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Catalyst::Manual::TutoUserCConlributednPerl:Document::03_MoreCatalystBasics(3)

NAME
       Catalyst::Manual::Tutorial::03_MoreCatalystBasics - Catalyst Tutorial -
       Chapter 3: More Catalyst	Application Development	Basics

OVERVIEW
       This is Chapter 3 of 10 for the Catalyst	tutorial.

       Tutorial	Overview

       1.  Introduction

       2.  Catalyst Basics

       3.  03_More Catalyst Basics

       4.  Basic CRUD

       5.  Authentication

       6.  Authorization

       7.  Debugging

       8.  Testing

       9.  Advanced CRUD

       10. Appendices

DESCRIPTION
       This chapter of the tutorial builds on the work done in Chapter 2 to
       explore some features that are more typical of "real world" web
       applications. From this chapter of the tutorial onward, we will be
       building	a simple book database application.  Although the application
       will be too limited to be of use	to anyone, it should provide a basic
       environment where we can	explore	a variety of features used in
       virtually all web applications.

       Source code for the tutorial in included	in the /home/catalyst/Final
       directory of the	Tutorial Virtual machine (one subdirectory per
       chapter).  There	are also instructions for downloading the code in
       Catalyst::Manual::Tutorial::01_Intro.

       Please take a look at "STARTING WITH THE	TUTORIAL VIRTUAL MACHINE" in
       Catalyst::Manual::Tutorial::01_Intro before doing the rest of this
       tutorial.  Although the tutorial	should work correctly under most any
       recent version of Perl running on any operating system, the tutorial
       has been	written	using the virtual machine that is available for
       download.  The entire tutorial has been tested to be sure it runs
       correctly in this environment, so it is the most	trouble-free way to
       get started with	Catalyst.

CREATE A NEW APPLICATION
       The remainder of	the tutorial will build	an application called "MyApp".
       First use the Catalyst catalyst.pl script to initialize the framework
       for the "MyApp" application (make sure you aren't still inside the
       directory of the	"Hello"	application from the previous chapter of the
       tutorial	or in a	directory that already has a "MyApp" subdirectory):

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

       And change the "MyApp" directory	the helper created:

	   $ cd	MyApp

       This creates a similar skeletal structure to what we saw	in Chapter 2
       of the tutorial,	except with "MyApp" and	"myapp"	substituted for
       "Hello" and "hello".  (As noted in Chapter 2, omit the ".pl" from the
       command if you are using	Strawberry Perl.)

EDIT THE LIST OF CATALYST PLUGINS
       One of the greatest benefits of Catalyst	is that	it has such a large
       library of base classes and plugins available that you can use to
       easily add functionality	to your	application. Plugins are used to
       seamlessly integrate existing Perl modules into the overall Catalyst
       framework. In general, they do this by adding additional	methods	to the
       "context" object	(generally written as $c) that Catalyst	passes to
       every component throughout the framework.

       Take a look at the file lib/MyApp.pm that the helper created above.  By
       default,	Catalyst enables three plugins/flags:

       o   "-Debug" Flag

	   Enables the Catalyst	debug output you saw when we started the
	   script/myapp_server.pl development server earlier.  You can remove
	   this	item when you place your application into production.

	   To be technically correct, it turns out that	"-Debug" is not	a
	   plugin, but a flag.	Although most of the items specified on	the
	   "use	Catalyst" line of your application class will be plugins,
	   Catalyst supports a limited number of flag options (of these,
	   "-Debug" is the most	common).  See the documentation	for
	   Catalyst.pm to get details on other flags (currently	"-Engine",
	   "-Home", "-Log", and	"-Stats").

	   If you prefer, there	are several other ways to enable debug output:

	   o   the "$c->debug" method on the $c	Catalyst context object

	   o   the "-d"	option on the script/myapp_server.pl script

	   o   the "CATALYST_DEBUG=1" environment variable (or
	       "CATALYST_DEBUG=0" to temporarily disable debug output)

	   TIP:	Depending on your needs, it can	be helpful to permanently
	   remove "-Debug" from	"lib/MyApp.pm" and then	use the	"-d" option to
	   script/myapp_server.pl to re-enable it when needed.	We will	not be
	   using that approach in the tutorial,	but feel free to make use of
	   it in your own projects.

       o   Catalyst::Plugin::ConfigLoader

	   "ConfigLoader" provides an automatic	way to load configurable
	   parameters for your application from	a central Config::General file
	   (versus having the values hard-coded	inside your Perl modules).
	   Config::General uses	syntax very similar to Apache configuration
	   files.  We will see how to use this feature of Catalyst during the
	   authentication and authorization sections (Chapter 5	and Chapter
	   6).

	   IMPORTANT NOTE: If you are using a version of Catalyst::Devel prior
	   to version 1.06, be aware that Catalyst changed the default format
	   from	YAML to	the more straightforward Config::General style.	 This
	   tutorial uses the newer "myapp.conf"	file for Config::General.
	   However, Catalyst supports both formats and will automatically use
	   either myapp.conf or	myapp.yml (or any other	format supported by
	   Catalyst::Plugin::ConfigLoader and Config::Any).  If	you are	using
	   a version of	Catalyst::Devel	prior to 1.06, you can convert to the
	   newer format	by simply creating the myapp.conf file manually	and
	   deleting myapp.yml.	The default contents of	the myapp.conf you
	   create should only consist of one line:

	       name MyApp

	   TIP:	This script can	be useful for converting between configuration
	   formats:

	       perl -Ilib -e 'use MyApp; use Config::General;
		   Config::General->new->save_file("myapp.conf", MyApp->config);'

       o   Catalyst::Plugin::Static::Simple

	   "Static::Simple" provides an	easy way to serve static content, such
	   as images and CSS files, from the development server.

       For our application, we want to add one new plugin to the mix.  To do
       this, edit lib/MyApp.pm (this file is generally referred	to as your
       application class) and delete the lines with:

	   use Catalyst	qw/
	       -Debug
	       ConfigLoader
	       Static::Simple
	   /;

       Then replace it with:

	   # Load plugins
	   use Catalyst	qw/
	       -Debug
	       ConfigLoader
	       Static::Simple

	       StackTrace
	   /;

       Note: Recent versions of	Catalyst::Devel	have used a variety of
       techniques to load these	plugins/flags.	For example, you might see the
       following:

	   __PACKAGE__->setup(qw/-Debug	ConfigLoader Static::Simple/);

       Don't let these variations confuse you -- they all accomplish the same
       result.

       This tells Catalyst to start using one additional plugin,
       Catalyst::Plugin::StackTrace, to	add a stack trace near the top of the
       standard	Catalyst "debug	screen"	(the screen Catalyst sends to your
       browser when an error occurs). Be aware that StackTrace output appears
       in your browser,	not in the console window from which you're running
       your application, which is where	logging	output usually goes.

