NAME¶
Catalyst::Manual::Tutorial::03_MoreCatalystBasics - Catalyst Tutorial - Chapter
3: More Catalyst Application Development Basics
OVERVIEW¶
This is
Chapter 3 of 10 for the Catalyst tutorial.
Tutorial Overview
- 1.
- Introduction
- 2.
- Catalyst Basics
- 3.
- 03_More Catalyst Basics
- 4.
- Basic CRUD
- 5.
- Authentication
- 6.
- Authorization
- 7.
- Debugging
- 8.
- Testing
- 9.
- Advanced CRUD
- 10.
- Appendices
DESCRIPTION¶
This chapter of the tutorial builds on the work done in Chapter 2 to explore
some features that are more typical of "real world" web
applications. From this chapter of the tutorial onward, we will be building a
simple book database application. Although the application will be too limited
to be of use to anyone, it should provide a basic environment where we can
explore a variety of features used in virtually all web applications.
Source code for the tutorial in included in the
/home/catalyst/Final
directory of the Tutorial Virtual machine (one subdirectory per chapter).
There are also instructions for downloading the code in
Catalyst::Manual::Tutorial::01_Intro.
Please take a look at "STARTING WITH THE TUTORIAL VIRTUAL MACHINE" in
Catalyst::Manual::Tutorial::01_Intro before doing the rest of this tutorial.
Although the tutorial should work correctly under most any recent version of
Perl running on any operating system, the tutorial has been written using the
virtual machine that is available for download. The entire tutorial has been
tested to be sure it runs correctly in this environment, so it is the most
trouble-free way to get started with Catalyst.
CREATE A NEW APPLICATION¶
The remainder of the tutorial will build an application called
"MyApp". First use the Catalyst "catalyst.pl" script to
initialize the framework for the "MyApp" application (make sure you
aren't still inside the directory of the "Hello" application from
the previous chapter of the tutorial or in a directory that already has a
"MyApp" subdirectory):
$ catalyst.pl MyApp
created "MyApp"
created "MyApp/script"
created "MyApp/lib"
created "MyApp/root"
...
created "MyApp/script/myapp_create.pl"
Change to application directory and Run "perl Makefile.PL" to make sure your install is complete
And change the "MyApp" directory the helper created:
$ cd MyApp
This creates a similar skeletal structure to what we saw in Chapter 2 of the
tutorial, except with "MyApp" and "myapp" substituted for
"Hello" and "hello". (As noted in Chapter 2, omit the
".pl" from the command if you are using Strawberry Perl.)
EDIT THE LIST OF CATALYST PLUGINS¶
One of the greatest benefits of Catalyst is that it has such a large library of
base classes and plugins available that you can use to easily add
functionality to your application. Plugins are used to seamlessly integrate
existing Perl modules into the overall Catalyst framework. In general, they do
this by adding additional methods to the "context" object (generally
written as $c) that Catalyst passes to every component throughout the
framework.
Take a look at the file "lib/MyApp.pm" that the helper created above.
By default, Catalyst enables three plugins/flags:
- •
- "-Debug" Flag
Enables the Catalyst debug output you saw when we started the
"script/myapp_server.pl" development server earlier. You can
remove this item when you place your application into production.
To be technically correct, it turns out that "-Debug" is not a
plugin, but a flag. Although most of the items specified on the
"use Catalyst" line of your application class will be plugins,
Catalyst supports a limited number of flag options (of these,
"-Debug" is the most common). See the documentation for
<https://metacpan.org/module/Catalyst|Catalyst.pm> to get details on
other flags (currently "-Engine", "-Home",
"-Log", and "-Stats").
If you prefer, there are several other ways to enable debug output:
- •
- the "$c->debug" method on the $c Catalyst context object
- •
- the "-d" option on the "script/myapp_server.pl"
script
- •
- the "CATALYST_DEBUG=1" environment variable (or
"CATALYST_DEBUG=0" to temporarily disable debug output)
TIP: Depending on your needs, it can be helpful to permanently remove
"-Debug" from "lib/MyApp.pm" and then use the
"-d" option to "script/myapp_server.pl" to re-enable it
when needed. We will not be using that approach in the tutorial, but feel free
to make use of it in your own projects.
