Friday, 4 May 2012

My “Agile SQL Tweet” Slide

Before I put the PowerPoint slides for my ACCU conference talk on Database Development Using TDD up on my web site I agonised over whether to remove the 3rd slide or not. The slide in question just contains the following tweet from Allan Kelly:-

@chrisoldwood is the only person I know with a convincing Agile SQL story -- @allankelly

I felt that viewing the slide in isolation would only amplify the arrogance which could be attached to it and that wouldn’t have a positive effect. But at the same time I felt I should put up what was shown and accept that perhaps it may also raise the same questions that I had that caused me to put it in the first place.

The slide forms part of the prologue and was originally just a picture of myself to act as a backdrop whilst I spent a couple of minutes describing who I was and what I did as I’m not a database developer per-se, I’m mostly a C#/C++ service layer guy who has slipped into the SQL arena like many similar developers. As a consequence I have tried to work with the RDBMS in the same way that I would approach anything else, by using TDD and abstracting the client from the underlying implementation. So, rather than couple the client and database code tightly with client-side SQL[*] I have kept them decoupled to allow the database to develop (and therefore be refactored) independently where possible - I don’t expose public fields in my types[#] so why directly expose tables?

And then this tweet from Allan Kelly appeared. Until that moment I suspected I was the proverbial square peg trying desperately to fit into a round hole, but maybe, just maybe, I might not be barking mad after all. There are many benefits to TDD (and unit testing in particular) over and above proving the functional correctness of a piece of code, but I don’t understand why more people can’t see that.

So the slide should hopefully provoke a reaction that forces you to question what your database development tools and processes are and whether you’re getting the most out of them. If you are then great, it’s working for you, but if you have that uneasy feeling that you’re stymied at every turn because your database can’t evolve quickly enough then perhaps what you’re about to see (and hear, if you attended) will provide food-for-thought about what you could change.

Prior to this the most ‘positive’ reaction I’ve had to what I’ve been suggesting is:-

“I suppose it makes sense, I’ve just never seen it done like that before”

[*] I’m not just talking about explicit embedded SQL here where the SQL code is a string literal (or as a format string) but also where it is implicit as a by-product of a technology such as LINQ-to-SQL. One way or another the schema is likely to be too tightly coupled to the calling code and that means your database design will be harder to change as will remediating performance problems.

[#] Some would argue that a DTO (Data Transfer Object) does exactly that, but a modern RDBMS is so much more than just a data persistence mechanism. Use its power where it makes sense to.

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