       Make sure when adding new plugins you also include them as a new
       dependency within the Makefile.PL file. For example, after adding the
       StackTrace plugin the Makefile.PL should	include	the following line:

	   requires 'Catalyst::Plugin::StackTrace';

       Notes:

       o   "__PACKAGE__" is just a shorthand way of referencing	the name of
	   the package where it	is used.  Therefore, in	MyApp.pm,
	   "__PACKAGE__" is equivalent to "MyApp".

       o   You will want to disable StackTrace before you put your application
	   into	production, but	it can be helpful during development.

       o   When	specifying plugins, you	can omit "Catalyst::Plugin::" from the
	   name.  Additionally,	you can	spread the plugin names	across
	   multiple lines as shown here	or place them all on one line.

       o   If you want to see what the StackTrace error	screen looks like,
	   edit	lib/MyApp/Controller/Root.pm and put a "die "Oops";" command
	   in the "sub index :Path :Args(0)" method.  Then start the
	   development server and open "http://localhost:3000/"	in your
	   browser.  You should	get a screen that starts with "Caught
	   exception in	MyApp::Controller::Root->index"	with sections showing
	   a stacktrace, information about the Request and Response objects,
	   the stash (something	we will	learn about soon), and the
	   applications	configuration.	Just don't forget to remove the	die
	   before you continue the tutorial!  :-)

CREATE A CATALYST CONTROLLER
       As discussed earlier, controllers are where you write methods that
       interact	with user input.  Typically, controller	methods	respond	to
       "GET" and "POST"	requests from the user's web browser.

       Use the Catalyst	"create" script	to add a controller for	book-related
       actions:

	   $ script/myapp_create.pl controller Books
	    exists "/home/catalyst/MyApp/script/../lib/MyApp/Controller"
	    exists "/home/catalyst/MyApp/script/../t"
	   created "/home/catalyst/MyApp/script/../lib/MyApp/Controller/Books.pm"
	   created "/home/catalyst/MyApp/script/../t/controller_Books.t"

       Then edit lib/MyApp/Controller/Books.pm (as discussed in	Chapter	2 of
       the Tutorial, Catalyst has a separate directory under lib/MyApp for
       each of the three parts of MVC: "Model",	"View" and "Controller") and
       add the following method	to the controller:

	   =head2 list

	   Fetch all book objects and pass to books/list.tt2 in	stash to be displayed

	   =cut

	   sub list :Local {
	       # Retrieve the usual Perl OO '$self' for	this object. $c	is the Catalyst
	       # 'Context' that's used to 'glue	together' the various components
	       # that make up the application
	       my ($self, $c) =	@_;

	       # Retrieve all of the book records as book model	objects	and store in the
	       # stash where they can be accessed by the TT template
	       # $c->stash(books => [$c->model('DB::Book')->all]);
	       # But, for now, use this	code until we create the model later
	       $c->stash(books => '');

	       # Set the TT template to	use.  You will almost always want to do	this
	       # in your action	methods	(action	methods	respond	to user	input in
	       # your controllers).
	       $c->stash(template => 'books/list.tt2');
	   }

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

       Programmers experienced with object-oriented Perl should	recognize
       $self as	a reference to the object where	this method was	called.	 On
       the other hand, $c will be new to many Perl programmers who have	not
       used Catalyst before.  This is the "Catalyst Context object", and it is
       automatically passed as the second argument to all Catalyst action
       methods.	 It is used to pass information	between	components and provide
       access to Catalyst and plugin functionality.

       Catalyst	Controller actions are regular Perl methods, but they make use
       of attributes (the "":Local"" next to the ""sub list"" in the code
       above) to provide additional information	to the Catalyst	dispatcher
       logic (note that	there can be an	optional space between the colon and
       the attribute name; you will see	attributes written both	ways).	Most
       Catalyst	Controllers use	one of five action types:

       o   :Private -- Use ":Private" for methods that you want	to make	into
	   an action, but you do not want Catalyst to directly expose the
	   method to your users.  Catalyst will	not map	":Private" methods to
	   a URI.  Use them for	various	sorts of "special" methods (the
	   "begin", "auto", etc.  discussed below) or for methods you want to
	   be able to "forward"	or "detach" to.	 (If the method	is a "plain
	   old method" that you	don't want to be an action at all, then	just
	   define the method without any attribute -- you can call it in your
	   code, but the Catalyst dispatcher will ignore it.  You will also
	   have	to manually include $c if you want access to the context
	   object in the method	vs. having Catalyst automatically include $c
	   in the argument list	for you	if it's	a full-fledged action.)

	   There are five types	of "special" built-in ":Private" actions:
	   "begin", "end", "default", "index", and "auto".

	   o   With "begin", "end", "default", "index" private actions,	only
	       the most	specific action	of each	type will be called.  For
	       example,	if you define a	"begin"	action in your controller it
	       will override a "begin" action in your application/root
	       controller -- only the action in	your controller	will be
	       called.

	   o   Unlike the other	actions	where only a single method is called
	       for each	request, every auto action along the chain of
	       namespaces will be called.  Each	"auto" action will be called
	       from the	application/root controller down through the most
	       specific	class.

       o   :Path -- ":Path" actions let	you map	a method to an explicit	URI
	   path.  For example, "":Path('list')"" in
	   lib/MyApp/Controller/Books.pm would match on	the URL
	   "http://localhost:3000/books/list", but "":Path('/list')"" would
	   match on "http://localhost:3000/list" (because of the leading
	   slash).  You	can use	":Args()" to specify how many arguments	an
	   action should accept.  See "Action-types" in
	   Catalyst::Manual::Intro for more information	and examples.

       o   :Local -- ":Local" is merely	a shorthand for
	   "":Path('_name_of_method_')"".  For example,	these are equivalent:
	   ""sub create_book :Local {...}"" and	""sub create_book
	   :Path('create_book')	{...}"".

       o   :Global -- ":Global"	is merely a shorthand for
	   "":Path('/_name_of_method_')"".  For	example, these are equivalent:
	   ""sub create_book :Global {...}"" and ""sub create_book
	   :Path('/create_book') {...}"".

       o   :Chained -- Newer Catalyst applications tend	to use the Chained
	   dispatch form of action types because of its	power and flexibility.
	   It allows a series of controller methods to be automatically
	   dispatched when servicing a single user request.  See
	   Catalyst::Manual::Tutorial::04_BasicCRUD and
	   Catalyst::DispatchType::Chained for more information	on chained
	   actions.

       You should refer	to "Action-types" in Catalyst::Manual::Intro for
       additional information and for coverage of some lesser-used action
       types not discussed here	("Regex" and "LocalRegex").

CATALYST VIEWS
       As mentioned in Chapter 2 of the	tutorial, views	are where you render
       output, typically for display in	the user's web browser (but can
       generate	other types of output such as PDF or JSON).  The code in
       lib/MyApp/View selects the type of view to use, with the	actual
       rendering template found	in the "root" directory.  As with virtually
       every aspect of Catalyst, options abound	when it	comes to the specific
       view technology you adopt inside	your application. However, most
       Catalyst	applications use the Template Toolkit, known as	TT (for	more
       information on TT, see <http://www.template-toolkit.org>). Other
       somewhat	popular	view technologies include Mason
       (<http://www.masonhq.com> and
       <https://masonbook.houseabsolute.com/book/>) and	HTML::Template.

   Create a Catalyst View
       When using TT for the Catalyst view, the	main helper script is
       Catalyst::Helper::View::TT.  You	may also come across references	to
       Catalyst::Helper::View::TTSite, but its use is now deprecated.

       For our book application, enter the following command to	enable the
       "TT" style of view rendering:

	   $ script/myapp_create.pl view HTML TT
	    exists "/home/catalyst/MyApp/script/../lib/MyApp/View"
	    exists "/home/catalyst/MyApp/script/../t"
	    created "/home/catalyst/MyApp/script/../lib/MyApp/View/HTML.pm"
	    created "/home/catalyst/MyApp/script/../t/view_HTML.t"

       This creates a view called "HTML" (the first argument) in a file	called
       "HTML.pm" that uses Catalyst::View::TT (the second argument) as the
       "rendering engine".