- •
- 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 to the mix. To do this, edit
"lib/MyApp.pm" (this file is generally referred to as your
application class) and delete the lines with:
use Catalyst qw/
-Debug
ConfigLoader
Static::Simple
/;
Then replace it with:
# Load plugins
use Catalyst qw/
-Debug
ConfigLoader
Static::Simple
StackTrace
/;
Note: Recent versions of "Catalyst::Devel" have used a variety
of techniques to load these plugins/flags. For example, you might see the
following:
__PACKAGE__->setup(qw/-Debug ConfigLoader Static::Simple/);
Don't let these variations confuse you -- they all accomplish the same result.
This tells Catalyst to start using one additional plugin,
Catalyst::Plugin::StackTrace, to add a stack trace near the top of the
standard Catalyst "debug screen" (the screen Catalyst sends to your
browser when an error occurs). Be aware that StackTrace output appears in your
browser, not in the console window from which you're running your application,
which is where logging output usually goes.
Make sure when adding new plugins you also include them as a new dependency
within the Makefile.PL file. For example, after adding the StackTrace plugin
the Makefile.PL should include the following line:
requires 'Catalyst::Plugin::StackTrace';
Notes:
- •
- "__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), and the applications configuration.
Just don't forget to remove the die before you continue the
tutorial! :-)
CREATE A CATALYST CONTROLLER¶
As discussed earlier, controllers are where you write methods that interact with
user input. Typically, controller methods respond to "GET" and
"POST" requests from the user's web browser.
Use the Catalyst "create" script to add a controller for book-related
actions:
$ script/myapp_create.pl controller Books
exists "/home/catalyst/MyApp/script/../lib/MyApp/Controller"
exists "/home/catalyst/MyApp/script/../t"
created "/home/catalyst/MyApp/script/../lib/MyApp/Controller/Books.pm"
created "/home/catalyst/MyApp/script/../t/controller_Books.t"
Then edit "lib/MyApp/Controller/Books.pm" (as discussed in Chapter 2
of the Tutorial, Catalyst has a separate directory under "lib/MyApp"
for each of the three parts of MVC: "Model", "View" and
"Controller") and add the following method to the controller:
=head2 list
Fetch all book objects and pass to books/list.tt2 in stash to be displayed
=cut
sub list :Local {
# Retrieve the usual Perl OO '$self' for this object. $c is the Catalyst
# 'Context' that's used to 'glue together' the various components
# that make up the application
my ($self, $c) = @_;
# Retrieve all of the book records as book model objects and store in the
# stash where they can be accessed by the TT template
# $c->stash(books => [$c->model('DB::Book')->all]);
# But, for now, use this code until we create the model later
$c->stash(books => '');
# Set the TT template to use. You will almost always want to do this
# in your action methods (action methods respond to user input in
# your controllers).
$c->stash(template => 'books/list.tt2');
}
TIP: See Appendix 1 for tips on removing the leading spaces when cutting
and pasting example code from POD-based documents.
Programmers experienced with object-oriented Perl should recognize $self as a
reference to the object where this method was called. On the other hand, $c
will be new to many Perl programmers who have not used Catalyst before. This
is the "Catalyst Context object", and it is automatically passed as
the second argument to all Catalyst action methods. It is used to pass
information between components and provide access to Catalyst and plugin
functionality.
Catalyst Controller actions are regular Perl methods, but they make use of
attributes (the "":Local"" next to the ""sub
list"" in the code above) to provide additional information to the
Catalyst dispatcher logic (note that there can be an optional space between
the colon and the attribute name; you will see attributes written both ways).
Most Catalyst Controllers use one of five action types:
- •
- :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>). Other somewhat popular view
technologies include Mason (<
http://www.masonhq.com> and
<
http://www.masonbook.com>) and HTML::Template
(<
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 in Perl, there's more than one way to do it...).
Note: We will use "root/src" as the base directory for our
template files, with a full naming convention of
"root/src/_controller_name_/_action_name_.tt2". Another popular
option is to use "root/" as the base (with a full filename pattern
of "root/_controller_name_/_action_name_.tt2").
