Catalyst::Manual::TutoUserCatalyst::Manual::Tutorial::03_MoreCatalystBasics(3)NAMECatalyst::Manual::Tutorial::03_MoreCatalystBasics - Catalyst Tutorial -
Chapter 3: More Catalyst Application Development Basics
OVERVIEW
This is Chapter 3 of 10 for the Catalyst tutorial.
Tutorial Overview
1. Introduction
2. Catalyst Basics
3. 03_More Catalyst Basics
4. Basic CRUD
5. Authentication
6. Authorization
7. Debugging
8. Testing
9. Advanced CRUD
10. Appendices
DESCRIPTION
This chapter of the tutorial builds on the work done in Chapter 2 to
explore some features that are more typical of "real world" web
applications. From this chapter of the tutorial onward, we will be
building a simple book database application. Although the application
will be too limited to be of use to anyone, it should provide a basic
environment where we can explore a variety of features used in
virtually all web applications.
Source code for the tutorial in included in the /home/catalyst/Final
directory of the Tutorial Virtual machine (one subdirectory per
chapter). There are also instructions for downloading the code in
Catalyst::Manual::Tutorial::01_Intro.
Please take a look at "STARTING WITH THE TUTORIAL VIRTUAL MACHINE" in
Catalyst::Manual::Tutorial::01_Intro before doing the rest of this
tutorial. Although the tutorial should work correctly under most any
recent version of Perl running on any operating system, the tutorial
has been written using the virtual machine that is available for
download. The entire tutorial has been tested to be sure it runs
correctly in this environment, so it is the most trouble-free way to
get started with Catalyst.
CREATE A NEW APPLICATION
The remainder of the tutorial will build an application called "MyApp".
First use the Catalyst "catalyst.pl" script to initialize the framework
for the "MyApp" application (make sure you aren't still inside the
directory of the "Hello" application from the previous chapter of the
tutorial or in a directory that already has a "MyApp" subdirectory):
$ catalyst.pl MyApp
created "MyApp"
created "MyApp/script"
created "MyApp/lib"
created "MyApp/root"
...
created "MyApp/script/myapp_create.pl"
Change to application directory and Run "perl Makefile.PL" to make sure your install is complete
And change the "MyApp" directory the helper created:
$ cd MyApp
This creates a similar skeletal structure to what we saw in Chapter 2
of the tutorial, except with "MyApp" and "myapp" substituted for
"Hello" and "hello". (As noted in Chapter 2, omit the ".pl" from the
command if you are using Strawberry Perl.)
EDIT THE LIST OF CATALYST PLUGINS
One of the greatest benefits of Catalyst is that it has such a large
library of bases classes and plugins available that you can use easily
add functionality to your application. Plugins are used to seamlessly
integrate existing Perl modules into the overall Catalyst framework. In
general, they do this by adding additional methods to the "context"
object (generally written as $c) that Catalyst passes to every
component throughout the framework.
Take a look at the file "lib/MyApp.pm" that the helper created above.
By default, Catalyst enables three plugins/flags:
· "-Debug" Flag
Enables the Catalyst debug output you saw when we started the
"script/myapp_server.pl" development server earlier. You can
remove this item when you place your application into production.
To be technically correct, it turns out that "-Debug" is not a
plugin, but a flag. Although most of the items specified on the
"use Catalyst" line of your application class will be plugins,
Catalyst supports a limited number of flag options (of these,
"-Debug" is the most common). See the documentation for
"https://metacpan.org/module/Catalyst|Catalyst.pm" to get details
on other flags (currently "-Engine", "-Home", "-Log", and
"-Stats").
If you prefer, there are several other ways to enable debug output:
· Use the "$c->debug" method on the $c Catalyst context object
· The "-d" option to "script/myapp_server.pl"
· The "CATALYST_DEBUG=1" environment variable (or use
"CATALYST_DEBUG=0" to temporarily disable debug output).
TIP: Depending on your needs, it can be helpful to permanently
remove "-Debug" from "lib/MyApp.pm" and then use the "-d" option to
"script/myapp_server.pl" to re-enable it when needed. We will not
be using that approach in the tutorial, but feel free to make use
of it in your own projects.
· Catalyst::Plugin::ConfigLoader
"ConfigLoader" provides an automatic way to load configurable
parameters for your application from a central Config::General file
(versus having the values hard-coded inside your Perl modules).
Config::General uses syntax very similar to Apache configuration
files. We will see how to use this feature of Catalyst during the
authentication and authorization sections (Chapter 5 and Chapter
6).
IMPORTANT NOTE: If you are using a version of Catalyst::Devel prior
to version 1.06, be aware that Catalyst changed the default format
from YAML to the more straightforward "Config::General" style.
This tutorial uses the newer "myapp.conf" file for
"Config::General". However, Catalyst supports both formats and will
automatically use either "myapp.conf" or "myapp.yml" (or any other
format supported by Catalyst::Plugin::ConfigLoader and
Config::Any). If you are using a version of Catalyst::Devel prior
to 1.06, you can convert to the newer format by simply creating the
"myapp.conf" file manually and deleting "myapp.yml". The default
contents of the "myapp.conf" you create should only consist of one
line:
name MyApp
TIP: This script can be useful for converting between configuration
formats:
perl -Ilib -e 'use MyApp; use Config::General;
Config::General->new->save_file("myapp.conf", MyApp->config);'
· Catalyst::Plugin::Static::Simple
"Static::Simple" provides an easy way to serve static content, such
as images and CSS files, from the development server.
For our application, we want to add one new plugin into the mix. To do
this, edit "lib/MyApp.pm" (this file is generally referred to as your
application class) and delete the lines with:
use Catalyst qw/
-Debug
ConfigLoader
Static::Simple
/;
Then replace it with:
# Load plugins
use Catalyst qw/
-Debug
ConfigLoader
Static::Simple
StackTrace
/;
Note: Recent versions of "Catalyst::Devel" have used a variety of
techniques to load these plugins/flags. For example, you might see the
following:
__PACKAGE__->setup(qw/-Debug ConfigLoader Static::Simple/);
Don't let these variations confuse you -- they all accomplish the same
result.
This tells Catalyst to start using one additional plugin,
Catalyst::Plugin::StackTrace, to add a stack trace near the top of the
standard Catalyst "debug screen" (the screen Catalyst sends to your
browser when an error occurs). Be aware that StackTrace output appears
in your browser, not in the console window from which you're running
your application, which is where logging output usually goes.
Make sure when adding new plugins you also include them as a new
dependency within the Makefile.PL file. For example, after adding the
StackTrace plugin the Makefile.PL should include the following line:
requires 'Catalyst::Plugin::StackTrace';
Notes:
· "__PACKAGE__" is just a shorthand way of referencing the name of
the package where it is used. Therefore, in "MyApp.pm",
"__PACKAGE__" is equivalent to "MyApp".