       It is now up to you to decide how you want to structure your view
       layout.	For the	tutorial, we will start	with a very simple TT template
       to initially demonstrate	the concepts, but quickly migrate to a more
       typical "wrapper	page" type of configuration (where the "wrapper"
       controls	the overall "look and feel" of your site from a	single file or
       set of files).

       Edit lib/MyApp/View/HTML.pm and you should see something	similar	to the
       following:

	   __PACKAGE__->config(
	       TEMPLATE_EXTENSION => '.tt',
	       render_die => 1,
	   );

       And update it to	match:

	   __PACKAGE__->config(
	       # Change	default	TT extension
	       TEMPLATE_EXTENSION => '.tt2',
	       render_die => 1,
	   );

       This changes the	default	extension for Template Toolkit from '.tt' to
       '.tt2'.

       You can also configure components in your application class. For
       example,	Edit lib/MyApp.pm and you should see the default configuration
       above the call to "_PACKAGE__->setup" (your defaults could be different
       depending on the	version	of Catalyst you	are using):

	   __PACKAGE__->config(
	       name => 'MyApp',
	       # Disable deprecated behavior needed by old applications
	       disable_component_resolution_regex_fallback => 1,
	   );

       Change this to match the	following (insert a new	"__PACKAGE__->config"
       below the existing statement):

	   __PACKAGE__->config(
	       name => 'MyApp',
	       # Disable deprecated behavior needed by old applications
	       disable_component_resolution_regex_fallback => 1,
	   );
	   __PACKAGE__->config(
	       # Configure the view
	       'View::HTML' => {
		   #Set	the location for TT files
		   INCLUDE_PATH	=> [
		       __PACKAGE__->path_to( 'root', 'src' ),
		   ],
	       },
	   );

       This changes the	base directory for your	template files from "root" to
       root/src.

       Please stick with the settings above for	the duration of	the tutorial,
       but feel	free to	use whatever options you desire	in your	applications
       (as with	most things in Perl, there's more than one way to do it...).

       Note: We	will use root/src as the base directory	for our	template
       files, with a full naming convention of
       root/src/_controller_name_/_action_name_.tt2.  Another popular option
       is to use root/ as the base (with a full	filename pattern of
       root/_controller_name_/_action_name_.tt2).

   Create a TT Template	Page
       First create a directory	for book-related TT templates:

	   $ mkdir -p root/src/books

       Then create root/src/books/list.tt2 in your editor and enter:

	   [% #	This is	a TT comment. -%]

	   [%- # Provide a title -%]
	   [% META title = 'Book List' -%]

	   [% #	Note That the '-' at the beginning or end of TT	code  -%]
	   [% #	"chomps" the whitespace/newline	at that	end of the    -%]
	   [% #	output (use View Source	in browser to see the effect) -%]

	   [% #	Some basic HTML	with a loop to display books -%]
	   <table>
	   <tr><th>Title</th><th>Rating</th><th>Author(s)</th></tr>
	   [% #	Display	each book in a table row %]
	   [% FOREACH book IN books -%]
	     <tr>
	       <td>[% book.title %]</td>
	       <td>[% book.rating %]</td>
	       <td></td>
	     </tr>
	   [% END -%]
	   </table>

       As indicated by the inline comments above, the "META title" line	uses
       TT's META feature to provide a title to the "wrapper" that we will
       create later (and essentially does nothing at the moment). Meanwhile,
       the "FOREACH" loop iterates through each	"book" model object and	prints
       the "title" and "rating"	fields.

       The "[%"	and "%]" tags are used to delimit Template Toolkit code.  TT
       supports	a wide variety of directives for "calling" other files,
       looping,	conditional logic, etc.	 In general, TT	simplifies the usual
       range of	Perl operators down to the single dot (".") operator.  This
       applies to operations as	diverse	as method calls, hash lookups, and
       list index values (see Template::Manual::Variables for details and
       examples).  In addition to the usual Template::Toolkit module Pod
       documentation, you can access the TT manual at Template::Manual.

       TIP: While you can build	all sorts of complex logic into	your TT
       templates, you should in	general	keep the "code"	part of	your templates
       as simple as possible.  If you need more	complex	logic, create helper
       methods in your model that abstract out a set of	code into a single
       call from your TT template.  (Note that the same	is true	of your
       controller logic	as well	-- complex sections of code in your
       controllers should often	be pulled out and placed into your model
       objects.)  In Chapter 4 of the tutorial we will explore some extremely
       helpful and powerful features of	DBIx::Class that allow you to pull
       code out	of your	views and controllers and place	it where it rightfully
       belongs in a model class.

   Test	Run The	Application
       To test your work so far, first start the development server:

	   $ script/myapp_server.pl -r

       Then point your browser to <http://localhost:3000> and you should still
       get the Catalyst	welcome	page.  Next, change the	URL in your browser to
       <http://localhost:3000/books/list>.  If you have	everything working so
       far, you	should see a web page that displays nothing other than our
       column headers for "Title", "Rating", and "Author(s)" --	we will	not
       see any books until we get the database and model working below.

       If you run into problems	getting	your application to run	correctly, it
       might be	helpful	to refer to some of the	debugging techniques covered
       in the Debugging	chapter	of the tutorial.

CREATE A SQLITE	DATABASE
       In this step, we	make a text file with the required SQL commands	to
       create a	database table and load	some sample data.  We will use SQLite
       (<https://www.sqlite.org>), a popular database that is lightweight and
       easy to use. Be sure to get at least version 3. Open myapp01.sql	in
       your editor and enter:

	   --
	   -- Create a very simple database to hold book and author information
	   --
	   PRAGMA foreign_keys = ON;
	   CREATE TABLE	book (
		   id	       INTEGER PRIMARY KEY,
		   title       TEXT ,
		   rating      INTEGER
	   );
	   -- 'book_author' is a many-to-many join table between books & authors
	   CREATE TABLE	book_author (
		   book_id     INTEGER REFERENCES book(id) ON DELETE CASCADE ON	UPDATE CASCADE,
		   author_id   INTEGER REFERENCES author(id) ON	DELETE CASCADE ON UPDATE CASCADE,
		   PRIMARY KEY (book_id, author_id)
	   );
	   CREATE TABLE	author (
		   id	       INTEGER PRIMARY KEY,
		   first_name  TEXT,
		   last_name   TEXT
	   );
	   ---
	   --- Load some sample	data
	   ---
	   INSERT INTO book VALUES (1, 'CCSP SNRS Exam Certification Guide', 5);
	   INSERT INTO book VALUES (2, 'TCP/IP Illustrated, Volume 1', 5);
	   INSERT INTO book VALUES (3, 'Internetworking	with TCP/IP Vol.1', 4);
	   INSERT INTO book VALUES (4, 'Perl Cookbook',	5);
	   INSERT INTO book VALUES (5, 'Designing with Web Standards', 5);
	   INSERT INTO author VALUES (1, 'Greg', 'Bastien');
	   INSERT INTO author VALUES (2, 'Sara', 'Nasseh');
	   INSERT INTO author VALUES (3, 'Christian', 'Degu');
	   INSERT INTO author VALUES (4, 'Richard', 'Stevens');
	   INSERT INTO author VALUES (5, 'Douglas', 'Comer');
	   INSERT INTO author VALUES (6, 'Tom',	'Christiansen');
	   INSERT INTO author VALUES (7, 'Nathan', 'Torkington');
	   INSERT INTO author VALUES (8, 'Jeffrey', 'Zeldman');
	   INSERT INTO book_author VALUES (1, 1);
	   INSERT INTO book_author VALUES (1, 2);
	   INSERT INTO book_author VALUES (1, 3);
	   INSERT INTO book_author VALUES (2, 4);
	   INSERT INTO book_author VALUES (3, 5);
	   INSERT INTO book_author VALUES (4, 6);
	   INSERT INTO book_author VALUES (4, 7);
	   INSERT INTO book_author VALUES (5, 8);

       Then use	the following command to build a myapp.db SQLite database:

	   $ sqlite3 myapp.db <	myapp01.sql

       If you need to create the database more than once, you probably want to
       issue the "rm myapp.db" command to delete the database before you use
       the "sqlite3 myapp.db < myapp01.sql" command.

