james mckay dot net
because there are few things that are less logical than business logic

It’s not just an opinion, it’s scar tissue

Software developers such as myself often have strong opinions about how code should be written. While some people may be tempted to dismiss these as “just an opinion,” the truth of the matter is that more often than not, these strong opinions are forged in the fires of Things Going Wrong And Having To Clear Up Afterwards.

Take exception handling for example. Bad exception handling practices are one of my big bugbears in code. Whether it’s Pokémon exception handling, or advocating return codes instead of exceptions, or just incoherent or unclear guidelines about how to use them, bad error handling really, really gets up my nose.

The project that you have to thank for that is called Bills Knowledge Base.

Bills Knowledge Base, or BKB as it was affectionately known, was an internal web application in Parliament used to keep track of the progress of legislation. When I was brought onto the project in early 2009, it had all of a sudden stopped displaying any data. And I was asked to fix it. NOW.

It quickly became clear why this was the case. Someone had just deployed a new version and had missed out an important DLL. The reason why it wasn’t showing any data instead of crashing out with a stack trace or an error page was that it was riddled with Pokémon exception handling. All over the place. Put there by some code generation for which the templates had been thrown away.

Having deployed the missing DLL, I then turned my attention to the database.

It probably won’t surprise you when I tell you that it was a complete mess. Foreign key constraints were missing, leaving orphaned rows everywhere. Dates were stored in text fields in a whole array of mutually incompatible formats. Fields that were supposed to be required were blank. Enumeration fields contained unrecognisable mystery values. It was a miracle that the system actually ran at all, given the state it was in.

I did the only thing that one can do in such a situation. I rolled up my sleeves and set to work cleaning up the data.

It took me a month. One whole month.

I eventually managed to rip out the Pokémon exception handling, harden the system, and make it behave properly. That took even longer.

It’s now more than five years since I last worked on BKB. When I handed it over, it worked properly, it was robust, and the data had long since been licked into shape. I don’t know what development has been done on it since then, but it was still faithfully doing its job when I left the place earlier this year. So if you ever feel inclined to question what I have to say about exceptions, just head over to https://services.parliament.uk/bills/. Getting that little corner of the web to the place where it is today left me with some scar tissue. And it’s that scar tissue that makes me twitch whenever I see bad error handling code.

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