· You will want to disable StackTrace before you put your application
into production, but it can be helpful during development.
· When specifying plugins, you can omit "Catalyst::Plugin::" from the
name. Additionally, you can spread the plugin names across
multiple lines as shown here or place them all on one line.
· If you want to see what the StackTrace error screen looks like,
edit "lib/MyApp/Controller/Root.pm" and put a "die "Oops";" command
in the "sub index :Path :Args(0)" method. Then start the
development server and open "http://localhost:3000/" in your
browser. You should get a screen that starts with "Caught
exception in MyApp::Controller::Root->index" with sections showing
a stacktrace, information about the Request and Response objects,
the stash (something we will learn about soon), the applications
configuration configuration. Just don't forget to remove the die
before you continue the tutorial! :-)
CREATE A CATALYST CONTROLLER
As discussed earlier, controllers are where you write methods that
interact with user input. Typically, controller methods respond to
"GET" and "POST" requests from the user's web browser.
Use the Catalyst "create" script to add a controller for book-related
actions:
$ script/myapp_create.pl controller Books
exists "/home/catalyst/MyApp/script/../lib/MyApp/Controller"
exists "/home/catalyst/MyApp/script/../t"
created "/home/catalyst/MyApp/script/../lib/MyApp/Controller/Books.pm"
created "/home/catalyst/MyApp/script/../t/controller_Books.t"
Then edit "lib/MyApp/Controller/Books.pm" (as discussed in Chapter 2 of
the Tutorial, Catalyst has a separate directory under "lib/MyApp" for
each of the three parts of MVC: "Model", "View", and "Controller") and
add the following method to the controller:
=head2 list
Fetch all book objects and pass to books/list.tt2 in stash to be displayed
=cut
sub list :Local {
# Retrieve the usual Perl OO '$self' for this object. $c is the Catalyst
# 'Context' that's used to 'glue together' the various components
# that make up the application
my ($self, $c) = @_;
# Retrieve all of the book records as book model objects and store in the
# stash where they can be accessed by the TT template
# $c->stash(books => [$c->model('DB::Book')->all]);
# But, for now, use this code until we create the model later
$c->stash(books => '');
# Set the TT template to use. You will almost always want to do this
# in your action methods (action methods respond to user input in
# your controllers).
$c->stash(template => 'books/list.tt2');
}
TIP: See Appendix 1 for tips on removing the leading spaces when
cutting and pasting example code from POD-based documents.
Programmers experienced with object-oriented Perl should recognize
$self as a reference to the object where this method was called. On
the other hand, $c will be new to many Perl programmers who have not
used Catalyst before. This is the "Catalyst Context object", and it is
automatically passed as the second argument to all Catalyst action
methods. It is used to pass information between components and provide
access to Catalyst and plugin functionality.
Catalyst Controller actions are regular Perl methods, but they make use
of attributes (the "":Local"" next to the ""sub list"" in the code
above) to provide additional information to the Catalyst dispatcher
logic (note that there can be an optional space between the colon and
the attribute name; you will see attributes written both ways). Most
Catalyst Controllers use one of five action types:
· :Private -- Use ":Private" for methods that you want to make into
an action, but you do not want Catalyst to directly expose the
method to your users. Catalyst will not map ":Private" methods to
a URI. Use them for various sorts of "special" methods (the
"begin", "auto", etc. discussed below) or for methods you want to
be able to "forward" or "detach" to. (If the method is a "plain
old method" that you don't want to be an action at all, then just
define the method without any attribute -- you can call it in your
code, but the Catalyst dispatcher will ignore it. You will also
have to manually include $c if you want access to the context
object in the method vs. having Catalyst automatically include $c
in the argument list for you if it's a full-fledged action.)
There are five types of "special" built-in ":Private" actions:
"begin", "end", "default", "index", and "auto".
· With "begin", "end", "default", "index" private actions, only
the most specific action of each type will be called. For
example, if you define a "begin" action in your controller it
will override a "begin" action in your application/root
controller -- only the action in your controller will be
called.
· Unlike the other actions where only a single method is called
for each request, every auto action along the chain of
namespaces will be called. Each "auto" action will be called
from the application/root controller down through the most
specific class.
· :Path -- ":Path" actions let you map a method to an explicit URI
path. For example, "":Path('list')"" in
"lib/MyApp/Controller/Books.pm" would match on the URL
"http://localhost:3000/books/list", but "":Path('/list')"" would
match on "http://localhost:3000/list" (because of the leading
slash). You can use ":Args()" to specify how many arguments an
action should accept. See "Action_types" in
Catalyst::Manual::Intro for more information and examples.
· :Local -- ":Local" is merely a shorthand for
"":Path('_name_of_method_')"". For example, these are equivalent:
""sub create_book :Local {...}"" and ""sub create_book
:Path('create_book') {...}"".
· :Global -- ":Global" is merely a shorthand for
"":Path('/_name_of_method_')"". For example, these are equivalent:
""sub create_book :Global {...}"" and ""sub create_book
:Path('/create_book') {...}"".
· :Chained -- Newer Catalyst applications tend to use the Chained
dispatch form of action types because of its power and flexibility.
It allows a series of controller methods to be automatically
dispatched when servicing a single user request. See
Catalyst::Manual::Tutorial::04_BasicCRUD and
Catalyst::DispatchType::Chained for more information on chained
actions.
You should refer to "Action-types" in Catalyst::Manual::Intro for
additional information and for coverage of some lesser-used action
types not discussed here ("Regex" and "LocalRegex").
CATALYST VIEWS
As mentioned in Chapter 2 of the tutorial, views are where you render
output, typically for display in the user's web browser (but can
generate other types of output such as PDF or JSON). The code in
"lib/MyApp/View" selects the type of view to use, with the actual
rendering template found in the "root" directory. As with virtually
every aspect of Catalyst, options abound when it comes to the specific
view technology you adopt inside your application. However, most
Catalyst applications use the Template Toolkit, known as TT (for more
information on TT, see http://www.template-toolkit.org
<http://www.template-toolkit.org>). Other somewhat popular view
technologies include Mason (<http://www.masonhq.com> and
<http://www.masonbook.com>) and HTML::Template
(http://html-template.sourceforge.net <http://html-
template.sourceforge.net>).
Create a Catalyst View
When using TT for the Catalyst view, the main helper script is
Catalyst::Helper::View::TT. You may also come across references to
Catalyst::Helper::View::TTSite, but its use is now deprecated.