       Once the	myapp.db database file has been	created	and initialized, you
       can use the SQLite command line environment to do a quick dump of the
       database	contents:

	   $ sqlite3 myapp.db
	   SQLite version 3.7.3
	   Enter ".help" for instructions
	   Enter SQL statements	terminated with	a ";"
	   sqlite> select * from book;
	   1|CCSP SNRS Exam Certification Guide|5
	   2|TCP/IP Illustrated, Volume	1|5
	   3|Internetworking with TCP/IP Vol.1|4
	   4|Perl Cookbook|5
	   5|Designing with Web	Standards|5
	   sqlite> .q
	   $

       Or:

	   $ sqlite3 myapp.db "select *	from book"
	   1|CCSP SNRS Exam Certification Guide|5
	   2|TCP/IP Illustrated, Volume	1|5
	   3|Internetworking with TCP/IP Vol.1|4
	   4|Perl Cookbook|5
	   5|Designing with Web	Standards|5

       As with most other SQL tools, if	you are	using the full "interactive"
       environment you need to terminate your SQL commands with	a ";" (it's
       not required if you do a	single SQL statement on	the command line).
       Use ".q"	to exit	from SQLite from the SQLite interactive	mode and
       return to your OS command prompt.

       Please note that	here we	have chosen to use 'singular' table names.
       This is because the default inflection code for older versions of
       DBIx::Class::Schema::Loader does	NOT handle plurals. There has been
       much philosophical discussion on	whether	table names should be plural
       or singular.  There is no one correct answer, as	long as	one makes a
       choice and remains consistent with it. If you prefer plural table names
       (e.g.  you think	that they are easier to	read) then see the
       documentation in	"naming" in DBIx::Class::Schema::Loader::Base (version
       0.05 or greater).

       For using other databases, such as PostgreSQL or	MySQL, see Appendix 2.

DATABASE ACCESS	WITH DBIx::Class
       Catalyst	can be used with virtually any form of datastore available via
       Perl.  For example, Catalyst::Model::DBI	can be used to access
       databases through the traditional Perl DBI interface or you can use a
       model to	access files of	any type on the	filesystem.  However, most
       Catalyst	applications use some form of object-relational	mapping	(ORM)
       technology to create objects associated with tables in a	relational
       database, and Matt Trout's DBIx::Class (abbreviated as "DBIC") is the
       usual choice (this tutorial will	use DBIx::Class).

       Although	DBIx::Class has	included support for a "create=dynamic"	mode
       to automatically	read the database structure every time the application
       starts, its use is no longer recommended.  While	it can make for
       "flashy"	demos, the use of the "create=static" mode we use below	can be
       implemented just	as quickly and provides	many advantages	(such as the
       ability to add your own methods to the overall DBIC framework, a
       technique that we see in	Chapter	4).

   Create Static DBIx::Class Schema Files
       Note: If	you are	not following along in the Tutorial Virtual Machine,
       please be sure that you have version 1.27 or higher of DBD::SQLite and
       version 0.39 or higher of Catalyst::Model::DBIC::Schema.	 (The Tutorial
       VM already has versions that are	known to work.)	 You can get your
       currently installed version numbers with	the following commands.

	   $ perl -MCatalyst::Model::DBIC::Schema\ 999
	   $ perl -MDBD::SQLite\ 999

       Before you continue, make sure your myapp.db database file is in	the
       application's topmost directory.	Now use	the model helper with the
       "create=static" option to read the database with
       DBIx::Class::Schema::Loader and automatically build the required	files
       for us:

	   $ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema	\
	       create=static dbi:SQLite:myapp.db \
	       on_connect_do="PRAGMA foreign_keys = ON"
	    exists "/home/catalyst/MyApp/script/../lib/MyApp/Model"
	    exists "/home/catalyst/MyApp/script/../t"
	   Dumping manual schema for MyApp::Schema to directory	/home/catalyst/MyApp/script/../lib ...
	   Schema dump completed.
	   created "/home/catalyst/MyApp/script/../lib/MyApp/Model/DB.pm"
	   created "/home/catalyst/MyApp/script/../t/model_DB.t"

       Please note the '\' above.  Depending on	your environment, you might be
       able to cut and paste the text as shown or need to remove the '\'
       character to that the command is	all on a single	line.

       The script/myapp_create.pl command breaks down like this:

       o   "DB"	is the name of the model class to be created by	the helper in
	   the lib/MyApp/Model directory.

       o   "DBIC::Schema" is the type of the model to create.  This equates to
	   Catalyst::Model::DBIC::Schema, the standard way to use a DBIC-based
	   model inside	of Catalyst.

       o   "MyApp::Schema" is the name of the DBIC schema file written to
	   lib/MyApp/Schema.pm.

       o   "create=static" causes DBIx::Class::Schema::Loader to load the
	   schema as it	runs and then write that information out into
	   lib/MyApp/Schema.pm and files under the lib/MyApp/Schema directory.

       o   "dbi:SQLite:myapp.db" is the	standard DBI connect string for	use
	   with	SQLite.

       o   And finally,	the "on_connect_do" string requests that
	   DBIx::Class::Schema::Loader create foreign key relationships	for us
	   (this is not	needed for databases such as PostgreSQL	and MySQL, but
	   is required for SQLite). If you take	a look at
	   lib/MyApp/Model/DB.pm, you will see that the	SQLite pragma is
	   propagated to the Model, so that SQLite's recent (and optional)
	   foreign key enforcement is enabled at the start of every database
	   connection.

       If you look in the lib/MyApp/Schema.pm file, you	will find that it only
       contains	a call to the "load_namespaces"	method.	 You will also find
       that lib/MyApp contains a "Schema" subdirectory,	which then has a
       subdirectory called "Result".  This "Result" subdirectory then has
       files named according to	each of	the tables in our simple database
       (Author.pm, BookAuthor.pm, and Book.pm).	 These three files are called
       "Result Classes"	(or "ResultSource Classes") in DBIx::Class
       nomenclature. Although the Result Class files are named after tables in
       our database, the classes correspond to the row-level data that is
       returned	by DBIC	(more on this later, especially	in "EXPLORING THE
       POWER OF	DBIC" in Catalyst::Manual::Tutorial::04_BasicCRUD).

       The idea	with the Result	Source files created under
       lib/MyApp/Schema/Result by the "create=static" option is	to only	edit
       the files below the "# DO NOT MODIFY THIS OR ANYTHING ABOVE!"  warning.
       If you place all	of your	changes	below that point in the	file, you can
       regenerate the automatically created information	at the top of each
       file should your	database structure get updated.

