light edits, mostly typo-like

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

=head1 NAME

Catalyst::Manual::Tutorial::MoreCatalystBasics - Catalyst Tutorial - Chapter 3: More Catalyst Application Development Basics


=head1 OVERVIEW

This is B<Chapter 3 of 10> for the Catalyst tutorial.

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

=over 4

=item 1

L<Introduction|Catalyst::Manual::Tutorial::Intro>

=item 2

L<Catalyst Basics|Catalyst::Manual::Tutorial::CatalystBasics>

=item 3

B<More Catalyst Basics>

=item 4

L<Basic CRUD|Catalyst::Manual::Tutorial::BasicCRUD>

=item 5

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

=item 6

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

=item 7

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

=item 8

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

=item 9

L<Advanced CRUD|Catalyst::Manual::Tutorial::AdvancedCRUD>

=item 10

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

=back


=head1 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.

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

Please take a look at 
L<Catalyst::Manual::Tutorial::Intro/CATALYST INSTALLATION> 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 Debian 5 and 
tested to be sure it runs correctly in this environment.  


=head1 CREATE A NEW APPLICATION

The remainder of the tutorial will build an application called C<MyApp>.
First use the Catalyst C<catalyst.pl> script to initialize the framework
for the C<MyApp> application (make sure you aren't still inside the
directory of the C<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"
    $ cd MyApp

This creates a similar skeletal structure to what we saw in Chapter 2 of
the tutorial, except with C<MyApp> and C<myapp> substituted for
C<Hello> and C<hello>.


=head1 EDIT THE LIST OF CATALYST PLUGINS

One of the greatest benefits of Catalyst is that it has such a large
library of plugins and base classes available.  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
C<context> object (generally written as C<$c>) that Catalyst passes to
every component throughout the framework.

By default, Catalyst enables three plugins/flags:

=over 4

=item *

C<-Debug> Flag

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

As you may have noticed, C<-Debug> is not a plugin, but a I<flag>. 
Although most of the items specified on the C<__PACKAGE__-E<gt>setup> 
line of your application class will be plugins, Catalyst supports a 
limited number of flag options (of these, C<-Debug> is the most 
common).  See the documentation for C<Catalyst.pm> to get details on 
other flags (currently C<-Engine>, C<-Home>, and C<-Log>).

If you prefer, you can use the C<$c-E<gt>debug> method to enable debug
messages.

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

=item *

L<Catalyst::Plugin::ConfigLoader|Catalyst::Plugin::ConfigLoader>

C<ConfigLoader> provides an automatic way to load configurable
parameters for your application from a central
L<Config::General|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).

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

    name MyApp

B<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);'

=item *

L<Catalyst::Plugin::Static::Simple|Catalyst::Plugin::Static::Simple>

C<Static::Simple> provides an easy method of serving static content such
as images and CSS files under the development server.

=back

For our application, we want to add one new plugin into the mix.  To 
do this, edit C<lib/MyApp.pm> (this file is generally referred to as 
your I<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
                /;

B<Note:> Recent versions of C<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 new plugin, 
L<Catalyst::Plugin::StackTrace|Catalyst::Plugin::StackTrace>, to add a 
stack trace to the standard Catalyst "debug screen" (the screen 
Catalyst sends to your browser when an error occurs). Be aware that 
L<StackTrace|Catalyst::Plugin::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.

B<Notes:> 

=over 4

=item *

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

=item *

You will want to disable L<StackTrace|Catalyst::Plugin::StackTrace> 
before you put your application into production, but it can be helpful 
during development.

=item *

When specifying plugins on the C<__PACKAGE__-E<gt>setup> line, you can 
omit C<Catalyst::Plugin::> from the name.  Additionally, you can 
spread the plugin names across multiple lines as shown here, or place 
them all on one (or more) lines as with the default configuration.

=back


=head1 CREATE A CATALYST CONTROLLER

As discussed earlier, controllers are where you write methods that
interact with user input.  Typically, controller methods respond to
C<GET> and C<POST> messages from the user's web browser.