For our book application, enter the following command to enable the
"TT" style of view rendering:
$ script/myapp_create.pl view HTML TT
exists "/home/catalyst/MyApp/script/../lib/MyApp/View"
exists "/home/catalyst/MyApp/script/../t"
created "/home/catalyst/MyApp/script/../lib/MyApp/View/HTML.pm"
created "/home/catalyst/MyApp/script/../t/view_HTML.t"
This creates a view called "HTML" (the first argument) in a file called
"HTML.pm" that uses Catalyst::View::TT (the second argument) as the
"rendering engine".
It is now up to you to decide how you want to structure your view
layout. For the tutorial, we will start with a very simple TT template
to initially demonstrate the concepts, but quickly migrate to a more
typical "wrapper page" type of configuration (where the "wrapper"
controls the overall "look and feel" of your site from a single file or
set of files).
Edit "lib/MyApp/View/HTML.pm" and you should see something similar to
the following:
__PACKAGE__->config(
TEMPLATE_EXTENSION => '.tt',
render_die => 1,
);
And update it to match:
__PACKAGE__->config(
# Change default TT extension
TEMPLATE_EXTENSION => '.tt2',
render_die => 1,
);
This changes the default extension for Template Toolkit from '.tt' to
'.tt2'.
You can also configure components in your application class. For
example, Edit "lib/MyApp.pm" and you should see the default
configuration above the call to "_PACKAGE__->setup" (your defaults
could be different depending on the version of Catalyst you are using):
__PACKAGE__->config(
name => 'MyApp',
# Disable deprecated behavior needed by old applications
disable_component_resolution_regex_fallback => 1,
);
Change this to match the following (insert a new "__PACKAGE__->config"
below the existing statement):
__PACKAGE__->config(
name => 'MyApp',
# Disable deprecated behavior needed by old applications
disable_component_resolution_regex_fallback => 1,
);
__PACKAGE__->config(
# Configure the view
'View::HTML' => {
#Set the location for TT files
INCLUDE_PATH => [
__PACKAGE__->path_to( 'root', 'src' ),
],
},
);
This changes the base directory for your template files from "root" to
"root/src".
Please stick with the settings above for the duration of the tutorial,
but feel free to use whatever options you desire in your applications
(as with most things Perl, there's more than one way to do it...).
Note: We will use "root/src" as the base directory for our template
files, with a full naming convention of
"root/src/_controller_name_/_action_name_.tt2". Another popular option
is to use "root/" as the base (with a full filename pattern of
"root/_controller_name_/_action_name_.tt2").
Create a TT Template Page
First create a directory for book-related TT templates:
$ mkdir -p root/src/books
Then create "root/src/books/list.tt2" in your editor and enter:
[% # This is a TT comment. -%]
[%- # Provide a title -%]
[% META title = 'Book List' -%]
[% # Note That the '-' at the beginning or end of TT code -%]
[% # "chomps" the whitespace/newline at that end of the -%]
[% # output (use View Source in browser to see the effect) -%]
[% # Some basic HTML with a loop to display books -%]
<table>
<tr><th>Title</th><th>Rating</th><th>Author(s)</th></tr>
[% # Display each book in a table row %]
[% FOREACH book IN books -%]
<tr>
<td>[% book.title %]</td>
<td>[% book.rating %]</td>
<td></td>
</tr>
[% END -%]
</table>
As indicated by the inline comments above, the "META title" line uses
TT's META feature to provide a title to the "wrapper" that we will
create later (and essentially does nothing at the moment). Meanwhile,
the "FOREACH" loop iterates through each "book" model object and prints
the "title" and "rating" fields.
The "[%" and "%]" tags are used to delimit Template Toolkit code. TT
supports a wide variety of directives for "calling" other files,
looping, conditional logic, etc. In general, TT simplifies the usual
range of Perl operators down to the single dot (".") operator. This
applies to operations as diverse as method calls, hash lookups, and
list index values (see Template::Manual::Variables for details and
examples). In addition to the usual Template::Toolkit module Pod
documentation, you can access the TT manual at
<https://metacpan.org/module/Template::Manual>.
TIP: While you can build all sorts of complex logic into your TT
templates, you should in general keep the "code" part of your templates
as simple as possible. If you need more complex logic, create helper
methods in your model that abstract out a set of code into a single
call from your TT template. (Note that the same is true of your
controller logic as well -- complex sections of code in your
controllers should often be pulled out and placed into your model
objects.) In Chapter 4 of the tutorial we will explore some extremely
helpful and powerful features of DBIx::Class that allow you to pull
code out of your views and controllers and place it where it rightfully
belongs in a model class.
Test Run The Application
To test your work so far, first start the development server:
$ script/myapp_server.pl -r
Then point your browser to <http://localhost:3000> and you should still
get the Catalyst welcome page. Next, change the URL in your browser to
<http://localhost:3000/books/list>. If you have everything working so
far, you should see a web page that displays nothing other than our
column headers for "Title", "Rating", and "Author(s)" -- we will not
see any books until we get the database and model working below.
If you run into problems getting your application to run correctly, it
might be helpful to refer to some of the debugging techniques covered
in the Debugging chapter of the tutorial.
CREATE A SQLITE DATABASE
In this step, we make a text file with the required SQL commands to
create a database table and load some sample data. We will use SQLite
(<http://www.sqlite.org>), a popular database that is lightweight and
easy to use. Be sure to get at least version 3. Open "myapp01.sql" in
your editor and enter:
--
-- Create a very simple database to hold book and author information
--
PRAGMA foreign_keys = ON;
CREATE TABLE book (
id INTEGER PRIMARY KEY,
title TEXT ,
rating INTEGER
);
-- 'book_author' is a many-to-many join table between books & authors
CREATE TABLE book_author (
book_id INTEGER REFERENCES book(id) ON DELETE CASCADE ON UPDATE CASCADE,
author_id INTEGER REFERENCES author(id) ON DELETE CASCADE ON UPDATE CASCADE,
PRIMARY KEY (book_id, author_id)
);
CREATE TABLE author (
id INTEGER PRIMARY KEY,
first_name TEXT,
last_name TEXT
);
---
--- Load some sample data
---
INSERT INTO book VALUES (1, 'CCSP SNRS Exam Certification Guide', 5);
INSERT INTO book VALUES (2, 'TCP/IP Illustrated, Volume 1', 5);
INSERT INTO book VALUES (3, 'Internetworking with TCP/IP Vol.1', 4);
INSERT INTO book VALUES (4, 'Perl Cookbook', 5);
INSERT INTO book VALUES (5, 'Designing with Web Standards', 5);
INSERT INTO author VALUES (1, 'Greg', 'Bastien');
INSERT INTO author VALUES (2, 'Sara', 'Nasseh');
INSERT INTO author VALUES (3, 'Christian', 'Degu');
INSERT INTO author VALUES (4, 'Richard', 'Stevens');
INSERT INTO author VALUES (5, 'Douglas', 'Comer');
INSERT INTO author VALUES (6, 'Tom', 'Christiansen');
INSERT INTO author VALUES (7, 'Nathan', 'Torkington');
INSERT INTO author VALUES (8, 'Jeffrey', 'Zeldman');
INSERT INTO book_author VALUES (1, 1);
INSERT INTO book_author VALUES (1, 2);
INSERT INTO book_author VALUES (1, 3);
INSERT INTO book_author VALUES (2, 4);
INSERT INTO book_author VALUES (3, 5);
INSERT INTO book_author VALUES (4, 6);
INSERT INTO book_author VALUES (4, 7);
INSERT INTO book_author VALUES (5, 8);
Then use the following command to build a "myapp.db" SQLite database:
$ sqlite3 myapp.db < myapp01.sql
If you need to create the database more than once, you probably want to
issue the "rm myapp.db" command to delete the database before you use
the "sqlite3 myapp.db < myapp01.sql" command.