       Also note the "flow" of the model information across the	various	files
       and directories.	 Catalyst will initially load the model	from
       lib/MyApp/Model/DB.pm.  This file contains a reference to
       lib/MyApp/Schema.pm, so that file is loaded next.  Finally, the call to
       "load_namespaces" in "Schema.pm"	will load each of the "Result Class"
       files from the lib/MyApp/Schema/Result subdirectory.  The final outcome
       is that Catalyst	will dynamically create	three table-specific Catalyst
       models every time the application starts	(you can see these three model
       files listed in the debug output	generated when you launch the
       application).

       Additionally, the lib/MyApp/Schema.pm model can easily be loaded
       outside of Catalyst, for	example, in command-line utilities and/or cron
       jobs. lib/MyApp/Model/DB.pm provides a very thin	"bridge" between
       Catalyst	and this external database model.  Once	you see	how we can add
       some powerful features to our DBIC model	in Chapter 4, the elegance of
       this approach will start	to become more obvious.

       NOTE: Older versions of Catalyst::Model::DBIC::Schema use the
       deprecated DBIx::Class "load_classes" technique instead of the newer
       "load_namespaces".  For new applications, please	try to use
       "load_namespaces" since it more easily supports a very useful DBIC
       technique called	"ResultSet Classes."  If you need to convert an
       existing	application from "load_classes"	to "load_namespaces," you can
       use this	process	to automate the	migration, but first make sure you
       have version 0.39 of Catalyst::Model::DBIC::Schema and
       DBIx::Class::Schema::Loader version 0.05000 or later.

	   $ # Re-run the helper to upgrade for	you
	   $ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema	\
	       create=static naming=current use_namespaces=1 \
	       dbi:SQLite:myapp.db \
	       on_connect_do="PRAGMA foreign_keys = ON"

ENABLE THE MODEL IN THE	CONTROLLER
       Open lib/MyApp/Controller/Books.pm and un-comment the model code	we
       left disabled earlier so	that your version matches the following	(un-
       comment the line	containing "[$c->model('DB::Book')->all]" and delete
       the next	2 lines):

	   =head2 list

	   Fetch all book objects and pass to books/list.tt2 in	stash to be displayed

	   =cut

	   sub list :Local {
	       # Retrieve the usual Perl OO '$self' for	this object. $c	is the Catalyst
	       # 'Context' that's used to 'glue	together' the various components
	       # that make up the application
	       my ($self, $c) =	@_;

	       # Retrieve all of the book records as book model	objects	and store
	       # in the	stash where they can be	accessed by the	TT template
	       $c->stash(books => [$c->model('DB::Book')->all]);

	       # Set the TT template to	use.  You will almost always want to do	this
	       # in your action	methods	(action	methods	respond	to user	input in
	       # your controllers).
	       $c->stash(template => 'books/list.tt2');
	   }

       TIP: You	may see	the "$c->model('DB::Book')" un-commented above written
       as "$c->model('DB')->resultset('Book')".	 The two are equivalent.
       Either way, "$c->model" returns a DBIx::Class::ResultSet	which handles
       queries against the database and	iterating over the set of results that
       is returned.

       We are using the	"->all"	to fetch all of	the books.  DBIC supports a
       wide variety of more advanced operations	to easily do things like
       filtering and sorting the results.  For example,	the following could be
       used to sort the	results	by descending title:

	   $c->model('DB::Book')->search({}, {order_by => 'title DESC'});

       Some other examples are provided	in "Complex WHERE clauses" in
       DBIx::Class::Manual::Cookbook, with additional information found	at
       "search"	in DBIx::Class::ResultSet, "Searching" in
       DBIx::Class::Manual::FAQ, DBIx::Class::Manual::Intro and
       Catalyst::Model::DBIC::Schema.

   Test	Run The	Application
       First, let's enable an environment variable that	causes DBIx::Class to
       dump the	SQL statements used to access the database.  This is a helpful
       trick when you are trying to debug your database-oriented code.	Press
       "Ctrl-C"	to break out of	the development	server and enter:

	   $ export DBIC_TRACE=1
	   $ script/myapp_server.pl -r

       This assumes you	are using bash as your shell --	adjust accordingly if
       you are using a different shell (for example, under tcsh, use "setenv
       DBIC_TRACE 1").

       NOTE: You can also set this in your code	using
       "$class->storage->debug(1);".  See DBIx::Class::Manual::Troubleshooting
       for details (including options to log to	a file instead of displaying
       to the Catalyst development server log).

       Then launch the Catalyst	development server.  The log output should
       display something like:

	   $ script/myapp_server.pl -r
	   [debug] Debug messages enabled
	   [debug] Statistics enabled
	   [debug] Loaded plugins:
	   .----------------------------------------------------------------------------.
	   | Catalyst::Plugin::ConfigLoader  0.30					|
	   | Catalyst::Plugin::StackTrace  0.11						|
	   '----------------------------------------------------------------------------'

	   [debug] Loaded dispatcher "Catalyst::Dispatcher"
	   [debug] Loaded engine "Catalyst::Engine"
	   [debug] Found home "/home/catalyst/MyApp"
	   [debug] Loaded Config "/home/catalyst/MyApp/myapp.conf"
	   [debug] Loaded components:
	   .-----------------------------------------------------------------+----------.
	   | Class							     | Type	|
	   +-----------------------------------------------------------------+----------+
	   | MyApp::Controller::Books					     | instance	|
	   | MyApp::Controller::Root					     | instance	|
	   | MyApp::Model::DB						     | instance	|
	   | MyApp::Model::DB::Author					     | class	|
	   | MyApp::Model::DB::Book					     | class	|
	   | MyApp::Model::DB::BookAuthor				     | class	|
	   | MyApp::View::HTML						     | instance	|
	   '-----------------------------------------------------------------+----------'

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

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

	   [info] MyApp	powered	by Catalyst 5.80020
	   HTTP::Server::PSGI: Accepting connections at	http://0:3000

       NOTE: Be	sure you run the script/myapp_server.pl	command	from the
       'base' directory	of your	application, not inside	the script directory
       itself or it will not be	able to	locate the myapp.db database file.
       You can use a fully qualified or	a relative path	to locate the database
       file, but we did	not specify that when we ran the model helper earlier.

       Some things you should note in the output above:

       o   Catalyst::Model::DBIC::Schema dynamically created three model
	   classes, one	to represent each of the three tables in our database
	   ("MyApp::Model::DB::Author",	"MyApp::Model::DB::BookAuthor",	and
	   "MyApp::Model::DB::Book").

       o   The "list" action in	our Books controller showed up with a path of
	   "/books/list".

       Point your browser to <http://localhost:3000> and you should still get
       the Catalyst welcome page.

       Next, to	view the book list, change the URL in your browser to
       <http://localhost:3000/books/list>. You should get a list of the	five
       books loaded by the myapp01.sql script above without any	formatting.
       The rating for each book	should appear on each row, but the "Author(s)"
       column will still be blank (we will fill	that in	later).

       Also notice in the output of the	script/myapp_server.pl that
       DBIx::Class used	the following SQL to retrieve the data:

	   SELECT me.id, me.title, me.rating FROM book me

       because we enabled DBIC_TRACE.