Use the Catalyst C<create> script to add a controller for book-related
actions:

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

Then edit C<lib/MyApp/Controller/Books.pm> (as discussed in Chapter 2 of
the Tutorial, Catalyst has a separate directory under C<lib/MyApp> for
each of the three parts of MVC: C<Model>, C<View>, and C<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::Books')->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';
    }

B<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 
C<$self> as a reference to the object where this method was called. 
On the other hand, C<$c> will be new to many Perl programmers who have 
not used Catalyst before (it's sometimes written as C<$context>).  The 
Context object is automatically passed to all Catalyst components.  It 
is used to pass information between components and provide access to 
Catalyst and plugin functionality.

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

=over 4

=item *

B<:Private> -- Use C<:Private> for methods that you want to make into 
an action, but you do not want Catalyst to directly expose the action 
to your users.  Catalyst will not map C<:Private> methods to a URI. 
Use them for various sorts of "special" methods (the C<begin>, 
C<auto>, etc. discussed below) or for methods you want to be able to 
C<forward> or C<detach> to.  (If the method is a plain old "helper 
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.)

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

=over 4

=item *

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

=item *

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

=back

=item *

B<:Path> -- C<:Path> actions let you map a method to an explicit URI 
path.  For example, "C<:Path('list')>" in 
C<lib/MyApp/Controller/Books.pm> would match on the URL 
C<http://localhost:3000/books/list> but "C<:Path('/list')>" would match 
on C<http://localhost:3000/list>.  You can use C<:Args()> to specify 
how many arguments an action should except.  See 
L<Catalyst::Manual::Intro/Action_types> for more information and a few 
examples.

=item *

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

=item *

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

=item *

B<: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 automatically be dispatched
to service a single user request.  See 
L<Catalyst::Manual::Tutorial::BasicCRUD|Catalyst::Manual::Tutorial::BasicCRUD> 
and L<Catalyst::DispatchType::Chained|Catalyst::DispatchType::Chained> 
for more information on chained actions.

=back

You should refer to L<Catalyst::Manual::Intro/Action_types> for 
additional information and for coverage of some lesser-used action 
types not discussed here (C<Regex> and C<LocalRegex>).


=head1 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 also 
possibly using other display output-generation systems).  The code in 
C<lib/MyApp/View> selects the I<type> of view to use, with the actual 
rendering template found in the C<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 L<http://www.template-toolkit.org>). Other 
somewhat popular view technologies include Mason 
(L<http://www.masonhq.com> and L<http://www.masonbook.com>) and 
L<HTML::Template> (L<http://html-template.sourceforge.net>).


=head2 Create a Catalyst View

When using TT for the Catalyst view, there are two main helper scripts:

=over 4

=item *

L<Catalyst::Helper::View::TT|Catalyst::Helper::View::TT>

=item *

L<Catalyst::Helper::View::TTSite|Catalyst::Helper::View::TTSite>

=back

Both helpers are similar. C<TT> creates the C<lib/MyApp/View/TT.pm>
file and leaves the creation of any hierarchical template organization
entirely up to you. (It also creates a C<t/view_TT.t> file for testing;
test cases will be discussed in Chapter 8.) C<TTSite>, on the other hand, 
creates a modular and hierarchical view layout with
separate Template Toolkit (TT) files for common header and footer
information, configuration values, a CSS stylesheet, and more.

While C<TTSite> was useful to bootstrap a project, its use is now
deprecated and to be considered historical.  For most Catalyst
applications it adds redundant functionality and structure; many in the
Catalyst community recommend that it's easier to learn both Catalyst and
Template Toolkit if you use the more basic C<TT> approach.
Consequently, this tutorial will use "plain old TT."

Enter the following command to enable the C<TT> style of view
rendering for this tutorial:

    $ script/myapp_create.pl view TT TT
     exists "/home/me/MyApp/script/../lib/MyApp/View"
     exists "/home/me/MyApp/script/../t"
     created "/home/me/MyApp/script/../lib/MyApp/View/TT.pm"
     created "/home/me/MyApp/script/../t/view_TT.t"

This simply creates a view called C<TT> (the second 'TT' argument) in 
a file called C<TT.pm> (the first 'TT' argument). 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 C<lib/MyApp/View/TT.pm> and you should see that the default
contents contains something similar to the following:

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

And update it to match:

    __PACKAGE__->config(
        # Change default TT extension
        TEMPLATE_EXTENSION => '.tt2',
        # Set the location for TT files
        INCLUDE_PATH => [
                MyApp->path_to( 'root', 'src' ),
            ],
    );

B<NOTE:> Make sure to add a comma after '.tt2' outside the single
quote.