Once the "myapp.db" database file has been created and initialized, you
can use the SQLite command line environment to do a quick dump of the
database contents:
$ sqlite3 myapp.db
SQLite version 3.7.3
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite> select * from book;
1|CCSP SNRS Exam Certification Guide|5
2|TCP/IP Illustrated, Volume 1|5
3|Internetworking with TCP/IP Vol.1|4
4|Perl Cookbook|5
5|Designing with Web Standards|5
sqlite> .q
$
Or:
$ sqlite3 myapp.db "select * from book"
1|CCSP SNRS Exam Certification Guide|5
2|TCP/IP Illustrated, Volume 1|5
3|Internetworking with TCP/IP Vol.1|4
4|Perl Cookbook|5
5|Designing with Web Standards|5
As with most other SQL tools, if you are using the full "interactive"
environment you need to terminate your SQL commands with a ";" (it's
not required if you do a single SQL statement on the command line).
Use ".q" to exit from SQLite from the SQLite interactive mode and
return to your OS command prompt.
Please note that here we have chosen to use 'singular' table names.
This is because the default inflection code for older versions of
DBIx::Class::Schema::Loader does NOT handle plurals. There has been
much philosophical discussion on whether table names should be plural
or singular. There is no one correct answer, as long as one makes a
choice and remains consistent with it. If you prefer plural table names
(e.g. you think that they are easier to read) then see the
documentation in "naming" in DBIx::Class::Schema::Loader::Base (version
0.05 or greater).
For using other databases, such as PostgreSQL or MySQL, see Appendix 2.
DATABASE ACCESS WITH DBIx::Class
Catalyst can be used with virtually any form of datastore available via
Perl. For example, Catalyst::Model::DBI can be used to access
databases through the traditional Perl DBI interface or you can use a
model to access files of any type on the filesystem. However, most
Catalyst applications use some form of object-relational mapping (ORM)
technology to create objects associated with tables in a relational
database, and Matt Trout's DBIx::Class (abbreviated as "DBIC") is the
usual choice (this tutorial will use DBIx::Class).
Although DBIx::Class has included support for a "create=dynamic" mode
to automatically read the database structure every time the application
starts, its use is no longer recommended. While it can make for
"flashy" demos, the use of the "create=static" mode we use below can be
implemented just as quickly and provides many advantages (such as the
ability to add your own methods to the overall DBIC framework, a
technique that we see in Chapter 4).
Create Static DBIx::Class Schema Files
Note: If you are not following along in the Tutorial Virtual Machine,
please be sure that you have version 1.27 or higher of DBD::SQLite and
version 0.39 or higher of Catalyst::Model::DBIC::Schema. (The Tutorial
VM already has versions that are known to work.) You can get your
currently installed version numbers with the following commands.
$ perl -MCatalyst::Model::DBIC::Schema\ 999
$ perl -MDBD::SQLite\ 999
Before you continue, make sure your "myapp.db" database file is in the
application's topmost directory. Now use the model helper with the
"create=static" option to read the database with
DBIx::Class::Schema::Loader and automatically build the required files
for us:
$ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema \
create=static dbi:SQLite:myapp.db \
on_connect_do="PRAGMA foreign_keys = ON"
exists "/home/catalyst/MyApp/script/../lib/MyApp/Model"
exists "/home/catalyst/MyApp/script/../t"
Dumping manual schema for MyApp::Schema to directory /home/catalyst/MyApp/script/../lib ...
Schema dump completed.
created "/home/catalyst/MyApp/script/../lib/MyApp/Model/DB.pm"
created "/home/catalyst/MyApp/script/../t/model_DB.t"
Please note the '\' above. Depending on your environment, you might be
able to cut and paste the text as shown or need to remove the '\'
character to that the command is all on a single line.
The "script/myapp_create.pl" command breaks down like this:
· "DB" is the name of the model class to be created by the helper in
the "lib/MyApp/Model" directory.
· "DBIC::Schema" is the type of the model to create. This equates to
Catalyst::Model::DBIC::Schema, the standard way to use a DBIC-based
model inside of Catalyst.
· "MyApp::Schema" is the name of the DBIC schema file written to
"lib/MyApp/Schema.pm".
· "create=static" causes DBIx::Class::Schema::Loader to load the
schema as it runs and then write that information out into
"lib/MyApp/Schema.pm" and files under the "lib/MyApp/Schema"
directory.
· "dbi:SQLite:myapp.db" is the standard DBI connect string for use
with SQLite.
· And finally, the "on_connect_do" string requests that
DBIx::Class::Schema::Loader create foreign key relationships for us
(this is not needed for databases such as PostgreSQL and MySQL, but
is required for SQLite). If you take a look at
"lib/MyApp/Model/DB.pm", you will see that the SQLite pragma is
propagated to the Model, so that SQLite's recent (and optional)
foreign key enforcement is enabled at the start of every database
connection.
If you look in the "lib/MyApp/Schema.pm" file, you will find that it
only contains a call to the "load_namespaces" method. You will also
find that "lib/MyApp" contains a "Schema" subdirectory, which then has
a subdirectory called "Result". This "Result" subdirectory then has
files named according to each of the tables in our simple database
("Author.pm", "BookAuthor.pm", and "Book.pm"). These three files are
called "Result Classes" (or "ResultSource Classes") in DBIx::Class
nomenclature. Although the Result Class files are named after tables in
our database, the classes correspond to the row-level data that is
returned by DBIC (more on this later, especially in "EXPLORING THE
POWER OF DBIC" in Catalyst::Manual::Tutorial::04_BasicCRUD).
