=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 check out 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 way to serve static content, such
as images and CSS files, from 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> requests 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
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 accept. 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 be automatically 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 into output-generation systems, such as PDF or JSON).
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 it should 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>
<td></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.
The C<[%> and C<%]> 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 (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 datastore available
via Perl. For example, L<Catalyst::Model::DBI|Catalyst::Model::DBI>
can be used to access databases through the traditional Perl C<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. 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 DBIx::Class, as will this tutorial.
Although DBIx::Class has included support for a C<create=dynamic> mode
to automatically read the database structure every time the
application starts, it's use is no longer recommended. While it can
make for "flashy" demos, the use of the C<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).
=head2 Make Sure You Have a Recent Version of the DBIx::Class Model
First, let's be sure we have a recent version 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 DBIx::Class Schema Files
Use the model helper with the C<create=static> option to read the
database with
L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> and
automatically build the required files for us:
$ 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.
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 *
C<create=static> causes
L<DBIx::Class::Schema::Loader|DBIx::Class::Schema::Loader> to
load the schema as it runs and then write that information out
into files.
=item *
C<components=TimeStamp> causes the help to include the
L<DBIx::Class::TimeStamp|DBIx::Class::TimeStamp> DBIC component.
=item *
And finally, C<dbi:SQLite:myapp.db> is the standard DBI connect string
for use with SQLite.
=back
If you look in the C<lib/MyApp/Schema.pm> file, you will find that it
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 DBIx::Class 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 DBIx::Class 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).
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
=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 is
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 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
[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
DBIx::Class 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.
=head2 Updating the Generated DBIx::Class 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), DBIx::Class 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<$book-E<gt>book_authors-E<gt>first-E<gt>author-E<gt>last_name> (we
will see examples on how to use DBIx::Class objects in your code soon,
but note that because C<$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 an 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 development 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> and replace
the "empty" tabase cell with the following:
...
<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
DBIx::Class):
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 <
and > 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 perform 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 extend 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/>).