This changes the default extension for Template Toolkit from '.tt' to
'.tt2' and changes the base directory for your template files from
C<root> to C<root/src>.  These changes from the default are done mostly
to facilitate the application we're developing in this tutorial; as with
most things Perl, there's more than one way to do it...

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


=head2 Create a TT Template Page

First create a directory for book-related TT templates:

    $ mkdir -p root/src/books

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

    [% # This is a TT comment.  The '-' at the end "chomps" the newline.  You won't -%]
    [% # see this "chomping" in your browser because HTML ignores blank lines, but  -%]
    [% # it WILL eliminate a blank line if you view the HTML source.  It's purely   -%]
    [%- # optional, but both the beginning and the ending TT tags support chomping. -%]
    
    [% # Provide a title -%]
    [% META title = 'Book List' -%]
    
    <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>
      </tr>
    [% END -%]
    </table>

As indicated by the inline comments above, the C<META title> line uses
TT's META feature to provide a title to the "wrapper" that we will
create later. Meanwhile, the C<FOREACH> loop iterates through each
C<book> model object and prints the C<title> and C<rating> fields.

If you are new to TT, the C<[%> and C<%]> tags are used to delimit TT
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 (C<.>) operator.
This applies to operations as diverse as method calls, hash lookups, and
list index values (see
L<http://search.cpan.org/perldoc?Template::Manual::Variables>
for details and examples).  In addition to the usual C<Template> module
Pod documentation, you can access the TT manual at
L<http://search.cpan.org/perldoc?Template::Manual>.

B<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.)


=head2 Test Run The Application

To test your work so far, first start the development server:

    $ script/myapp_server.pl

Then point your browser to L<http://localhost:3000> and you should
still get the Catalyst welcome page.  Next, change the URL in your
browser to L<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 L<Debugging|Catalyst::Manual::Tutorial::Debugging> part of the
tutorial.


=head1 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,
a popular database that is lightweight and easy to use.  Open
C<myapp01.sql> in your editor and enter:

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

Then use the following command to build a C<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 C<rm myapp.db> command to delete the database before you use
the C<sqlite3 myapp.db E<lt> myapp01.sql> command.

Once the C<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 3.5.9
    Enter ".help" for instructions
    sqlite> select * from books;
    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 books"
    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.

For using other databases, such as PostgreSQL or MySQL, see 
L<Appendix 2|Catalyst::Manual::Tutorial::Appendices>.


=head1 DATABASE ACCESS WITH DBIx::Class

Catalyst can be used with virtually any form of persistent datastore 
available via Perl.  For example, 
L<Catalyst::Model::DBI|Catalyst::Model::DBI> can be used to easily 
access databases through the traditional Perl C<DBI> interface. However, 
most Catalyst applications use some form of ORM technology to 
automatically create and save model objects as they are used.  Although 
L<Class::DBI|Class::DBI> has been a popular choice in the past, Matt 
Trout's L<DBIx::Class|DBIx::Class> (abbreviated as "DBIC") has rapidly 
emerged as the Perl-based ORM technology of choice. Most new Catalyst 
applications rely on DBIC, as will this tutorial.


=head2 Create a Dynamic DBIC Model

Use the C<create=dynamic> model helper option to build a model that
dynamically reads your database structure every time the application
starts:

    $ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema \
        create=dynamic dbi:SQLite:myapp.db
     exists "/home/me/MyApp/script/../lib/MyApp/Model"
     exists "/home/me/MyApp/script/../t"
     exists "/home/me/MyApp/script/../lib/MyApp"
    created "/home/me/MyApp/script/../lib/MyApp/Schema.pm"
    created "/home/me/MyApp/script/../lib/MyApp/Model/DB.pm"
    created "/home/me/MyApp/script/../t/model_DB.t"


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

=over 4

=item *

C<DB> is the name of the model class to be created by the helper in 
C<lib/MyApp/Model>.

