Recently, I’ve been asked to add tagging to the guided reports section. I used this as an opportunity to implement a mixin that’s similar in spirit to acts_as_taggable for Ruby’s ActiveRecord ORM.

I called this class, “C4::Taggable”, and it will inject tagging-related methods to any class that uses it. Normally, it’s bad form to use Exporter in OO code, but that mainly applies to when you’re defining a class. However, when you’re defining a mixin, I believe the use of Exporter is justified, because it’s one of the easiest ways to inject methods into a namespace.

To illustrate this technique, here is an outline of how C4::Taggable is implemented. (For brevity’s sake, the method bodies were omitted.)

C4::Taggable

  package C4::Taggable;
  use strict;
  use warnings;
  use base 'Exporter';
  use C4::Context;
  our @EXPORT_OK   = qw( add_tag remove_tag tags search_by_tags                );
  our %EXPORT_TAGS =   ( mixin => [qw(add_tag remove_tag tags search_by_tags)] );

  sub add_tag        { }
  sub remove_tag     { }
  sub tags           { }
  sub search_by_tags { }

  1;

Notice how C4::Taggable exports tagging-related methods.

Next, C4::Report is outlined. Note that by using C4::Taggable, C4::Report became taggable by virtue of having tagging-related methods for C4::Taggable being mixed into it.

C4::Report

  package C4::Report;
  use strict;
  use warnings;
  use C4::Context;
  use C4::Taggable ':mixin';

  sub new            { }
  sub id             { }
  sub borrowernumber { }
  sub date_created   { }
  sub last_modified  { }
  sub savedsql       { }
  sub last_run       { }
  sub report_name    { }
  sub type           { }
  sub notes          { }
  sub update         { }

  sub table          { }

  1;

Isn’t that simple? Now any time you want to add tagging to a class, you just use C4::Taggable.

What’s the catch?

The catch is that C4::Taggable will have expectations about the host class and the database schema. The host class has to provide a few methods so that C4::Taggable can introspect enough to generate the right SQL. There will also be a table you have to create that has a predefined structure and naming pattern. I won’t go into any more detail here, but suffice it to say that for C4::Taggable to work, certain conventions have to be followed.

To me, it’s a small price to pay, because it makes it ridiculously easy to add tagging to other classes should that ever be necessary or desired.

This entry was posted on Monday, May 18th, 2009 at 11:39 am by john.beppu and is filed under APIs, Koha, Perl, Tips & Tricks. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.