for TT views.  You can
334           name it anything you want, such as "MyView.pm". If you have more
335           than one view, be sure to set the default_view in Hello.pm (See
336           Catalyst::View::TT for more details on setting this).
337
338       •   The final "TT" tells Catalyst the type of the view, with "TT"
339           indicating that you want to use a Template Toolkit view.
340
341       If you look at lib/Hello/View/HTML.pm you will find that it only
342       contains a config statement to set the TT extension to ".tt".
343
344       Now that the HTML.pm "View" exists, Catalyst will autodiscover it and
345       be able to use it to display the view templates using the "process"
346       method that it inherits from the Catalyst::View::TT class.
347
348       Template Toolkit is a very full-featured template facility, with
349       excellent documentation at <http://template-toolkit.org/>, but since
350       this is not a TT tutorial, we'll stick to only basic TT usage here (and
351       explore some of the more common TT features in later chapters of the
352       tutorial).
353
354       Create a root/hello.tt template file (put it in the "root" under the
355       "Hello" directory that is the base of your application). Here is a
356       simple sample:
357
358           <p>
359               This is a TT view template, called '[% template.name %]'.
360           </p>
361
362       [% and %] are markers for the TT parts of the template. Inside you can
363       access Perl variables and classes, and use TT directives. In this case,
364       we're using a special TT variable that defines the name of the template
365       file (hello.tt).  The rest of the template is normal HTML.
366
367       Change the hello method in lib/Hello/Controller/Root.pm to the
368       following:
369
370           sub hello :Global {
371               my ( $self, $c ) = @_;
372
373               $c->stash(template => 'hello.tt');
374           }
375
376       This time, instead of doing "$c->response->body()", you are setting the
377       value of the "template" hash key in the Catalyst "stash", an area for
378       putting information to share with other parts of your application. The
379       "template" key determines which template will be displayed at the end
380       of the request cycle. Catalyst controllers have a default "end" action
381       for all methods which causes the first (or default) view to be rendered
382       (unless there's a "$c->response->body()" statement). So your template
383       will be magically displayed at the end of your method.
384
385       After saving the file, the development server should automatically
386       restart (again, the tutorial is written to assume that you are using
387       the "-r" option -- manually restart it if you aren't), and look at
388       <http://localhost:3000/hello> in your web browser again. You should see
389       the template that you just created.
390
391       TIP: If you keep the server running with "-r" in a "background window,"
392       don't let that window get totally hidden... if you have a syntax error
393       in your code, the debug server output will contain the error
394       information.
395
396       Note: You will probably run into a variation of the "stash" statement
397       above that looks like:
398
399           $c->stash->{template} = 'hello.tt';
400
401       Although this style is still relatively common, the approach we used
402       previous is becoming more common because it allows you to set multiple
403       stash variables in one line.  For example:
404
405           $c->stash(template => 'hello.tt', foo => 'bar',
406                     another_thing => 1);
407
408       You can also set multiple stash values with a hashref:
409
410           $c->stash({template => 'hello.tt', foo => 'bar',
411                     another_thing => 1});
412
413       Any of these formats work, but the "$c->stash(name => value);" style is
414       growing in popularity -- you may wish to use it all the time (even when
415       you are only setting a single value).
416

CREATE A SIMPLE CONTROLLER AND AN ACTION

418       Create a controller named "Site" by executing the create script:
419
420           $ script/hello_create.pl controller Site
421
422       This will create a lib/Hello/Controller/Site.pm file (and a test file).
423       If you bring Site.pm up in your editor, you can see that there's not
424       much there to see.
425
426       In lib/Hello/Controller/Site.pm, add the following method:
427
428           sub test :Local {
429               my ( $self, $c ) = @_;
430
431               $c->stash(username => 'John',
432                         template => 'site/test.tt');
433           }
434
435       Notice the "Local" attribute on the "test" method. This will cause the
436       "test" action (now that we have assigned an "action type" to the method
437       it appears as a "controller action" to Catalyst) to be executed on the
438       "controller/method" URL, or, in this case, "site/test".  We will see
439       additional information on controller actions throughout the rest of the
440       tutorial, but if you are curious take a look at "Actions" in
441       Catalyst::Manual::Intro.
442
443       It's not actually necessary to set the template value as we do here.
444       By default TT will attempt to render a template that follows the naming
445       pattern "controller/method.tt", and we're following that pattern here.
446       However, in other situations you will need to specify the template
447       (such as if you've "forwarded" to the method, or if it doesn't follow
448       the default naming convention).
449
450       We've also put the variable "username" into the stash, for use in the
451       template.
452
453       Make a subdirectory "site" in the "root" directory.
454
455           $ mkdir root/site
456
457       Create a new template file in that directory named root/site/test.tt
458       and include a line like:
459
460           <p>Hello, [% username %]!</p>
461
462       Once the server automatically restarts, notice in the server output
463       that "/site/test" is listed in the Loaded Path actions.  Go to
464       <http://localhost:3000/site/test> in your browser and you should see
465       your test.tt file displayed, including the name "John" that you set in
466       the controller.
467
468       You can jump to the next chapter of the tutorial here: More Catalyst
469       Basics
470

AUTHORS

472       Gerda Shank, "gerda.shank@gmail.com" Kennedy Clark, "hkclark@gmail.com"
473
474       Feel free to contact the author for any errors or suggestions, but the
475       best way to report issues is via the CPAN RT Bug system at
476       <https://rt.cpan.org/Public/Dist/Display.html?Name=Catalyst-Manual>.
477
478       Copyright 2006-2011, Kennedy Clark, under the Creative Commons
479       Attribution Share-Alike License Version 3.0
480       (<https://creativecommons.org/licenses/by-sa/3.0/us/>).
481
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