=item *

C<DBIC::Schema> is the type of the model to create.

=item *

C<MyApp::Schema> is the name of the DBIC schema file written to
C<lib/MyApp/Schema.pm>.

=item *

Because we specified C<create=dynamic> to the helper, it use 
L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to 
dynamically load the schema information from the database every time 
the application starts.

=item *

And finally, C<dbi:SQLite:myapp.db> is the standard DBI connect string 
for use with SQLite.

=back

B<NOTE:> Although the C<create=dynamic> option to the DBIC helper
makes for a nifty demonstration, is only really suitable for very
small applications. After this demonstration, you should almost always
use the C<create=static> option that we switch to below.


=head1 ENABLE THE MODEL IN THE CONTROLLER

Open C<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<[$c-E<gt>model('DB::Books')-E<gt>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::Books')->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';
    }

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

We are using the C<-E<gt>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::Books')->search({}, {order_by => 'title DESC'});

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


=head2 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:

    $ export DBIC_TRACE=1

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

B<NOTE:> You can also set this in your code using
C<$class-E<gt>storage-E<gt>debug(1);>.  See
L<DBIx::Class::Manual::Troubleshooting> for details (including options
to log to 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
    [debug] Debug messages enabled
    [debug] Statistics enabled
    [debug] Loaded plugins:
    .----------------------------------------------------------------------------.
    | Catalyst::Plugin::ConfigLoader  0.20                                       |
    | Catalyst::Plugin::StackTrace  0.08                                         |
    | Catalyst::Plugin::Static::Simple  0.20                                     |
    '----------------------------------------------------------------------------'
    
    [debug] Loaded dispatcher "Catalyst::Dispatcher"
    [debug] Loaded engine "Catalyst::Engine::HTTP"
    [debug] Found home "/home/me/MyApp"
    [debug] Loaded Config "/home/me/MyApp/myapp.conf"
    [debug] Loaded components:
    .-----------------------------------------------------------------+----------.
    | Class                                                           | Type     |
    +-----------------------------------------------------------------+----------+
    | MyApp::Controller::Books                                        | instance |
    | MyApp::Controller::Root                                         | instance |
    | MyApp::Model::DB                                                | instance |
    | MyApp::Model::DB::Authors                                       | class    |
    | MyApp::Model::DB::BookAuthors                                   | class    |
    | MyApp::Model::DB::Books                                         | class    |
    | MyApp::View::TT                                                 | 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 5.71000
    You can connect to your server at http://debian:3000

B<NOTE:> Be sure you run the C<script/myapp_server.pl> command from
the 'base' directory of your application, not inside the C<script>
directory itself or it will not be able to locate the C<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:

=over 4

=item *

Catalyst::Model::DBIC::Schema dynamically created three model classes,
one to represent each of the three tables in our database
(C<MyApp::Model::DB::Authors>, C<MyApp::Model::DB::BookAuthors>,
and C<MyApp::Model::DB::Books>).

=item *

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

=back

Point your browser to L<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
L<http://localhost:3000/books/list>. You should get a list of the five
books loaded by the C<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 C<script/myapp_server.pl> that DBIC
used the following SQL to retrieve the data:

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


=head1 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.


=head2 Configure TT.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. Your TT view is located in
C<lib/MyApp/View/TT.pm>.

Edit C<lib/MyApp/View/TT.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',
    );


=head2 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 C<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<$c-E<gt>stash-E<gt>{status_msg} = 'Request was successful!'>) it
will be displayed whenever any view used by that request is rendered.
The C<message> and C<error> CSS styles can be customized to suit your
needs in the C<root/static/css/main.css> file we create below.

B<Notes:> 

=over 4

=item *

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

=item *

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

=back


=head3 Create A Basic Stylesheet

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

    $ mkdir root/static/css

Then open the file C<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
(L<http://code.google.com/p/emastic/>) as a way to quickly
provide lots of high-quality CSS functionality.


=head2 Test Run The Application

Restart the development server and hit "Reload" in your web browser
and you should now see a formatted version of our basic book list.
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 C<content> section of our wrapper
template -- the wrapper will provide the overall feel of the page.


