+---

+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.