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diff --git a/posts/2009-04-27-a-simple-feed-aggregator-with-modern-perl-part-1.org b/posts/2009-04-27-a-simple-feed-aggregator-with-modern-perl-part-1.org new file mode 100644 index 0000000..efff473 --- /dev/null +++ b/posts/2009-04-27-a-simple-feed-aggregator-with-modern-perl-part-1.org @@ -0,0 +1,179 @@ +Following +[[http://www.shadowcat.co.uk/blog/matt-s-trout/iron-man/][Matt's post]] +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 [[https://metacpan.org/pod/Moose][Moose]], +[[http://search.cpan.org/perldoc?DBIx::Class][DBIx::Class]], +[[http://search.cpan.org/perldoc?KiokuDB][KiokuDB]], some tests, and a +basic frontend (with +[[http://search.cpan.org/perldoc?Catalyst][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 +[[http://git.lumberjaph.net/][my git server]] at the same time each +article is published. + +#+BEGIN_QUOTE + 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. +#+END_QUOTE + +*** 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. + +#+BEGIN_QUOTE + 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. +#+END_QUOTE + +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. + +#+BEGIN_EXAMPLE + % module-setup MyModel + % cd MyModel + % vim lib/MyModel.pm +#+END_EXAMPLE + +#+BEGIN_SRC perl + package MyModel; + use base qw/DBIx::Class::Schema/; + __PACKAGE__->load_classes(); + 1; +#+END_SRC + +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*: + +#+BEGIN_SRC 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; +#+END_SRC + +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*: + +#+BEGIN_SRC 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; +#+END_SRC + +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: + +#+BEGIN_SRC 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' + }, + ); +#+END_SRC + +*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: + +#+BEGIN_SRC perl + sub sqlt_deploy_hook { + my ($self, $sqlt_table) = @_; + $sqlt_table->extra( + mysql_table_type => 'InnoDB', + mysql_charset => 'utf8' + ); + } +#+END_SRC + +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: + +#+BEGIN_SRC 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'; + } +#+END_SRC + +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. + +[[http://git.lumberjaph.net/p5-ironman-mymodel.git/][The code is +available on my git server]]. + +#+BEGIN_QUOTE + 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. +#+END_QUOTE |