The idea with the Result Source files created under
"lib/MyApp/Schema/Result" by the "create=static" option is to only edit
the files below the "# DO NOT MODIFY THIS OR ANYTHING ABOVE!" warning.
If you place all of your changes below that point in the file, you can
regenerate the automatically created information at the top of each
file should your database structure get updated.
Also note the "flow" of the model information across the various files
and directories. Catalyst will initially load the model from
"lib/MyApp/Model/DB.pm". This file contains a reference to
"lib/MyApp/Schema.pm", so that file is loaded next. Finally, the call
to "load_namespaces" in "Schema.pm" will load each of the "Result
Class" files from the "lib/MyApp/Schema/Result" subdirectory. The
final outcome is that Catalyst will dynamically create three table-
specific Catalyst models every time the application starts (you can see
these three model files listed in the debug output generated when you
launch the application).
Additionally, the "lib/MyApp/Schema.pm" model can easily be loaded
outside of Catalyst, for example, in command-line utilities and/or cron
jobs. "lib/MyApp/Model/DB.pm" provides a very thin "bridge" between
Catalyst this external database model. Once you see how we can add
some powerful features to our DBIC model in Chapter 4, the elegance of
this approach will start to become more obvious.
NOTE: Older versions of Catalyst::Model::DBIC::Schema use the
deprecated DBIx::Class "load_classes" technique instead of the newer
"load_namespaces". For new applications, please try to use
"load_namespaces" since it more easily supports a very useful DBIC
technique called "ResultSet Classes." If you need to convert an
existing application from "load_classes" to "load_namespaces," you can
use this process to automate the migration, but first make sure you
have version 0.39 of Catalyst::Model::DBIC::Schema and
DBIx::Class::Schema::Loader version 0.05000 or later.
$ # Re-run the helper to upgrade for you
$ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema \
create=static naming=current use_namespaces=1 \
dbi:SQLite:myapp.db \
on_connect_do="PRAGMA foreign_keys = ON"
ENABLE THE MODEL IN THE CONTROLLER
Open "lib/MyApp/Controller/Books.pm" and un-comment the model code we
left disabled earlier so that your version matches the following (un-
comment the line containing "[$c->model('DB::Book')->all]" and delete
the next 2 lines):
=head2 list
Fetch all book objects and pass to books/list.tt2 in stash to be displayed
=cut
sub list :Local {
# Retrieve the usual Perl OO '$self' for this object. $c is the Catalyst
# 'Context' that's used to 'glue together' the various components
# that make up the application
my ($self, $c) = @_;
# Retrieve all of the book records as book model objects and store
# in the stash where they can be accessed by the TT template
$c->stash(books => [$c->model('DB::Book')->all]);
# Set the TT template to use. You will almost always want to do this
# in your action methods (action methods respond to user input in
# your controllers).
$c->stash(template => 'books/list.tt2');
}
TIP: You may see the "$c->model('DB::Book')" un-commented above written
as "$c->model('DB')->resultset('Book')". The two are equivalent.
Either way, "$c->model" returns a DBIx::Class::ResultSet which handles
queries against the database and iterating over the set of results that
is returned.
We are using the "->all" to fetch all of the books. DBIC supports a
wide variety of more advanced operations to easily do things like
filtering and sorting the results. For example, the following could be
used to sort the results by descending title:
$c->model('DB::Book')->search({}, {order_by => 'title DESC'});
Some other examples are provided in "Complex WHERE clauses" in
DBIx::Class::Manual::Cookbook, with additional information found at
"search" in DBIx::Class::ResultSet, "Searching" in
DBIx::Class::Manual::FAQ, DBIx::Class::Manual::Intro and
Catalyst::Model::DBIC::Schema.
Test Run The Application
First, let's enable an environment variable that causes DBIx::Class to
dump the SQL statements used to access the database. This is a helpful
trick when you are trying to debug your database-oriented code. Press
"Ctrl-C" to break out of the development server and enter:
$ export DBIC_TRACE=1
$ script/myapp_server.pl -r
This assumes you are using bash as your shell -- adjust accordingly if
you are using a different shell (for example, under tcsh, use "setenv
DBIC_TRACE 1").
NOTE: You can also set this in your code using
"$class->storage->debug(1);". See DBIx::Class::Manual::Troubleshooting
for details (including options to log to a file instead of displaying
to the Catalyst development server log).
Then launch the Catalyst development server. The log output should
display something like:
$ script/myapp_server.pl -r
[debug] Debug messages enabled
[debug] Statistics enabled
[debug] Loaded plugins:
.----------------------------------------------------------------------------.
| Catalyst::Plugin::ConfigLoader 0.30 |
| Catalyst::Plugin::StackTrace 0.11 |
'----------------------------------------------------------------------------'
[debug] Loaded dispatcher "Catalyst::Dispatcher"
[debug] Loaded engine "Catalyst::Engine"
[debug] Found home "/home/catalyst/MyApp"
[debug] Loaded Config "/home/catalyst/MyApp/myapp.conf"
[debug] Loaded components:
.-----------------------------------------------------------------+----------.
| Class | Type |
+-----------------------------------------------------------------+----------+
| MyApp::Controller::Books | instance |
| MyApp::Controller::Root | instance |
| MyApp::Model::DB | instance |
| MyApp::Model::DB::Author | class |
| MyApp::Model::DB::Book | class |
| MyApp::Model::DB::BookAuthor | class |
| MyApp::View::HTML | instance |
'-----------------------------------------------------------------+----------'
[debug] Loaded Private actions:
.----------------------+--------------------------------------+--------------.
| Private | Class | Method |
+----------------------+--------------------------------------+--------------+
| /default | MyApp::Controller::Root | default |
| /end | MyApp::Controller::Root | end |
| /index | MyApp::Controller::Root | index |
| /books/index | MyApp::Controller::Books | index |
| /books/list | MyApp::Controller::Books | list |
'----------------------+--------------------------------------+--------------'
[debug] Loaded Path actions:
.-------------------------------------+--------------------------------------.
| Path | Private |
+-------------------------------------+--------------------------------------+
| / | /default |
| / | /index |
| /books | /books/index |
| /books/list | /books/list |
'-------------------------------------+--------------------------------------'
[info] MyApp powered by Catalyst 5.80020
HTTP::Server::PSGI: Accepting connections at http://0:3000
NOTE: Be sure you run the "script/myapp_server.pl" command from the
'base' directory of your application, not inside the "script" directory
itself or it will not be able to locate the "myapp.db" database file.
You can use a fully qualified or a relative path to locate the database
file, but we did not specify that when we ran the model helper earlier.