       You now have the	beginnings of a	simple but workable web	application.
       Continue	on to future sections and we will develop the application more
       fully.

CREATE A WRAPPER FOR THE VIEW
       When using TT, you can (and should) create a wrapper that will
       literally wrap content around each of your templates.  This is
       certainly useful	as you have one	main source for	changing things	that
       will appear across your entire site/application instead of having to
       edit many individual files.

   Configure HTML.pm For The Wrapper
       In order	to create a wrapper, you must first edit your TT view and tell
       it where	to find	your wrapper file.

       Edit your TT view in lib/MyApp/View/HTML.pm and change it to match the
       following:

	   __PACKAGE__->config(
	       # Change	default	TT extension
	       TEMPLATE_EXTENSION => '.tt2',
	       # Set the location for TT files
	       INCLUDE_PATH => [
		       MyApp->path_to( 'root', 'src' ),
		   ],
	       # Set to	1 for detailed timer stats in your HTML	as comments
	       TIMER		  => 0,
	       # This is your wrapper template located in the 'root/src'
	       WRAPPER => 'wrapper.tt2',
	   );

   Create the Wrapper Template File and	Stylesheet
       Next you	need to	set up your wrapper template.  Basically, you'll want
       to take the overall layout of your site and put it into this file.  For
       the tutorial, open root/src/wrapper.tt2 and input the following:

	   <?xml version="1.0" encoding="UTF-8"?>
	   <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0	Strict//EN" [%#
	       %]"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
	   <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
	   <head>
	   <title>[% template.title or "My Catalyst App!" %]</title>
	   <link rel="stylesheet" href="[% c.uri_for('/static/css/main.css') %]" />
	   </head>

	   <body>
	   <div	id="outer">
	   <div	id="header">
	       [%# Your	logo could go here -%]
	       <img src="[% c.uri_for('/static/images/btn_88x31_powered.png') %]" />
	       [%# Insert the page title -%]
	       <h1>[% template.title or	site.title %]</h1>
	   </div>

	   <div	id="bodyblock">
	   <div	id="menu">
	       Navigation:
	       <ul>
		   <li><a href="[% c.uri_for('/books/list') %]">Home</a></li>
		   <li><a href="[% c.uri_for('/')
		       %]" title="Catalyst Welcome Page">Welcome</a></li>
	       </ul>
	   </div><!-- end menu -->

	   <div	id="content">
	       [%# Status and error messages %]
	       <span class="message">[%	status_msg %]</span>
	       <span class="error">[% error_msg	%]</span>
	       [%# This	is where TT will stick all of your template's contents.	-%]
	       [% content %]
	   </div><!-- end content -->
	   </div><!-- end bodyblock -->

	   <div	id="footer">Copyright (c) your name goes here</div>
	   </div><!-- end outer	-->

	   </body>
	   </html>

       Notice the status and error message sections in the code	above:

	   <span class="status">[% status_msg %]</span>
	   <span class="error">[% error_msg %]</span>

       If we set either	message	in the Catalyst	stash (e.g.,
       "$c->stash->{status_msg}	= 'Request was successful!'") it will be
       displayed whenever any view used	by that	request	is rendered.  The
       "message" and "error" CSS styles	can be customized to suit your needs
       in the root/static/css/main.css file we create below.

       Notes:

       o   The Catalyst	stash only lasts for a single HTTP request.  If	you
	   need	to retain information across requests you can use
	   Catalyst::Plugin::Session (we will use Catalyst sessions in the
	   Authentication chapter of the tutorial).

       o   Although it is beyond the scope of this tutorial, you may wish to
	   use a JavaScript or AJAX tool such as jQuery
	   (<https://www.jquery.com>) or Dojo (<https://dojotoolkit.org/>).

       Create A	Basic Stylesheet

       First create a central location for stylesheets under the static
       directory:

	   $ mkdir root/static/css

       Then open the file root/static/css/main.css (the	file referenced	in the
       stylesheet href link of our wrapper above) and add the following
       content:

	   #header {
	       text-align: center;
	   }
	   #header h1 {
	       margin: 0;
	   }
	   #header img {
	       float: right;
	   }
	   #footer {
	       text-align: center;
	       font-style: italic;
	       padding-top: 20px;
	   }
	   #menu {
	       font-weight: bold;
	       background-color: #ddd;
	   }
	   #menu ul {
	       list-style: none;
	       float: left;
	       margin: 0;
	       padding:	0 0 50%	5px;
	       font-weight: normal;
	       background-color: #ddd;
	       width: 100px;
	   }
	   #content {
	       margin-left: 120px;
	   }
	   .message {
	       color: #390;
	   }
	   .error {
	       color: #f00;
	   }

       You may wish to check out a "CSS	Framework" like	Emastic
       (<http://code.google.com/p/emastic/>) as	a way to quickly provide lots
       of high-quality CSS functionality.

   Test	Run The	Application
       Hit "Reload" in your web	browser	and you	should now see a formatted
       version of our basic book list. (Again, the development server should
       have automatically restarted when you made changes to
       lib/MyApp/View/HTML.pm. If you are not using the	"-r" option, you will
       need to hit "Ctrl-C" and	manually restart it. Also note that the
       development server does NOT need	to restart for changes to the TT and
       static files we created and edited in the "root"	directory -- those
       updates are handled on a	per-request basis.)

       Although	our wrapper and	stylesheet are obviously very simple, you
       should see how it allows	us to control the overall look of an entire
       website from two	central	files. To add new pages	to the site, just
       provide a template that fills in	the "content" section of our wrapper
       template	-- the wrapper will provide the	overall	feel of	the page.

   Updating the	Generated DBIx::Class Result Class Files
       If you take a look at the Schema	files automatically generated by
       DBIx::Class::Schema::Loader, you	will see that it has already defined
       "has_many" and "belongs_to" relationships on each side of our foreign
       keys. For example, take a look at lib/MyApp/Schema/Result/Book.pm and
       notice the following code:

	   =head1 RELATIONS

	   =head2 book_authors

	   Type: has_many

	   Related object: L<MyApp::Schema::Result::BookAuthor>

	   =cut

	   __PACKAGE__->has_many(
	     "book_authors",
	     "MyApp::Schema::Result::BookAuthor",
	     { "foreign.book_id" => "self.id" },
	     { cascade_copy => 0, cascade_delete => 0 },
	   );

       Each "Book" "has_many" "book_authors", where "BookAuthor" is the	many-
       to-many table that allows each Book to have multiple Authors, and each
       Author to have multiple books.  The arguments to	"has_many" are:

       o   "book_authors" - The	name for this relationship.  DBIC will create
	   an accessor on the "Books" DBIC Row object with this	name.

       o   "MyApp::Schema::Result::BookAuthor" - The name of the DBIC model
	   class referenced by this "has_many" relationship.

       o   "foreign.book_id" - "book_id" is the	name of	the foreign key	column
	   in the foreign table	that points back to this table.

       o   "self.id" - "id" is the name	of the column in this table that is
	   referenced by the foreign key.

       See "has_many" in DBIx::Class::Relationship for additional information.
       Note that you might see a "hand coded" version of the "has_many"
       relationship above expressed as:

	   __PACKAGE__->has_many(
	     "book_authors",
	     "MyApp::Schema::Result::BookAuthor",
	     "book_id",
	   );

       Where the third argument	is simply the name of the column in the
       foreign table.  However,	the hashref syntax used	by
       DBIx::Class::Schema::Loader is more flexible (for example, it can
       handle "multi-column foreign keys").

