path: root/_posts/2009-05-13-a-simple-feed-aggregator-with-modern-perl-part-4.textile

---
layout: post
title: A simple feed aggregator with modern Perl - part 4
category: perl
---

We have the model, the aggregator (and some tests),  now we can do a basic frontend to read our feed. For this I will create a webapp using "catalyst":http://www.catalystframework.org.

"Catalyst::Devel":http://search.cpan.org/perldoc?Catalyst::Devel is required for developping catalyst application, so we will install it first:

{% highlight perl %}
cpan Catalyst::Devel
{% endhighlight %}

Now we can create our catalyst application using the helper:

{% highlight perl %}
catalyst.pl MyFeedReader
{% endhighlight %}

This command initialise the framework for our application *MyFeedReader*. A number of files are created, like the structure of the MVC directory, some tests, helpers, ...

We start by creating a view, using "TTSite":http://search.cpan.org/perldoc?Catalyst::View::TT. TTSite generate some templates for us, and the configuration for this template. We will also have a basic CSS, a header, footer, etc.

{% highlight bash %}
cd MyFeedReader
perl script/myfeedreader_create.pl view TT TTSite
{% endhighlight %}

TTSite files are under *root/src* and *root/lib*. A *MyAggregator/View/TT.pm* file is also created. We edit it to make it look like this:

{% highlight perl %}
__PACKAGE__->config({
    INCLUDE_PATH => [
        MyFeedReader->path_to( 'root', 'src' ),
        MyFeedReader->path_to( 'root', 'lib' )
    ],
    PRE_PROCESS  => 'config/main',
    WRAPPER      => 'site/wrapper',
    ERROR        => 'error.tt2',
    TIMER        => 0,
    TEMPLATE_EXTENSION => '.tt2',
});
{% endhighlight %}

Now we create our first template, in *root/src/index.tt2*

bq. to <a href="/feed/">your feeds</a>

If you start the application (using _perl script/myfeedreader_server.pl_) and point your browser on http://localhost:3000/, this template will be rendered.

We need two models, one for KiokuDB and another one for MyModel:

*lib/MyFeedReader/Model/KiokuDB.pm*

{% highlight perl %}
package MyFeedReader::Model::KiokuDB;
use Moose;
BEGIN { extends qw(Catalyst::Model::KiokuDB) }
1;
{% endhighlight %}

we edit the configuration file (*myfeedreader.conf*), and set the dsn for our kiokudb backend

{% highlight perl %}
    <Model KiokuDB>
        dsn dbi:SQLite:../MyAggregator/foo.db
    </Model>
{% endhighlight %}

*lib/MyFeedReader/Model/MyModel.pm*

{% highlight perl %}
package MyFeedReader::Model::MyModel;
use base qw/Catalyst::Model::DBIC::Schema/;
1;
{% endhighlight %}

and the configuration:

{% highlight perl %}
<Model MyModel>
    connect_info dbi:SQLite:../MyModel/model.db
    schema_class MyModel
</Model>
{% endhighlight %}

We got our view and our model, we can do the code for the controller. We need 2 controller, one for the feed, and one for the entries. The Feed controller will list them and display entries titles for a given feed. The Entry controller will just display them.

*lib/MyFeedReader/Controller/Feed.pm*

{% highlight perl %}
package MyFeedReader::Controller::Feed;
use strict;
use warnings;
use parent 'Catalyst::Controller';

__PACKAGE__->config->{namespace} = 'feed';

sub index : Path : Args(0) {
    my ( $self, $c ) = @_;
    $c->stash->{feeds}
        = [ $c->model('MyModel')->resultset('Feed')->search() ];
}

sub view : Chained('/') : PathPart('feed/view') : Args(1) {
    my ( $self, $c, $id ) = @_;
    $c->stash->{feed}
        = $c->model('MyModel')->resultset('Feed')->find($id);
}

1;
{% endhighlight %}

The function *index* list the feeds, while the function *view* list the entries for a give feed. We use the chained action mechanism to dispatch this url, so we can have urls like this _/feed/*_

We create our 2 templates (for index and view):

*root/src/feed/index.tt2*

{% highlight perl %}
<ul>
    [% FOREACH feed IN feeds %]
        <li><a href="/feed/view/[% feed.id %]">[% feed.url %]</a></li>
    [% END %]
</ul>
{% endhighlight %}

*root/src/feed/vew.tt2*

{% highlight perl %}
<h1>[% feed.url %]</h1>

<h3>entries</h3>
<ul>
    [% FOREACH entry IN feed.entries %]
        <li><a href="/entry/[% entry.id %]">[% entry.permalink %]</a></li>
    [% END %]
</ul>
{% endhighlight %}

If you point your browser to

bc. http://localhost:3000/feed/

you will see this:

!/static/imgs/list_feed.png(list feeds)!

Now the controller for displaying the entries:

{% highlight perl %}
package MyFeedReader::Controller::Entry;
use strict;
use warnings;
use MyAggregator::Entry;
use parent 'Catalyst::Controller';

__PACKAGE__->config->{namespace} = 'entry';

sub view : Chained('/') : PathPart('entry') : Args(1) {
    my ( $self, $c, $id ) = @_;
    $c->stash->{entry} = $c->model('KiokuDB')->lookup($id);
}

1;
{% endhighlight %}

The function *view* fetch an entry from the kiokudb backend, and store it in the stash, so we can use it in our template.

*root/src/entry/view.tt2*

{% highlight perl %}
<h1><a href="[% entry.permalink %]">[% entry.title %]</a></h1>
<span>Posted [% entry.date %] by [% entry.author %]</span>
<div id="content">
    [% entry.content %]
</div>
{% endhighlight %}

If you point your browser to an entry (something like *http://localhost:3000/entry/somesha256value*), you will see an entry:

!/static/imgs/show_entry.png(show entry)!

Et voila, we are done with a really basic feed reader. You can add methods to add or delete feed, mark an entry as read, ...

"The code is available on github":http://github.com/franckcuny/ironman-myfeedreader/tree/master