Tuesday, 3 November 2009

Building a data access layer

I recently agreed to help a student out with a software development assignment out for university. At first glance, it looks to be a pretty heavyweight peice of work for an undergrad to be given, even more so when the undergrad doesnt have a lot of experience in software development.

Essentially, the assignment is to create an Ebay-esque Windows Form app. The wording of the assignment makes it look harder than it actually is, when you get around the features that are being requested the actual technical requirement is really very simple. The assignment needs to be split into several peices, something that a lot of students probably wont be familiar with as it simply doesnt get taught at uni. The first section is the persistent data storage, I don't yet know what options are available at the moment, but the assignment spec asks for data to be retrieved from either a database or some XML. Now, I can understand why these features would be requested, it allows the application to be able to pick up its data from the local infrastructure or from a web service.

So, they key technical part here? Well, it's a data access layer. I have put together a few of these now, normally as part of an architectural migration to ease the switch over, all this assignment really needs is an appropriate DAL in order to get its data into the Windows app. It struck me that there really isnt a lot of info on how to do this rather simple thing, I think with the maturation of ORM like nHibernate and Linq-to-SQL a lot of people are over looking this for smaller projects. Anyway, I plan to put together a short howto on building your own DAL, because once you understand how the things work in the firs place, it makes implementing your own or using one of the ORM's already out there a lot more intuitive.