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+---
+title: A simple feed aggregator with modern Perl - part 1
+category: perl
+layout: post
+---
+
+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":http://search.cpan.org/~drolsky/Moose-0.75/lib/Moose.pm, "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 github account at the
+same time each article is published.
+
+bc. disclaimer:
+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.
+
+
+h3. 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.
+
+bc. 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.
+
+{% highlight bash %}
+module-setup MyModel
+cd MyModel
+vim lib/MyModel.pm
+{% endhighlight %}
+
+{% highlight perl %}
+package MyModel;
+use base qw/DBIx::Class::Schema/;
+__PACKAGE__->load_classes();
+1;
+{% endhighlight %}
+
+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*:
+
+{% highlight 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;
+{% endhighlight %}
+
+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*:
+
+{% highlight 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;
+{% endhighlight %}
+
+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:
+
+{% highlight 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'
+    },
+);
+{% endhighlight %}
+
+*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:
+
+{% highlight perl %}
+sub sqlt_deploy_hook {
+    my ($self, $sqlt_table) = @_;
+    $sqlt_table->extra(
+        mysql_table_type => 'InnoDB',
+        mysql_charset    => 'utf8'
+    );
+}
+{% endhighlight %}
+
+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:
+
+{% highlight 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';
+}
+{% endhighlight %}
+
+This script will deploy for you the schema (you need to create the database first if using with mysql).
+
+Executing the following command:
+
+{% highlight bash %}
+perl bin/deploy_mymodel.pl --dsn dbi:SQLite:model.db
+{% endhighlight %}
+
+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.
+
+"link to the code":http://github.com/franckcuny/ironman-mymodel/tree/master
+
+bc. 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.