=head1 A STATIC DATABASE MODEL WITH DBIx::Class

First, let's be sure we have a recent versino of the DBIC helper,
L<Catalyst::Model::DBIC::Schema|Catalyst::Model::DBIC::Schema>, by
running this command:

    $ perl -MCatalyst::Model::DBIC::Schema -e \
        'print "$Catalyst::Model::DBIC::Schema::VERSION\n"'
    0.23

If you don't have version 0.23 or higher, please run this command
to install it directly from CPAN:

    $ sudo cpan Catalyst::Model::DBIC::Schema

And re-run the version print command to verify that you are now at 
0.23 or higher.


=head2 Create Static DBIC Schema Files

Unlike the previous DBIC section where we had C<create=dynamic>
automatically discover the structure of the database every time the
application started, here we will use static schema files for more
control.  This is typical of most "real world" applications.

One option would be to manually create a separate schema file for each 
table in the database, however, lets use the same 
L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> used 
earlier with C<create=dynamic> to build the static files for us. 
First, lets remove the schema file created earlier:

    $ rm lib/MyApp/Schema.pm

Now regenerate the schema using the C<create=static> option:

    $ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema \
        create=static components=TimeStamp dbi:SQLite:myapp.db
     exists "/home/me/MyApp/script/../lib/MyApp/Model"
     exists "/home/me/MyApp/script/../t"
    Dumping manual schema for MyApp::Schema to directory /home/me/MyApp/script/../lib ...
    Schema dump completed.
     exists "/home/me/MyApp/script/../lib/MyApp/Model/DB.pm"

We could have also deleted C<lib/MyApp/Model/DB.pm>, but it would
have regenerated the same file (note the C<exists> in the output above).
If you take a look at C<lib/MyApp/Model/DB.pm>, it simply contains
a reference to the actual schema file in C<lib/MyApp/Schema.pm>
along with the database connect string.

If you look in the C<lib/MyApp/Schema.pm> file, you will find that it 
is no longer using 
L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> as its base 
class (L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> is 
only being used by the helper to load the schema once and then create 
the static files for us) and C<Schema.pm> only contains a call to the 
C<load_namespaces> method.  You will also find that C<lib/MyApp> 
contains a C<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 (C<Authors.pm>, 
C<BookAuthors.pm>, and C<Books.pm>).  These three files are called 
"Result Classes" in DBIC nomenclature. Although the Result Class files 
are named after tables in our database, the classes correspond to the 
I<row-level data> that is returned by DBIC (more on this later, 
especially in 
L<Catalyst::Manual::Tutorial::BasicCRUD/EXPLORING THE POWER OF DBIC>.

The idea with the Result Source files created under 
C<lib/MyApp/Schema/Result> by the C<create=static> option is to only 
edit the files below the C<# 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 
C<lib/MyApp/Model/DB.pm>.  This file contains a reference to 
C<lib/MyApp/Schema.pm>, so that file is loaded next.  Finally, the 
call to C<load_namespaces> in C<Schema.pm> will load each of the 
"Result Class" files from the C<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).

B<NOTE:> Older versions of 
L<Catalyst::Model::DBIC::Schema|Catalyst::Model::DBIC::Schema> use the 
deprecated DBIC C<load_classes> technique instead of the newer 
C<load_namspaces>.  For new applications, please try to use 
C<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 v0.23 C<Catalyst::Model::DBIC::Schema> as discussed above):

    $ # First delete the existing schema file to disable "compatibility" mode
    $ rm lib/MyApp/Schema.pm
    $
    $ # Then re-run the helper to build the files for "load_namespaces"
    $ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema \
        create=static components=TimeStamp dbi:SQLite:myapp.db
    $
    $ # Now convert the existing files over
    $ cd lib/MyApp/Schema
    $ perl -MIO::All -e 'for (@ARGV) { my $s < io($_); $s =~ s/.*\n\# You can replace.*?\n//s;
          $s =~ s/'MyApp::Schema::/'MyApp::Schema::Result::/g; my $d < io("Result/$_");
          $d =~ s/1;\n?//; "$d$s" > io("Result/$_"); }' *.pm
    $ cd ../../..
    $
    $ # And finally delete the old files
    $ rm lib/MyApp/Schema/*.pm

The "C<perl -MIO::ALL ...>" script will copy all the customized 
relationship (and other) information below "C<# DO NOT MODIFY>" line 
from the old files in C<lib/MyApp/Schema> to the new files in 
C<lib/MyApp/Schema/Result> (we will be starting to add some 
"customized relationship information in the section below).