       Note: If	you are	using older versions of	SQLite and related DBIC	tools,
       you will	need to	manually define	your "has_many"	and "belongs_to"
       relationships. We recommend upgrading to	the versions specified above.
       :-)

       Have a look at lib/MyApp/Schema/Result/BookAuthor.pm and	notice that
       there is	a "belongs_to" relationship defined that acts as the "mirror
       image" to the "has_many"	relationship we	just looked at above:

	   =head1 RELATIONS

	   =head2 book

	   Type: belongs_to

	   Related object: L<MyApp::Schema::Result::Book>

	   =cut

	   __PACKAGE__->belongs_to(
	     "book",
	     "MyApp::Schema::Result::Book",
	     { id => "book_id" },
	     { join_type => "LEFT", on_delete => "CASCADE", on_update => "CASCADE" },
	   );

       The arguments are similar, but see "belongs_to" in
       DBIx::Class::Relationship for the details.

       Although	recent versions	of SQLite and DBIx::Class::Schema::Loader
       automatically handle the	"has_many" and "belongs_to" relationships,
       "many_to_many" relationship bridges (not	technically a relationship)
       currently need to be manually inserted.	To add a "many_to_many"
       relationship bridge, first edit lib/MyApp/Schema/Result/Book.pm and add
       the following text below	the "# You can replace this text..."  comment:

	   # many_to_many():
	   #   args:
	   #	 1) Name of relationship bridge, DBIC will create accessor with	this name
	   #	 2) Name of has_many() relationship this many_to_many()	is shortcut for
	   #	 3) Name of belongs_to() relationship in model class of	has_many() above
	   #   You must	already	have the has_many() defined to use a many_to_many().
	   __PACKAGE__->many_to_many(authors =>	'book_authors',	'author');

       Note: Be	careful	to put this code above the "1;"	at the end of the
       file.  As with any Perl package,	we need	to end the last	line with a
       statement that evaluates	to "true".  This is customarily	done with "1;"
       on a line by itself.

       The "many_to_many" relationship bridge is optional, but it makes	it
       easier to map a book to its collection of authors.  Without it, we
       would have to "walk" through the	"book_author" table as in
       "$book->book_author->first->author->last_name" (we will see examples on
       how to use DBIx::Class objects in your code soon, but note that because
       "$book->book_author" can	return multiple	authors, we have to use
       "first" to display a single author).  "many_to_many" allows us to use
       the shorter "$book->author->first->last_name". Note that	you cannot
       define a	"many_to_many" relationship bridge without also	having the
       "has_many" relationship in place.

       Then edit lib/MyApp/Schema/Result/Author.pm and add the reverse
       "many_to_many" relationship bridge for "Author" as follows (again, be
       careful to put in above the "1;"	but below the "# DO NOT	MODIFY THIS OR
       ANYTHING	ABOVE!"	comment):

	   # many_to_many():
	   #   args:
	   #	 1) Name of relationship bridge, DBIC will create accessor with	this name
	   #	 2) Name of has_many() relationship this many_to_many()	is shortcut for
	   #	 3) Name of belongs_to() relationship in model class of	has_many() above
	   #   You must	already	have the has_many() defined to use a many_to_many().
	   __PACKAGE__->many_to_many(books => 'book_authors', 'book');

   Run The Application
       Run the Catalyst	development server script with the "DBIC_TRACE"	option
       (it might still be enabled from earlier in the tutorial,	but here is an
       alternate way to	specify	the trace option just in case):

	   $ DBIC_TRACE=1 script/myapp_server.pl -r

       Make sure that the application loads correctly and that you see the
       three dynamically created model classes (one for	each of	the Result
       Classes we created).

       Then hit	the URL	<http://localhost:3000/books/list> with	your browser
       and be sure that	the book list still displays correctly.

       Note: You will not see the authors yet because the view isn't taking
       advantage of these relationships. Read on to the	next section where we
       update the template to do that.

UPDATING THE VIEW
       Let's add a new column to our book list page that takes advantage of
       the relationship	information we manually	added to our schema files in
       the previous section.  Edit root/src/books/list.tt2 and replace the
       "empty" table cell ""<td></td>""	with the following:

	   ...
	   <td>
	     [%	# NOTE:	See Chapter 4 for a better way to do this!			-%]
	     [%	# First	initialize a TT	variable to hold a list.  Then use a TT	FOREACH	-%]
	     [%	# loop in 'side	effect notation' to load just the last names of	the	-%]
	     [%	# authors into the list. Note that the 'push' TT vmethod doesn't return	-%]
	     [%	# a value, so nothing will be printed here.  But, if you have something	-%]
	     [%	# in TT	that does return a value and you don't want it printed,	you	-%]
	     [%	# 1) assign it to a bogus value, or					-%]
	     [%	# 2) use the CALL keyword to call it and discard the return value.	-%]
	     [%	tt_authors = [ ];
		tt_authors.push(author.last_name) FOREACH author = book.authors	%]
	     [%	# Now use a TT 'virtual	method'	to display the author count in parens	-%]
	     [%	# Note the use of the TT filter	"| html" to escape dangerous characters	-%]
	     ([% tt_authors.size | html	%])
	     [%	# Use another TT vmethod to join & print the names & comma separators	-%]
	     [%	tt_authors.join(', ') |	html %]
	   </td>
	   ...

       IMPORTANT NOTE: Again, you should keep as much "logic code" as possible
       out of your views.  This	kind of	logic belongs in your model (the same
       goes for	controllers -- keep them as "thin" as possible and push	all of
       the "complicated	code" out to your model	objects).  Avoid code like you
       see in the previous example -- we are only using	it here	to show	some
       extra features in TT until we get to the	more advanced model features
       we will see in Chapter 4	(see "EXPLORING	THE POWER OF DBIC" in
       Catalyst::Manual::Tutorial::04_BasicCRUD).

       Then hit	"Reload" in your browser (note that you	don't need to reload
       the development server or use the "-r" option when updating TT
       templates) and you should now see the number of authors each book has
       along with a comma-separated list of the	authors' last names.  (If you
       didn't leave the	development server running from	the previous step, you
       will obviously need to start it before you can refresh your browser
       window.)

       If you are still	running	the development	server with "DBIC_TRACE"
       enabled,	you should also	now see	five more "SELECT" statements in the
       debug output (one for each book as the authors are being	retrieved by
       DBIx::Class):

	   SELECT me.id, me.title, me.rating FROM book me:
	   SELECT author.id, author.first_name,	author.last_name FROM book_author me
	   JOIN	author author ON author.id = me.author_id WHERE	( me.book_id = ? ): '1'
	   SELECT author.id, author.first_name,	author.last_name FROM book_author me
	   JOIN	author author ON author.id = me.author_id WHERE	( me.book_id = ? ): '2'
	   SELECT author.id, author.first_name,	author.last_name FROM book_author me
	   JOIN	author author ON author.id = me.author_id WHERE	( me.book_id = ? ): '3'
	   SELECT author.id, author.first_name,	author.last_name FROM book_author me
	   JOIN	author author ON author.id = me.author_id WHERE	( me.book_id = ? ): '4'
	   SELECT author.id, author.first_name,	author.last_name FROM book_author me
	   JOIN	author author ON author.id = me.author_id WHERE	( me.book_id = ? ): '5'

       Also note in root/src/books/list.tt2 that we are	using "| html",	a type
       of TT filter, to	escape characters such as < and	> to &lt; and &gt; and
       avoid various types of dangerous	hacks against your application.	 In a
       real application, you would probably want to put	"| html" at the	end of
       every field where a user	has control over the information that can
       appear in that field (and can therefore inject markup or	code if	you
       don't "neutralize" those	fields).  In addition to "| html", Template
       Toolkit has a variety of	other useful filters that can be found in the
       documentation for Template::Filters.  (While we are on the topic	of
       security	and escaping of	dangerous values, one of the advantages	of
       using tools like	DBIC for database access or HTML::FormFu for form
       management [see Chapter 9] is that they automatically handle most
       escaping	for you	and therefore dramatically increase the	security of
       your app.)