Some things you should note in the output above:
· Catalyst::Model::DBIC::Schema dynamically created three model
classes, one to represent each of the three tables in our database
("MyApp::Model::DB::Author", "MyApp::Model::DB::BookAuthor", and
"MyApp::Model::DB::Book").
· The "list" action in our Books controller showed up with a path of
"/books/list".
Point your browser to <http://localhost:3000> and you should still get
the Catalyst welcome page.
Next, to view the book list, change the URL in your browser to
<http://localhost:3000/books/list>. You should get a list of the five
books loaded by the "myapp01.sql" script above without any formatting.
The rating for each book should appear on each row, but the "Author(s)"
column will still be blank (we will fill that in later).
Also notice in the output of the "script/myapp_server.pl" that
DBIx::Class used the following SQL to retrieve the data:
SELECT me.id, me.title, me.rating FROM book me
because we enabled DBIC_TRACE.
You now have the beginnings of a simple but workable web application.
Continue on to future sections and we will develop the application more
fully.
CREATE A WRAPPER FOR THE VIEW
When using TT, you can (and should) create a wrapper that will
literally wrap content around each of your templates. This is
certainly useful as you have one main source for changing things that
will appear across your entire site/application instead of having to
edit many individual files.
Configure HTML.pm For The Wrapper
In order to create a wrapper, you must first edit your TT view and tell
it where to find your wrapper file.
Edit your TT view in "lib/MyApp/View/HTML.pm" and change it to match
the following:
__PACKAGE__->config(
# Change default TT extension
TEMPLATE_EXTENSION => '.tt2',
# Set the location for TT files
INCLUDE_PATH => [
MyApp->path_to( 'root', 'src' ),
],
# Set to 1 for detailed timer stats in your HTML as comments
TIMER => 0,
# This is your wrapper template located in the 'root/src'
WRAPPER => 'wrapper.tt2',
);
Create the Wrapper Template File and Stylesheet
Next you need to set up your wrapper template. Basically, you'll want
to take the overall layout of your site and put it into this file. For
the tutorial, open "root/src/wrapper.tt2" and input the following:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" [%#
%]"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>[% template.title or "My Catalyst App!" %]</title>
<link rel="stylesheet" href="[% c.uri_for('/static/css/main.css') %]" />
</head>
<body>
<div id="outer">
<div id="header">
[%# Your logo could go here -%]
<img src="[% c.uri_for('/static/images/btn_88x31_powered.png') %]" />
[%# Insert the page title -%]
<h1>[% template.title or site.title %]</h1>
</div>
<div id="bodyblock">
<div id="menu">
Navigation:
<ul>
<li><a href="[% c.uri_for('/books/list') %]">Home</a></li>
<li><a href="[% c.uri_for('/')
%]" title="Catalyst Welcome Page">Welcome</a></li>
</ul>
</div><!-- end menu -->
<div id="content">
[%# Status and error messages %]
<span class="message">[% status_msg %]</span>
<span class="error">[% error_msg %]</span>
[%# This is where TT will stick all of your template's contents. -%]
[% content %]
</div><!-- end content -->
</div><!-- end bodyblock -->
<div id="footer">Copyright (c) your name goes here</div>
</div><!-- end outer -->
</body>
</html>
Notice the status and error message sections in the code above:
<span class="status">[% status_msg %]</span>
<span class="error">[% error_msg %]</span>
If we set either message in the Catalyst stash (e.g.,
"$c->stash->{status_msg} = 'Request was successful!'") it will be
displayed whenever any view used by that request is rendered. The
"message" and "error" CSS styles can be customized to suit your needs
in the "root/static/css/main.css" file we create below.
Notes:
· The Catalyst stash only lasts for a single HTTP request. If you
need to retain information across requests you can use
Catalyst::Plugin::Session (we will use Catalyst sessions in the
Authentication chapter of the tutorial).
· Although it is beyond the scope of this tutorial, you may wish to
use a JavaScript or AJAX tool such as jQuery
(<http://www.jquery.com>) or Dojo (<http://www.dojotoolkit.org>).
Create A Basic Stylesheet
First create a central location for stylesheets under the static
directory:
$ mkdir root/static/css
Then open the file "root/static/css/main.css" (the file referenced in
the stylesheet href link of our wrapper above) and add the following
content:
#header {
text-align: center;
}
#header h1 {
margin: 0;
}
#header img {
float: right;
}
#footer {
text-align: center;
font-style: italic;
padding-top: 20px;
}
#menu {
font-weight: bold;
background-color: #ddd;
}
#menu ul {
list-style: none;
float: left;
margin: 0;
padding: 0 0 50% 5px;
font-weight: normal;
background-color: #ddd;
width: 100px;
}
#content {
margin-left: 120px;
}
.message {
color: #390;
}
.error {
color: #f00;
}
You may wish to check out a "CSS Framework" like Emastic
(<http://code.google.com/p/emastic/>) as a way to quickly provide lots
of high-quality CSS functionality.
Test Run The Application
Hit "Reload" in your web browser and you should now see a formatted
version of our basic book list. (Again, the development server should
have automatically restarted when you made changes to
"lib/MyApp/View/HTML.pm". If you are not using the "-r" option, you
will need to hit "Ctrl-C" and manually restart it. Also note that the
development server does NOT need to restart for changes to the TT and
static files we created and edited in the "root" directory -- those
updates are handled on a per-request basis.)
Although our wrapper and stylesheet are obviously very simple, you
should see how it allows us to control the overall look of an entire
website from two central files. To add new pages to the site, just
provide a template that fills in the "content" section of our wrapper
template -- the wrapper will provide the overall feel of the page.
Updating the Generated DBIx::Class Result Class Files
If you take a look at the Schema files automatically generated by
DBIx::Class::Schema::Loader, you will see that it has already defined
"has_many" and "belongs_to" relationships on each side of our foreign
keys. For example, take a look at "lib/MyApp/Schema/Result/Book.pm" and
notice the following code:
=head1 RELATIONS
=head2 book_authors
Type: has_many
Related object: L<MyApp::Schema::Result::BookAuthor>
=cut
__PACKAGE__->has_many(
"book_authors",
"MyApp::Schema::Result::BookAuthor",
{ "foreign.book_id" => "self.id" },
{ cascade_copy => 0, cascade_delete => 0 },
);
Each "Book" "has_many" "book_authors", where "BookAuthor" is the many-
to-many table that allows each Book to have multiple Authors, and each
Author to have multiple books. The arguments to "has_many" are:
· "book_authors" - The name for this relationship. DBIC will create
an accessor on the "Books" DBIC Row object with this name.
· "MyApp::Schema::Result::BookAuthor" - The name of the DBIC model
class referenced by this "has_many" relationship.
