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Upgrading to Catalyst 5.8

Over the last few days at $work I’ve been upgrading Catalyst from 5.7 to 5.8. This new version of catalyst, released in April, has been completely overhauled to use Moose for it’s OO system, among other enhancements and bug fixes.

I found that the Catalyst::Manual::CatalystAndMoose manual was a great starting point to using Moose with Catalyst. Also, Catalyst::Upgrading has specific points to consider when upgrading to 5.8. During the initial install of Catalyst 5.8 I was told that I had a few related modules installed, that while not Catalyst prerequisites, I should upgrade them as they were known to fail on the new Catalyst. I was lucky that I caught this message, as cpan did not pause to wait for me to read it and went on its marry way building, testing, and installing Catalyst.

Once installed I went ahead and also upgraded some related modules we use such as Catalyst::Plugin::Authentication, DBIx::Class, Catalyst::Plugin::Session, Catalyst::Authentication::Store::DBIx::Class, etc. This way I could test all these upgrades all at once instead of one at a time.

Next I modified all my custom plugins to use MRO::Compat instead of Class::C3 per the documentation in Class::C3::Adopt::NEXT. But, then I realized I might as well just rewrite all my plugins as Moose::Roles as its pretty easy to convert a plugin to a role and you end up with much cleaner code.

I started Apache up and things mostly worked. There were a few backwards incompatibilities that I wasn’t aware of, such as there were a few cases where developers had done this:

Instead of:

In our previous version of catalyst (5.7) using :Local, while not documented, worked just like :Private if the subroutine was named index. In 5.8 only :Private will cause a handler named index to be the default handler if the URL resolves to the controller only. This was an easy fix. There were a couple other small issues, but nothing major. I found and fixed a bug in Catalyst::Model::DBIC::Schema and added the support for the compute() method to Catalyst::Plugin::Cache. Both of these changes reduced the amount of changes I needed to make to my own code.

A couple hours in to it I was upgraded and everything was working. Of course I spent the next few days upgrading/enhancing/rewriting Catalyst bits that could be done much more elegantly, and with less code, using Moose.

On a side note, during the upgrade I found this great quote in Catalyst::Model::Adaptor:

Catalyst is glue, not a way of life!

Amen! Most people, myself included, start out by writing all their business logic in their Controllers because that is what MVC told them to do. Don’t do it! Catalyst is meant to be a GLUE – most of your application should be written in a way that it doesn’t give a flying crap how, or by whom, it is used. Put your business logic in modules that optionally expose themselves as Models (perhaps via Catalyst::Model::Adaptor) or just by adding a use statement in your controller that then uses that module. Your controllers should be little more than code to glue a data source with the view and provide some input validation.

I’ve been waiting a long time for this Moosification and its been a joy working with this new Catalyst. Next up to bat will be the Moosification of DBIx::Class! Think we’ll get it by Christmas? :)

Don’t forget to buy the new Catalyst Book! If purchasing from Amazon make sure you follow this link to ensure that the Enlightened Perl Organisation gets a cut of the sale.