Create a TT Template Page¶
First create a directory for book-related TT templates:
$ mkdir -p root/src/books
Then create "root/src/books/list.tt2" in your editor and enter:
[% # This is a TT comment. -%]
[%- # Provide a title -%]
[% META title = 'Book List' -%]
[% # Note That the '-' at the beginning or end of TT code -%]
[% # "chomps" the whitespace/newline at that end of the -%]
[% # output (use View Source in browser to see the effect) -%]
[% # Some basic HTML with a loop to display books -%]
<table>
<tr><th>Title</th><th>Rating</th><th>Author(s)</th></tr>
[% # Display each book in a table row %]
[% FOREACH book IN books -%]
<tr>
<td>[% book.title %]</td>
<td>[% book.rating %]</td>
<td></td>
</tr>
[% END -%]
</table>
As indicated by the inline comments above, the "META title" line uses
TT's META feature to provide a title to the "wrapper" that we will
create later (and essentially does nothing at the moment). Meanwhile, the
"FOREACH" loop iterates through each "book" model object
and prints the "title" and "rating" fields.
The "[%" and "%]" tags are used to delimit Template Toolkit
code. TT supports a wide variety of directives for "calling" other
files, looping, conditional logic, etc. In general, TT simplifies the usual
range of Perl operators down to the single dot (".") operator. This
applies to operations as diverse as method calls, hash lookups, and list index
values (see Template::Manual::Variables for details and examples). In addition
to the usual Template::Toolkit module Pod documentation, you can access the TT
manual at <
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 and this external database model. Once you see how we can add
some powerful features to our DBIC model in Chapter 4, the elegance of this
approach will start to become more obvious.
NOTE: Older versions of Catalyst::Model::DBIC::Schema use the deprecated
DBIx::Class "load_classes" technique instead of the newer
"load_namespaces". For new applications, please try to use
"load_namespaces" since it more easily supports a very useful DBIC
technique called "ResultSet Classes." If you need to convert an
existing application from "load_classes" to
"load_namespaces," you can use this process to automate the
migration, but first make sure you have version 0.39 of
Catalyst::Model::DBIC::Schema and DBIx::Class::Schema::Loader version 0.05000
or later.
$ # Re-run the helper to upgrade for you
$ script/myapp_create.pl model DB DBIC::Schema MyApp::Schema \
create=static naming=current use_namespaces=1 \
dbi:SQLite:myapp.db \
on_connect_do="PRAGMA foreign_keys = ON"
ENABLE THE MODEL IN THE CONTROLLER¶
Open "lib/MyApp/Controller/Books.pm" and un-comment the model code we
left disabled earlier so that your version matches the following (un-comment
the line containing "[$c->model('DB::Book')->all]" and delete
the next 2 lines):
=head2 list
Fetch all book objects and pass to books/list.tt2 in stash to be displayed
=cut
sub list :Local {
# Retrieve the usual Perl OO '$self' for this object. $c is the Catalyst
# 'Context' that's used to 'glue together' the various components
# that make up the application
my ($self, $c) = @_;
# Retrieve all of the book records as book model objects and store
# in the stash where they can be accessed by the TT template
$c->stash(books => [$c->model('DB::Book')->all]);
# Set the TT template to use. You will almost always want to do this
# in your action methods (action methods respond to user input in
# your controllers).
$c->stash(template => 'books/list.tt2');
}
TIP: You may see the "$c->model('DB::Book')" un-commented
above written as "$c->model('DB')->resultset('Book')". The two
are equivalent. Either way, "$c->model" returns a
DBIx::Class::ResultSet which handles queries against the database and
iterating over the set of results that is returned.
We are using the "->all" to fetch all of the books. DBIC supports a
wide variety of more advanced operations to easily do things like filtering
and sorting the results. For example, the following could be used to sort the
results by descending title:
$c->model('DB::Book')->search({}, {order_by => 'title DESC'});
Some other examples are provided in "Complex WHERE clauses" in
DBIx::Class::Manual::Cookbook, with additional information found at
"search" in DBIx::Class::ResultSet, "Searching" in
DBIx::Class::Manual::FAQ, DBIx::Class::Manual::Intro and
Catalyst::Model::DBIC::Schema.
Test Run The Application¶
First, let's enable an environment variable that causes DBIx::Class to dump the
SQL statements used to access the database. This is a helpful trick when you
are trying to debug your database-oriented code. Press "Ctrl-C" to
break out of the development server and enter:
$ export DBIC_TRACE=1
$ script/myapp_server.pl -r
This assumes you are using bash as your shell -- adjust accordingly if you are
using a different shell (for example, under tcsh, use "setenv DBIC_TRACE
1").