· "foreign.book_id" - "book_id" is the name of the foreign key column
in the foreign table that points back to this table.
· "self.id" - "id" is the name of the column in this table that is
referenced by the foreign key.
See "has_many" in DBIx::Class::Relationship for additional information.
Note that you might see a "hand coded" version of the "has_many"
relationship above expressed as:
__PACKAGE__->has_many(
"book_authors",
"MyApp::Schema::Result::BookAuthor",
"book_id",
);
Where the third argument is simply the name of the column in the
foreign table. However, the hashref syntax used by
DBIx::Class::Schema::Loader is more flexible (for example, it can
handle "multi-column foreign keys").
Note: If you are using older versions of SQLite and related DBIC tools,
you will need to manually define your "has_many" and "belongs_to"
relationships. We recommend upgrading to the versions specified above.
:-)
Have a look at "lib/MyApp/Schema/Result/BookAuthor.pm" and notice that
there is a "belongs_to" relationship defined that acts as the "mirror
image" to the "has_many" relationship we just looked at above:
=head1 RELATIONS
=head2 book
Type: belongs_to
Related object: L<MyApp::Schema::Result::Book>
=cut
__PACKAGE__->belongs_to(
"book",
"MyApp::Schema::Result::Book",
{ id => "book_id" },
{ join_type => "LEFT", on_delete => "CASCADE", on_update => "CASCADE" },
);
The arguments are similar, but see "belongs_to" in
DBIx::Class::Relationship for the details.
Although recent versions of SQLite and DBIx::Class::Schema::Loader
automatically handle the "has_many" and "belongs_to" relationships,
"many_to_many" relationship bridges (not technically a relationship)
currently need to be manually inserted. To add a "many_to_many"
relationship bridge, first edit "lib/MyApp/Schema/Result/Book.pm" and
add the following text below the "# You can replace this text..."
comment:
# many_to_many():
# args:
# 1) Name of relationship bridge, DBIC will create accessor with this name
# 2) Name of has_many() relationship this many_to_many() is shortcut for
# 3) Name of belongs_to() relationship in model class of has_many() above
# You must already have the has_many() defined to use a many_to_many().
__PACKAGE__->many_to_many(authors => 'book_authors', 'author');
Note: Be careful to put this code above the "1;" at the end of the
file. As with any Perl package, we need to end the last line with a
statement that evaluates to "true". This is customarily done with "1;"
on a line by itself.
The "many_to_many" relationship bridge is optional, but it makes it
easier to map a book to its collection of authors. Without it, we
would have to "walk" through the "book_author" table as in
"$book->book_author->first->author->last_name" (we will see examples on
how to use DBIx::Class objects in your code soon, but note that because
"$book->book_author" can return multiple authors, we have to use
"first" to display a single author). "many_to_many" allows us to use
the shorter "$book->author->first->last_name". Note that you cannot
define a "many_to_many" relationship bridge without also having the
"has_many" relationship in place.
Then edit "lib/MyApp/Schema/Result/Author.pm" and add the reverse
"many_to_many" relationship bridge for "Author" as follows (again, be
careful to put in above the "1;" but below the "# DO NOT MODIFY THIS OR
ANYTHING ABOVE!" comment):
# many_to_many():
# args:
# 1) Name of relationship bridge, DBIC will create accessor with this name
# 2) Name of has_many() relationship this many_to_many() is shortcut for
# 3) Name of belongs_to() relationship in model class of has_many() above
# You must already have the has_many() defined to use a many_to_many().
__PACKAGE__->many_to_many(books => 'book_authors', 'book');
Run The Application
Run the Catalyst development server script with the "DBIC_TRACE" option
(it might still be enabled from earlier in the tutorial, but here is an
alternate way to specify the trace option just in case):
$ DBIC_TRACE=1 script/myapp_server.pl -r
Make sure that the application loads correctly and that you see the
three dynamically created model class (one for each of the Result
Classes we created).
Then hit the URL <http://localhost:3000/books/list> with your browser
and be sure that the book list still displays correctly.
Note: You will not see the authors yet because the view isn't taking
advantage of these relationships. Read on to the next section where we
update the template to do that.
UPDATING THE VIEW
Let's add a new column to our book list page that takes advantage of
the relationship information we manually added to our schema files in
the previous section. Edit "root/src/books/list.tt2" and replace the
"empty" table cell "<td></td>" with the following:
...
<td>
[% # NOTE: See Chapter 4 for a better way to do this! -%]
[% # First initialize a TT variable to hold a list. Then use a TT FOREACH -%]
[% # loop in 'side effect notation' to load just the last names of the -%]
[% # authors into the list. Note that the 'push' TT vmethod doesn't return -%]
[% # a value, so nothing will be printed here. But, if you have something -%]
[% # in TT that does return a value and you don't want it printed, you -%]
[% # 1) assign it to a bogus value, or -%]
[% # 2) use the CALL keyword to call it and discard the return value. -%]
[% tt_authors = [ ];
tt_authors.push(author.last_name) FOREACH author = book.authors %]
[% # Now use a TT 'virtual method' to display the author count in parens -%]
[% # Note the use of the TT filter "| html" to escape dangerous characters -%]
([% tt_authors.size | html %])
[% # Use another TT vmethod to join & print the names & comma separators -%]
[% tt_authors.join(', ') | html %]
</td>
...
IMPORTANT NOTE: Again, you should keep as much "logic code" as possible
out of your views. This kind of logic belongs in your model (the same
goes for controllers -- keep them as "thin" as possible and push all of
the "complicated code" out to your model objects). Avoid code like you
see in the previous example -- we are only using it here to show some
extra features in TT until we get to the more advanced model features
we will see in Chapter 4 (see "EXPLORING THE POWER OF DBIC" in
Catalyst::Manual::Tutorial::04_BasicCRUD).
Then hit "Reload" in your browser (note that you don't need to reload
the development server or use the "-r" option when updating TT
templates) and you should now see the number of authors each book has
along with a comma-separated list of the authors' last names. (If you
didn't leave the development server running from the previous step, you
will obviously need to start it before you can refresh your browser
window.)
