Monday, September 8, 2008

Code Generation templates act as your Documentation

[This was originally posted at]

On every project, there's an endless list of things you're "supposed" to do, like documentation. I've personally never met a developer who enjoys this, so it usually gets shuffled to the side. One way to simplify documentation is to code generate what you can, because then the code generation template becomes your documentation.

Here's an example: I once was on a project where we had a large amount of base SQL data - things like populating dropdowns, security info, and config settings. Initially this was all done with hard-coded SQL files using tons of insert and update statements. Of course, to explain how to write all those inserts and updates, which tables they should alter, and what values they should set, there was tons of tedious MS word docs. Developers would constantly write failing SQL scripts, then recheck the documentation, fix their scripts, and keep trying until it worked. People always had questions like "Should the 'CodeId' column be set to the primary key from the 'RoleLookup' table? Technically, it "worked", it was just slow, brittle, and costing the business money.

Then, we tried migrating all those scripts over to xml files that got actively code generated into SQL scripts. All of a sudden, in order to actually write those templates, we needed to understand what the rules were. What tables, columns, and rows should be affected? What does an attribute like "active=true" translate into for a SQL script? So, this forced us to flush out all the rules. As time went on, when developers had questions, they could see all the rules "documented" in the code of the generation template (the *.cst file in CodeSmith). People essentially would say: "What happens if I set the entityScope attribute to zero? Oh, the code generator template specifically checks for that and will create this special insert in TableX when that happens. Ah, I see..."

Of course there are many other benefits of code generation, but I think this is an often overlooked one: generating the code from an xml file forces you to understand what you're actually doing. If you need to "explain" how to write code to a code generator, then anyone else can look at that explanation too. This is a similar principle to writing self-documenting code.

This also hit home after I wrote a UI page code generator that was 3000 lines long. I realized that in order for  a developer to create a UI page for that project, they essentially needed to (manually) reproduce whatever that template was doing, which meant that they had to understand 3000 lines of trivia. Anyone with questions on producing basic UI pages could always "look up" how the code generator did it.

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