NOTE: You can also set this in your code using
"$class->storage->debug(1);". See
DBIx::Class::Manual::Troubleshooting for details (including options to log to
a file instead of displaying to the Catalyst development server log).
Then launch the Catalyst development server. The log output should display
something like:
$ script/myapp_server.pl -r
[debug] Debug messages enabled
[debug] Statistics enabled
[debug] Loaded plugins:
.----------------------------------------------------------------------------.
| Catalyst::Plugin::ConfigLoader 0.30 |
| Catalyst::Plugin::StackTrace 0.11 |
'----------------------------------------------------------------------------'
[debug] Loaded dispatcher "Catalyst::Dispatcher"
[debug] Loaded engine "Catalyst::Engine"
[debug] Found home "/home/catalyst/MyApp"
[debug] Loaded Config "/home/catalyst/MyApp/myapp.conf"
[debug] Loaded components:
.-----------------------------------------------------------------+----------.
| Class | Type |
+-----------------------------------------------------------------+----------+
| MyApp::Controller::Books | instance |
| MyApp::Controller::Root | instance |
| MyApp::Model::DB | instance |
| MyApp::Model::DB::Author | class |
| MyApp::Model::DB::Book | class |
| MyApp::Model::DB::BookAuthor | class |
| MyApp::View::HTML | instance |
'-----------------------------------------------------------------+----------'
[debug] Loaded Private actions:
.----------------------+--------------------------------------+--------------.
| Private | Class | Method |
+----------------------+--------------------------------------+--------------+
| /default | MyApp::Controller::Root | default |
| /end | MyApp::Controller::Root | end |
| /index | MyApp::Controller::Root | index |
| /books/index | MyApp::Controller::Books | index |
| /books/list | MyApp::Controller::Books | list |
'----------------------+--------------------------------------+--------------'
[debug] Loaded Path actions:
.-------------------------------------+--------------------------------------.
| Path | Private |
+-------------------------------------+--------------------------------------+
| / | /default |
| / | /index |
| /books | /books/index |
| /books/list | /books/list |
'-------------------------------------+--------------------------------------'
[info] MyApp powered by Catalyst 5.80020
HTTP::Server::PSGI: Accepting connections at http://0:3000
NOTE: Be sure you run the "script/myapp_server.pl" command from
the 'base' directory of your application, not inside the "script"
directory itself or it will not be able to locate the "myapp.db"
database file. You can use a fully qualified or a relative path to locate the
database file, but we did not specify that when we ran the model helper
earlier.
Some things you should note in the output above:
- •
- 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.
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 classes (one for each of the Result Classes we
created).
Then hit the URL <
http://localhost:3000/books/list> with your browser and
be sure that the book list still displays correctly.
Note: You will not see the authors yet because the view isn't taking
advantage of these relationships. Read on to the next section where we update
the template to do that.
UPDATING THE VIEW¶
Let's add a new column to our book list page that takes advantage of the
relationship information we manually added to our schema files in the previous
section. Edit "root/src/books/list.tt2" and replace the
"empty" table cell "<td></td>" with the
following:
...
<td>
[% # NOTE: See Chapter 4 for a better way to do this! -%]
[% # First initialize a TT variable to hold a list. Then use a TT FOREACH -%]
[% # loop in 'side effect notation' to load just the last names of the -%]
[% # authors into the list. Note that the 'push' TT vmethod doesn't return -%]
[% # a value, so nothing will be printed here. But, if you have something -%]
[% # in TT that does return a value and you don't want it printed, you -%]
[% # 1) assign it to a bogus value, or -%]
[% # 2) use the CALL keyword to call it and discard the return value. -%]
[% tt_authors = [ ];
tt_authors.push(author.last_name) FOREACH author = book.authors %]
[% # Now use a TT 'virtual method' to display the author count in parens -%]
[% # Note the use of the TT filter "| html" to escape dangerous characters -%]
([% tt_authors.size | html %])
[% # Use another TT vmethod to join & print the names & comma separators -%]
[% tt_authors.join(', ') | html %]
</td>
...
IMPORTANT NOTE: Again, you should keep as much "logic code" as
possible out of your views. This kind of logic belongs in your model (the same
goes for controllers -- keep them as "thin" as possible and push all
of the "complicated code" out to your model objects). Avoid code
like you see in the previous example -- we are only using it here to show some
extra features in TT until we get to the more advanced model features we will
see in Chapter 4 (see "EXPLORING THE POWER OF DBIC" in
Catalyst::Manual::Tutorial::04_BasicCRUD).