=head2 Updating the Generated DBIC Result Class Files

Let's manually add some relationship information to the auto-generated 
Result Class files. (Note: if you are using a database other than 
SQLite, such as PostgreSQL, then the relationship could have been 
automatically placed in the Result Class files.  If so, you can skip 
this step.)  First edit C<lib/MyApp/Schema/Result/Books.pm> and add the 
following text below the C<# You can replace this text...> comment:

    #
    # Set relationships:
    #
    
    # has_many():
    #   args:
    #     1) Name of relationship, DBIC will create accessor with this name
    #     2) Name of the model class referenced by this relationship
    #     3) Column name in *foreign* table (aka, foreign key in peer table)
    __PACKAGE__->has_many(book_authors => 'MyApp::Schema::Result::BookAuthors', 'book_id');
    
    # many_to_many():
    #   args:
    #     1) Name of relationship, 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');


B<Note:> Be careful to put this code I<above> the C<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 C<true>.  This is customarily done with
C<1;> on a line by itself.

C<Important Note:> Although this tutorial uses plural names for both 
the names of the SQL tables and therefore the Result Classes (after 
all, C<Schema::Loader> automatically named the Result Classes from the 
names of the SQL tables it found), DBIC users prefer singular names 
for these items.  B<Please try to use singular table and DBIC 
model/Result Class names in your applications.>  This tutorial will 
migrate to singular names as soon as possible (patches welcomed). 
B<Note that while singular is preferred for the DBIC model, plural is 
perfectly acceptable for the names of the controller classes.>  After 
all, the C<Books.pm> controller operates on multiple books.

This code defines both a C<has_many> and a C<many_to_many> relationship.
The C<many_to_many> relationship is optional, but it makes it easier to
map a book to its collection of authors.  Without it, we would have to
"walk" though the C<book_authors> table as in 
C<$book-E<gt>book_authors-E<gt>first-E<gt>author-E<gt>last_name> 
(we will see examples on how to use DBIC objects in your code soon, 
but note that because C<$book-E<gt>book_authors> can return multiple 
authors, we have to use C<first> to display a single author). 
C<many_to_many> allows us to use the shorter 
C<$book-E<gt>authors-E<gt>first-E<gt>last_name>. 
Note that you cannot define a C<many_to_many> relationship without 
also having the C<has_many> relationship in place.

Then edit C<lib/MyApp/Schema/Result/Authors.pm> and add relationship
information as follows (again, be careful to put in above the C<1;> but
below the C<# DO NOT MODIFY THIS OR ANYTHING ABOVE!> comment):

    #
    # Set relationships:
    #
    
    # has_many():
    #   args:
    #     1) Name of relationship, DBIC will create accessor with this name
    #     2) Name of the model class referenced by this relationship
    #     3) Column name in *foreign* table (aka, foreign key in peer table)
    __PACKAGE__->has_many(book_author => 'MyApp::Schema::Result::BookAuthors', 'author_id');
    
    # many_to_many():
    #   args:
    #     1) Name of relationship, 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_author', 'book');

Finally, do the same for the "join table,"
C<lib/MyApp/Schema/Result/BookAuthors.pm>:

    #
    # Set relationships:
    #
    
    # belongs_to():
    #   args:
    #     1) Name of relationship, DBIC will create accessor with this name
    #     2) Name of the model class referenced by this relationship
    #     3) Column name in *this* table
    __PACKAGE__->belongs_to(book => 'MyApp::Schema::Result::Books', 'book_id');
    
    # belongs_to():
    #   args:
    #     1) Name of relationship, DBIC will create accessor with this name
    #     2) Name of the model class referenced by this relationship
    #     3) Column name in *this* table
    __PACKAGE__->belongs_to(author => 'MyApp::Schema::Result::Authors', 'author_id');


=head2 Run The Application

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

    $ DBIC_TRACE=1 script/myapp_server.pl

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

Then hit the URL L<http://localhost:3000/books/list> with your browser 
and be sure that the book list is displayed via the relationships 
established above. You can leave the development server running for 
the next step if you wish.

