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Building E-Commerce Sites with Handel

by Christopher H. Laco
November 17, 2005

Over the years of doing various levels of web-based programming, I've come feel like Dante taking a trip through the nine circles of web programmer hell. There are certain things we must endure over and over, from project to project, that seem to take an exorbitant amount of coding to accomplish with little forward progress on the actual project itself. Some of these circles invariably include HTML forms, form validation code, time translation or formatting code, Unicode or encoding code, and, since the dot-com boom, shopping cart/checkout code.

While the CPAN community has solved most of the problems quite nicely with modules like Data::FormValidator, HTML::FillInForm, DateTime, and the various FromForm/QuickForm/FormBuilder modules, I still yearned for a lightweight, straightforward shopping cart module that didn't involve installed an entire CMS or B2B solution. Thus, Handel.

Later I will show you how to get a functional shopping cart up and running using no lines of code. You heard that correctly: no lines of code. Zero. None. Nada.

What Handel Is

Handel is a set of modules to perform the repetitive tasks associated with creating a shopping cart and a checkout process on the Web in Perl.

This includes the usual actions, such as adding items to the cart, updating item quantity, and removing items, as well as less common features, including saving the current contents of the cart to a wish list and restoring wish lists back into the current shopping cart.

Handel doesn't just provide shopping carts. It has order add/update features, taglib support for AxKit, plugin support for Template Toolkit, and helper support for Catalyst. It also includes a plugin-based checkout processing pipeline where orders are passed through a step-by-step process that (with the right plugins loaded) can do anything from address validation and shipping calculation to credit-card verification and email/fax order confirmations.

What Handel Is Not

From the beginning, the two main goals of Handel were to be situation-agnostic and to be a set of building blocks, not an out-of-the-box solution.

Handel needed to be reusable from the standpoint that it should be able to interact with your shopping cart's contents and process an order from anywhere without rewriting the core set of data/processing code. It should be able to get the cart's contents from within a shell script, from a terminal app, from a web page, or from a web service. E-commerce isn't always just about putting up a website. Many times, there will be both a front-end, web-based system and a back-end, GUI-based application.

I also decided early on that shopping carts and checkout processes can't possibly be everything for everyone. While there are many things in common (part numbers and prices), every site has different requirements on how to process an order and the steps necessary to place that order. It is for this reason that the checkout process by itself does absolutely nothing, but instead employs the help of plugins to add requirements or features.

Getting Started

Before you start, you need to have a few things installed from CPAN. These include:

• Perl 5.8.1+
• Handel 0.26+
• Catalyst 5.33+
• Catalyst::View::TT
• HTML::FillInForm 1.04+
• Data::FormValidator 4.00+
• DBD::SQLite
• sqlite3

Perl 5.8.1 or greater? What about 5.6.x? Yeah, sorry. While Handel runs on Perl 5.6.1 or greater, Catalyst requires 5.8.1 or newer. That's a good thing. Now upgrade your Perl version! :-)

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