If you are still running the development server with "DBIC_TRACE"
enabled, you should also now see five more "SELECT" statements in the
debug output (one for each book as the authors are being retrieved by
DBIx::Class):
SELECT me.id, me.title, me.rating FROM book me:
SELECT author.id, author.first_name, author.last_name FROM book_author me
JOIN author author ON author.id = me.author_id WHERE ( me.book_id = ? ): '1'
SELECT author.id, author.first_name, author.last_name FROM book_author me
JOIN author author ON author.id = me.author_id WHERE ( me.book_id = ? ): '2'
SELECT author.id, author.first_name, author.last_name FROM book_author me
JOIN author author ON author.id = me.author_id WHERE ( me.book_id = ? ): '3'
SELECT author.id, author.first_name, author.last_name FROM book_author me
JOIN author author ON author.id = me.author_id WHERE ( me.book_id = ? ): '4'
SELECT author.id, author.first_name, author.last_name FROM book_author me
JOIN author author ON author.id = me.author_id WHERE ( me.book_id = ? ): '5'
Also note in "root/src/books/list.tt2" that we are using "| html", a
type of TT filter, to escape characters such as < and > to < 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 Template::Filters. (While we are on
the topic of security and escaping of dangerous values, one of the
advantages of using tools like DBIC for database access or HTML::FormFu
for form management [see Chapter 9 is that they automatically handle
most escaping for you and therefore dramatically increase the security
of your app.)
RUNNING THE APPLICATION FROM THE COMMAND LINE
In some situations, it can be useful to run your application and
display a page without using a browser. Catalyst lets you do this
using the "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 "Ctrl+C" out of the development server and
then type:
$ script/myapp_test.pl "/books/list"
You should get the same text as if you visited
<http://localhost:3000/books/list> with the normal development server
and asked your browser to view the page source. You can even pipe this
HTML text output to a text-based browser using a command like:
$ script/myapp_test.pl "/books/list" | lynx -stdin
And you should see a fully rendered text-based view of your page. (If
you are following along in Debian 6, type "sudo aptitude -y install
lynx" to install lynx.) If you do start lynx, you can use the "Q" key
to quit.
OPTIONAL INFORMATION
NOTE: The rest of this chapter of the tutorial is optional. You can
skip to Chapter 4, Basic CRUD, if you wish.
Using 'RenderView' for the Default View
Once your controller logic has processed the request from a user, it
forwards processing to your view in order to generate the appropriate
response output. Catalyst uses Catalyst::Action::RenderView by default
to automatically perform this operation. If you look in
"lib/MyApp/Controller/Root.pm", you should see the empty definition for
the "sub end" method:
sub end : ActionClass('RenderView') {}
The following bullet points provide a quick overview of the
"RenderView" process:
· "Root.pm" is designed to hold application-wide logic.
· At the end of a given user request, Catalyst will call the most
specific "end" method that's appropriate. For example, if the
controller for a request has an "end" method defined, it will be
called. However, if the controller does not define a controller-
specific "end" method, the "global" "end" method in "Root.pm" will
be called.
· Because the definition includes an "ActionClass" attribute, the
Catalyst::Action::RenderView logic will be executed after any code
inside the definition of "sub end" is run. See
Catalyst::Manual::Actions for more information on "ActionClass".
· Because "sub end" is empty, this effectively just runs the default
logic in "RenderView". However, you can easily extend the
"RenderView" logic by adding your own code inside the empty method
body ("{}") created by the Catalyst Helpers when we first ran the
"catalyst.pl" to initialize our application. See
Catalyst::Action::RenderView for more detailed information on how
to extend "RenderView" in "sub end".
RenderView's "dump_info" Feature
One of the nice features of "RenderView" is that it automatically
allows you to add "dump_info=1" to the end of any URL for your
application and it will force the display of the "exception dump"
screen to the client browser. You can try this out by pointing your
browser to this URL:
http://localhost:3000/books/list?dump_info=1
You should get a page with the following message at the top:
Caught exception in MyApp::Controller::Root->end "Forced debug -
Scrubbed output at /usr/share/perl5/Catalyst/Action/RenderView.pm line 46."
Along with a summary of your application's state at the end of the
processing for that request. The "Stash" section should show a
summarized version of the DBIC book model objects. If desired, you can
adjust the summarization logic (called "scrubbing" logic) -- see
Catalyst::Action::RenderView for details.
Note that you shouldn't need to worry about "normal clients" using this
technique to "reverse engineer" your application -- "RenderView" only
supports the "dump_info=1" feature when your application is running in
"-Debug" mode (something you won't do once you have your application
deployed in production).
Using The Default Template Name
By default, "Catalyst::View::TT" will look for a template that uses the
same name as your controller action, allowing you to save the step of
manually specifying the template name in each action. For example,
this would allow us to remove the "$c->stash->{template} =
'books/list.tt2';" line of our "list" action in the Books controller.
Open "lib/MyApp/Controller/Books.pm" in your editor and comment out
this line to match the following (only the "$c->stash->{template}" line
has changed):
=head2 list
Fetch all book objects and pass to books/list.tt2 in stash to be displayed
=cut
sub list :Local {
# Retrieve the usual Perl OO '$self' for this object. $c is the Catalyst
# 'Context' that's used to 'glue together' the various components
# that make up the application
my ($self, $c) = @_;
# Retrieve all of the book records as book model objects and store in the
# stash where they can be accessed by the TT template
$c->stash(books => [$c->model('DB::Book')->all]);
# Set the TT template to use. You will almost always want to do this
# in your action methods (actions methods respond to user input in
# your controllers).
#$c->stash(template => 'books/list.tt2');
}
You should now be able to access the <http://localhost:3000/books/list>
URL as before.
NOTE: Please note that if you use the default template technique, you
will not be able to use either the "$c->forward" or the "$c->detach"
mechanisms (these are discussed in Chapter 2 and Chapter 9 of the
Tutorial).
IMPORTANT: Make sure that you do NOT skip the following section before
continuing to the next chapter 4 Basic CRUD.
Return To A Manually Specified Template
In order to be able to use "$c->forward" and "$c->detach" later in the
tutorial, you should remove the comment from the statement in "sub
list" in "lib/MyApp/Controller/Books.pm":
$c->stash(template => 'books/list.tt2');
Then delete the "TEMPLATE_EXTENSION" line in "lib/MyApp/View/HTML.pm".
Check the <http://localhost:3000/books/list> URL in your browser. It
should look the same manner as with earlier sections.
You can jump to the next chapter of the tutorial here: Basic CRUD
AUTHOR
Kennedy Clark, "hkclark@gmail.com"
Feel free to contact the author for any errors or suggestions, but the
best way to report issues is via the CPAN RT Bug system at
https://rt.cpan.org/Public/Dist/Display.html?Name=Catalyst-Manual
<https://rt.cpan.org/Public/Dist/Display.html?Name=Catalyst-Manual>.
Copyright 2006-2011, Kennedy Clark, under the Creative Commons
Attribution Share-Alike License Version 3.0
(http://creativecommons.org/licenses/by-sa/3.0/us/
<http://creativecommons.org/licenses/by-sa/3.0/us/>).
perl v5.14.2Catalyst::Manual::Tutorial::03_MoreCatalystBasics(3)