Then hit "Reload" in your browser (note that you don't need to reload
the development server or use the "-r" option when updating TT
templates) and you should now see the number of authors each book has along
with a comma-separated list of the authors' last names. (If you didn't leave
the development server running from the previous step, you will obviously need
to start it before you can refresh your browser window.)
If you are still running the development server with "DBIC_TRACE"
enabled, you should also now see five more "SELECT" statements in
the debug output (one for each book as the authors are being retrieved by
DBIx::Class):
SELECT me.id, me.title, me.rating FROM book me:
SELECT author.id, author.first_name, author.last_name FROM book_author me
JOIN author author ON author.id = me.author_id WHERE ( me.book_id = ? ): '1'
SELECT author.id, author.first_name, author.last_name FROM book_author me
JOIN author author ON author.id = me.author_id WHERE ( me.book_id = ? ): '2'
SELECT author.id, author.first_name, author.last_name FROM book_author me
JOIN author author ON author.id = me.author_id WHERE ( me.book_id = ? ): '3'
SELECT author.id, author.first_name, author.last_name FROM book_author me
JOIN author author ON author.id = me.author_id WHERE ( me.book_id = ? ): '4'
SELECT author.id, author.first_name, author.last_name FROM book_author me
JOIN author author ON author.id = me.author_id WHERE ( me.book_id = ? ): '5'
Also note in "root/src/books/list.tt2" that we are using "|
html", a type of TT filter, to escape characters such as < and > to
< 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 be
found in the documentation for Template::Filters. (While we are on the topic
of security and escaping of dangerous values, one of the advantages of using
tools like DBIC for database access or HTML::FormFu for form management [see
Chapter 9] is that they automatically handle most escaping for you and
therefore dramatically increase the security of your app.)
RUNNING THE APPLICATION FROM THE COMMAND LINE¶
In some situations, it can be useful to run your application and display a page
without using a browser. Catalyst lets you do this using the
"script/myapp_test.pl" script. Just supply the URL you wish to
display and it will run that request through the normal controller dispatch
logic and use the appropriate view to render the output (obviously, complex
pages may dump a lot of text to your terminal window). For example, if
"Ctrl+C" out of the development server and then type:
$ script/myapp_test.pl "/books/list"
You should get the same text as if you visited
<
http://localhost:3000/books/list> with the normal development server
and asked your browser to view the page source. You can even pipe this HTML
text output to a text-based browser using a command like:
$ script/myapp_test.pl "/books/list" | lynx -stdin
And you should see a fully rendered text-based view of your page. (If you are
following along in Debian 6, type "sudo aptitude -y install lynx" to
install lynx.) If you do start lynx, you can use the "Q" key to
quit.
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).
#$c->stash(template => 'books/list.tt2');
}
You should now be able to access the <
http://localhost:3000/books/list>
URL as before.
NOTE: If you use the default template technique, you will
not be
able to use either the "$c->forward" or the
"$c->detach" mechanisms (these are discussed in Chapter 2 and
Chapter 9 of the Tutorial).
IMPORTANT: Make sure that you do
not skip the following section
before continuing to the next chapter 4 Basic CRUD.
Return To A Manually Specified Template¶
In order to be able to use "$c->forward" and
"$c->detach" later in the tutorial, you should remove the comment
from the statement in "sub list" in
"lib/MyApp/Controller/Books.pm":
$c->stash(template => 'books/list.tt2');
Then delete the "TEMPLATE_EXTENSION" line in
"lib/MyApp/View/HTML.pm".
Check the <
http://localhost:3000/books/list> URL in your browser. It
should look the same manner as with earlier sections.
You can jump to the next chapter of the tutorial here: Basic CRUD
AUTHOR¶
Kennedy Clark, "hkclark@gmail.com"
Feel free to contact the author for any errors or suggestions, but the best way
to report issues is via the CPAN RT Bug system at
<
https://rt.cpan.org/Public/Dist/Display.html?Name=Catalyst-Manual>.
Copyright 2006-2011, Kennedy Clark, under the Creative Commons Attribution
Share-Alike License Version 3.0
(<
http://creativecommons.org/licenses/by-sa/3.0/us/>).