B<Note:> You will not see the authors yet because the view does not yet 
use the new relations. Read on to the next section where we update the 
template to do that.


=head1 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 C<root/src/books/list.tt2> add add the 
following code below the existing table cell that contains 
C<book.rating> (IOW, add a new table cell below the existing two 
C<E<lt>tdE<gt>> tags but above the closing C<E<lt>/trE<gt>> and 
C<E<lt>/tableE<gt>> tags):

    ...
    <td>
      [% # 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 does not print -%]
      [% # a value, so nothing will be printed here.  But, if you have something -%]
      [% # in TT that does return a method and you don't want it printed, you    -%]
      [% # can: 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>
    ...

Then hit "Reload" in your browser (note that you don't need to reload 
the development server or use the C<-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 C<DBIC_TRACE>
enabled, you should also now see five more C<SELECT> statements in the
debug output (one for each book as the authors are being retrieved by
DBIC):

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

Also note in C<root/src/books/list.tt2> that we are using "| html", a 
type of TT filter, to escape characters such as E<lt> and E<gt> 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 found in the documentation for 
L<Template::Filters|Template::Filters>.


=head1 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 C<scripts/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 you type:

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

You should get the same text as if you visited
L<http://localhost:3000/books/list> with the normal development server
and asked your browser to view the page source.


=head1 OPTIONAL INFORMATION

B<NOTE: The rest of this chapter of the tutorial is optional.  You can
skip to Chapter 4, L<Basic CRUD|Catalyst::Manual::Tutorial::BasicCRUD>,
if you wish.>


=head2 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
L<Catalyst::Action::RenderView|Catalyst::Action::RenderView> by
default to automatically performs this operation.  If you look in
C<lib/MyApp/Controller/Root.pm>, you should see the empty
definition for the C<sub end> method:

    sub end : ActionClass('RenderView') {}

The following bullet points provide a quick overview of the
C<RenderView> process:

=over 4

=item *

C<Root.pm> is designed to hold application-wide logic.

=item *

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

=item *

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

=item *

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

=back


=head2 Using The Default Template Name

By default, C<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<$c-E<gt>stash-E<gt>{template} = 'books/list.tt2';> line of our
C<list> action in the Books controller.  Open
C<lib/MyApp/Controller/Books.pm> in your editor and comment out this line
to match the following (only the C<$c-E<gt>stash-E<gt>{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::Books')->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 restart the development server as per the
previous section and access the L<http://localhost:3000/books/list>
as before.

B<NOTE:> Please note that if you use the default template technique,
you will B<not> be able to use either the C<$c-E<gt>forward> or
the C<$c-E<gt>detach> mechanisms (these are discussed in Chapter 2 and
Chapter 9 of the Tutorial).


=head2 Return To A Manually-Specified Template

In order to be able to use C<$c-E<gt>forward> and C<$c-E<gt>detach>
later in the tutorial, you should remove the comment from the
statement in C<sub list> in C<lib/MyApp/Controller/Books.pm>:

    $c->stash->{template} = 'books/list.tt2';

Then delete the C<TEMPLATE_EXTENSION> line in
C<lib/MyApp/View/TT.pm>.

You should then be able to restart the development server and
access L<http://localhost:3000/books/list> in the same manner as
with earlier sections.


=head1 AUTHOR

Kennedy Clark, C<hkclark@gmail.com>

Please report any errors, issues or suggestions to the author.  The
most recent version of the Catalyst Tutorial can be found at
L<http://dev.catalyst.perl.org/repos/Catalyst/Catalyst-Manual/5.70/trunk/lib/Catalyst/Manual/Tutorial/>.

Copyright 2006-2008, Kennedy Clark, under Creative Commons License
(L<http://creativecommons.org/licenses/by-sa/3.0/us/>).