RUNNING	THE APPLICATION	FROM THE COMMAND LINE
       In some situations, it can be useful to run your	application and
       display a page without using a browser.	Catalyst lets you do this
       using the script/myapp_test.pl script.  Just supply the URL you wish to
       display and it will run that request through the	normal controller
       dispatch	logic and use the appropriate view to render the output
       (obviously, complex pages may dump a lot	of text	to your	terminal
       window).	 For example, if "Ctrl+C" out of the development server	and
       then type:

	   $ script/myapp_test.pl "/books/list"

       You should get the same text as if you visited
       <http://localhost:3000/books/list> with the normal development server
       and asked your browser to view the page source.	You can	even pipe this
       HTML text output	to a text-based	browser	using a	command	like:

	   $ script/myapp_test.pl "/books/list"	| lynx -stdin

       And you should see a fully rendered text-based view of your page.  (If
       you are following along in Debian 6, type "sudo aptitude	-y install
       lynx" to	install	lynx.)	If you do start	lynx, you can use the "Q" key
       to quit.

OPTIONAL INFORMATION
       NOTE: The rest of this chapter of the tutorial is optional.  You	can
       skip to Chapter 4, Basic	CRUD, if you wish.

   Using 'RenderView' for the Default View
       Once your controller logic has processed	the request from a user, it
       forwards	processing to your view	in order to generate the appropriate
       response	output.	 Catalyst uses Catalyst::Action::RenderView by default
       to automatically	perform	this operation.	 If you	look in
       lib/MyApp/Controller/Root.pm, you should	see the	empty definition for
       the "sub	end" method:

	   sub end : ActionClass('RenderView') {}

       The following bullet points provide a quick overview of the
       "RenderView" process:

       o   Root.pm is designed to hold application-wide	logic.

       o   At the end of a given user request, Catalyst	will call the most
	   specific "end" method that's	appropriate.  For example, if the
	   controller for a request has	an "end" method	defined, it will be
	   called.  However, if	the controller does not	define a controller-
	   specific "end" method, the "global" "end" method in Root.pm will be
	   called.

       o   Because the definition includes an "ActionClass" attribute, the
	   Catalyst::Action::RenderView	logic will be executed after any code
	   inside the definition of "sub end" is run.  See
	   Catalyst::Manual::Actions for more information on "ActionClass".

       o   Because "sub	end" is	empty, this effectively	just runs the default
	   logic in "RenderView".  However, you	can easily extend the
	   "RenderView"	logic by adding	your own code inside the empty method
	   body	("{}") created by the Catalyst Helpers when we first ran the
	   catalyst.pl to initialize our application.  See
	   Catalyst::Action::RenderView	for more detailed information on how
	   to extend "RenderView" in "sub end".

   RenderView's	"dump_info" Feature
       One of the nice features	of "RenderView"	is that	it automatically
       allows you to add "dump_info=1" to the end of any URL for your
       application and it will force the display of the	"exception dump"
       screen to the client browser.  You can try this out by pointing your
       browser to this URL:

	   http://localhost:3000/books/list?dump_info=1

       You should get a	page with the following	message	at the top:

	   Caught exception in MyApp::Controller::Root->end "Forced debug -
	   Scrubbed output at /usr/share/perl5/Catalyst/Action/RenderView.pm line 46."

       Along with a summary of your application's state	at the end of the
       processing for that request.  The "Stash" section should	show a
       summarized version of the DBIC book model objects.  If desired, you can
       adjust the summarization	logic (called "scrubbing" logic) -- see
       Catalyst::Action::RenderView for	details.

       Note that you shouldn't need to worry about "normal clients" using this
       technique to "reverse engineer" your application	-- "RenderView"	only
       supports	the "dump_info=1" feature when your application	is running in
       "-Debug"	mode (something	you won't do once you have your	application
       deployed	in production).

   Using The Default Template Name
       By default, "Catalyst::View::TT"	will look for a	template that uses the
       same name as your controller action, allowing you to save the step of
       manually	specifying the template	name in	each action.  For example,
       this would allow	us to remove the "$c->stash->{template}	=
       'books/list.tt2';" line of our "list" action in the Books controller.
       Open "lib/MyApp/Controller/Books.pm" in your editor and comment out
       this line to match the following	(only the "$c->stash->{template}" line
       has changed):

	   =head2 list

	   Fetch all book objects and pass to books/list.tt2 in	stash to be displayed

	   =cut

	   sub list :Local {
	       # Retrieve the usual Perl OO '$self' for	this object. $c	is the Catalyst
	       # 'Context' that's used to 'glue	together' the various components
	       # that make up the application
	       my ($self, $c) =	@_;

	       # Retrieve all of the book records as book model	objects	and store in the
	       # stash where they can be accessed by the TT template
	       $c->stash(books => [$c->model('DB::Book')->all]);

	       # Set the TT template to	use.  You will almost always want to do	this
	       # in your action	methods	(actions methods respond to user input in
	       # your controllers).
	       #$c->stash(template => 'books/list.tt2');
	   }

       You should now be able to access	the <http://localhost:3000/books/list>
       URL as before.

       NOTE: If	you use	the default template technique,	you will not be	able
       to use either the "$c->forward" or the "$c->detach" mechanisms (these
       are discussed in	Chapter	2 and Chapter 9	of the Tutorial).

       IMPORTANT: Make sure that you do	not skip the following section before
       continuing to the next chapter 4	Basic CRUD.

   Return To A Manually	Specified Template
       In order	to be able to use "$c->forward"	and "$c->detach" later in the
       tutorial, you should remove the comment from the	statement in "sub
       list" in	lib/MyApp/Controller/Books.pm:

	   $c->stash(template => 'books/list.tt2');

       Then delete the "TEMPLATE_EXTENSION" line in lib/MyApp/View/HTML.pm.

       Check the <http://localhost:3000/books/list> URL	in your	browser.  It
       should look the same manner as with earlier sections.

       You can jump to the next	chapter	of the tutorial	here: Basic CRUD

AUTHOR
       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>.

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

perl v5.32.1		  Catalyst::Manual::Tutorial::03_MoreCatalystBasics(3)

NAME | OVERVIEW | DESCRIPTION | CREATE A NEW APPLICATION | EDIT THE LIST OF CATALYST PLUGINS | CREATE A CATALYST CONTROLLER | CATALYST VIEWS | CREATE A SQLITE DATABASE | DATABASE ACCESS WITH DBIx::Class | ENABLE THE MODEL IN THE CONTROLLER | CREATE A WRAPPER FOR THE VIEW | UPDATING THE VIEW | RUNNING THE APPLICATION FROM THE COMMAND LINE | OPTIONAL INFORMATION | AUTHOR

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