This is a continuation of the previous blog on the Perl DBIx
class....in essence this is to document my journey particularly
on the Object Relational Mapping (ORM) subject.
I am actually going further than simply exploring a
simple model for a bookshop ala Amazon or BarnesAndNoble.com,
but would take it further on how to use the Model in the
spirit of the Web development particularly how we can
incorporate the model with the venerable Perl Catalyst MVC (Model
View Controller) framework.
Catalyst MVC
One thing that draws me to the world of Perl for the past 7+ years is
the premise that "There is more than one way to do it".
I find that there are both beauty and dangers in that premise.
For industry that replete with the term of "best practices", that premise
would run contrary to the mantra. As for me, best practices is a journey
and never cast in stone. As for any journey, one has to begin with a single
step and would make lots of mistakes. For some mistakes are something to frown upon.
For me personally, mistakes are part of life. They are the springboard to get better,
to be more concise, more elegant, and more productive.
I find that beauty in Perl, Python and quite recently Ruby (for the past 3+ years anyway).
But I digress....if you want to conquer anything, software development or otherwise,
you need the right tools. For Web and Web 2.0 development, you would most likely
encounter the issues of CRUD (Create, Read, Update, and Delete).
and if you are thinking about leveraging Perl for your Web development needs, then looks no
further than Catalyst MVC.
Step 1
Fire up catalyst .....I name my app as mybookshop
let us start by defining and working with the Model straight from SQL to the DBIx Class Schema
The Model
Pretty simple and straightforward. Now we are going to use SQLite3
as the backend DB.
if you save the above DDL as books.sql then use the following command
to generate the SQLite3 DB:
cat books.sql | sqlite3 books.db
and use the DBIx Class Loader make_schema_at utilities to come up with
schema for the Books, Authors, and Categories:
here is the script that I have used in the command line to come up with
those schemas above
perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir=. -e 'make_schema_at("MyBookShop::Schema", {debug => 1}, ["dbi:SQLite:dbname:books.db","",""])'
If you would like further information, you can consult the CPAN page directly
The DBIC Schema would look like as follows:
The Controller
Let us focus our attentions with the Books entity right now. Let us say that
we are going to display the books selection through the URL like this:
http://localhost:3000/books
http://localhost:3000/books/list
In order to do that, we need to create a Books controller through the command line:
perl script/mybookshop_create.pl controller Books
with the results of that the Books.pm (Perl module) is added under the Controller
directory.
The Books.pm, the Perl Module file, is where you are going to define and all the actions relating to the Books model..
Going back the list of URL(s) specified above, we want to use the "localhost/books/list" to display our books selections. In Catalyst parlance, we have to define a "list" method in order to accomplish the objective....and one example will be detailed as such:
Let us spend some time going over the code................
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
my $page = $c->req->param('page') || 1;
my $rows = $c->req->param('rows') || 3;
my $where = { };
my $attr = { page => $page, rows => $rows };
my $rs = $c->model('DBIC::Books')->search($where, $attr);
my $pager = $rs->pager();
$c->stash->{pager} = $pager;
$c->stash->{books} = [$rs->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';
}
The var. $c is for the Catalyst Controller, whereas the $c->req is the "HTTP" Request object.
We are going to incorporate pagination in our example, thus...we assume unless defined that
we are starting with page 1 and each page would only retrieve 3 items/results.
my $page = $c->req->param('page') || 1;
my $rows = $c->req->param('rows') || 3;
my $where = { };
my $attr = { page => $page, rows => $rows };
my $rs = $c->model('DBIC::Books')->search($where, $attr);
my $pager = $rs->pager();
We have to make the results available for the View, which is the next topic inline, by "saving" our resultsets in through stash
$c->stash->{pager} = $pager;
$c->stash->{books} = [$rs->all];
The View
Following along from the last section, the View comes into play in the following code section:
# 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';
The TT in this case stands for the Template Toolkit, which is one of the "View" frameworks that are popular within the Catalyst MVC.
Remember our "books" model that we save in the Controller module, as in the following code:
$c->stash->{books} = [$rs->all];
The "books" resultsets are manipulated in the View by the following code in the list.tt2 module
[% # Display each book in a table row %]
[% FOREACH book IN books -%]
[% book.name %]
[% book.rating %]
[% book.fk_author_id.name %]
[% END -%]
In case you are wondering where you specify the Template Toolkit files...they are usually under app/root/src directory...in my case it is specifically under mybookshop/root/src
Once everything is in place, you can explore more by starting the Catalyst server
So...play around...experiment...make mistakes...and get better :)...Remember...there is more than one way to do it :)
Let me know if you have any comments or questions....I will be more than happy to help in anyway I could.
