----

-date: 2009-04-27T00:00:00Z

-summary: In which I write a feed aggregator in Perl.

-title: A simple feed aggregator with modern Perl - part 1

----

-

-Following [Matt's post](http://www.shadowcat.co.uk/blog/matt-s-trout/iron-man/) about people not blogging enough about Perl, I've decided to try to post once a week about Perl. So I will start by a series of articles about what we call **modern Perl**. For this, I will write a simple feed agregator (using [Moose](https://metacpan.org/pod/Moose), [DBIx::Class](http://search.cpan.org/perldoc?DBIx::Class), [KiokuDB](http://search.cpan.org/perldoc?KiokuDB), some tests, and a basic frontend (with [Catalyst](http://search.cpan.org/perldoc?Catalyst)). This article will be split in four parts:

-

- * the first one will explain how to create a schema using **DBIx::Class**

- * the second will be about the aggregator. I will use **Moose*** and **KiokuDB**

- * the third one will be about writing tests with **Test::Class**

- * the last one will focus on **Catalyst**

-

-The code of these modules will be available on [my git server](http://git.lumberjaph.net/) at the same time each article is published.

-

-> I'm not showing you how to write the perfect feed aggregator. The purpose of this series of articles is only to show you how to write a simple aggregator using modern Perl.

-

-### The database schema

-

-We will use a database to store a list of feeds and feed entries. As I don't like, no, wait, I *hate* SQL, I will use an ORM for accessing the database. For this, my choice is **DBIx::Class**, the best ORM available in Perl.

-

-> If you never have used an ORM before, ORM stands for Object Relational Mapping. It's a SQL to OO mapper that creates an abstract encapsulation of your databases operations. **DBIx::Class**' purpose is to represent "queries in your code as perl-ish as possible.

-

-For a basic aggregator we need:

-

- * a table for the list of feeds

- * a table for the entries

-

-We will create these two tables using *DBIx::Class*. For this, we first create a Schema module. I use *Module::Setup*, but you can use **Module::Starter** or whatever you want.

-

-```bash

-% module-setup MyModel

-% cd MyModel

-% vim lib/MyModel.pm

-```

-

-```perl

-package MyModel;

-use base qw/DBIx::Class::Schema/;

-__PACKAGE__->load_classes();

-1;

-```

-

-So, we have just created a schema class. The **load_classes** method loads all the classes that reside under the **MyModel** namespace. We now create the result class **MyModel::Feed** in **lib/MyModel/Feed.pm**:

-

-```perl

-package MyModel::Feed;

-use base qw/DBIx::Class/;

-__PACKAGE__->load_components(qw/Core/);

-__PACKAGE__->table('feed');

-__PACKAGE__->add_columns(qw/ feedid url /);

-__PACKAGE__->set_primary_key('feedid');

-__PACKAGE__->has_many(entries => 'MyModel::Entry', 'feedid');

-1;

-```

-

-Pretty self explanatory: we declare a result class that uses the table feed, with two columns: **feedid** and **url**, **feedid** being the primary key. The **has_many** method declares a one-to-many relationship.

-

-Now the result class **MyModel::Entry** in **lib/MyModel/Entry.pm**:

-

-```perl

-package MyModel::Entry;

-use base qw/DBIx::Class/;

-__PACKAGE__->load_components(qw/Core/);

-__PACKAGE__->table('entry');

-__PACKAGE__->add_columns(qw/ entryid permalink feedid/);

-__PACKAGE__->set_primary_key('entryid');

-__PACKAGE__->belongs_to(feed => 'MyModel::Feed', 'feedid');

-1;

-```

-

-Here we declare **feed** as a foreign key, using the column name **feedid**.

-

-You can do a more complex declaration of your schema. Let's say you want to declare the type of your fields, you can do this:

-

-```perl

-__PACKAGE__->add_columns(

- 'permalink' => {

- 'data_type' => 'TEXT',

- 'is_auto_increment' => 0,

- 'default_value' => undef,

- 'is_foreign_key' => 0,

- 'name' => 'url',

- 'is_nullable' => 1,

- 'size' => '65535'

- },

-);

-```

-

-**DBIx::Class** also provides hooks for the deploy command. If you are using MySQL, you may need a InnoDB table. In your class, you can add this:

-

-```perl

-sub sqlt_deploy_hook {

- my ($self, $sqlt_table) = @_;

- $sqlt_table->extra(

- mysql_table_type => 'InnoDB',

- mysql_charset => 'utf8'

- );

-}

-```

-

-Next time you call deploy on this table, the hook will be sent to **SQL::Translator::Schema**, and force the type of your table to InnoDB, and the charset to utf8.

-

-Now that we have a **DBIx::Class** schema, we need to deploy it. For this, I always do the same thing: create a **bin/deploy_mymodel.pl** script with the following code:

-

-```perl

-use strict;

-use feature 'say';

-use Getopt::Long;

-use lib('lib');

-use MyModel;

-

-GetOptions(

- 'dsn=s' => \my $dsn,

- 'user=s' => \my $user,

- 'passwd=s' => \my $passwd

-) or die usage();

-

-my $schema = MyModel->connect($dsn, $user, $passwd);

-say 'deploying schema ...';

-$schema->deploy;

-

-say 'done';

-

-sub usage {

- say

- 'usage: deploy_mymodel.pl --dsn $dsn --user $user --passwd $passwd';

-}

-```

-

-This script will deploy for you the schema (you need to create the database first if using with mysql).

-

-Executing the following command `perl bin/deploy_mymodel.pl --dsn dbi:SQLite:model.db` will generate a **model.db** database so we can work and test it. Now that we got our (really) simple **MyModel** schema, we can start to hack on our aggregator.

-

-[The code is available on my git server](http://git.lumberjaph.net/p5-ironman-mymodel.git/).

-

-> while using **DBIx::Class**, you may want to take a look at the generated queries. For this, export `DBIC_TRACE=1` in your environment, and the queries will be printed on STDERR.