Django Rest API code generation with cog

After a good break for the holidays, a couple of weeks in the frozen wastes of Canada complete with arriving home with a stinking cold I am now at the, "this code won't write itself" part of the 80 days project.

There is quite a bit to do, but I am still finding distractions to spend time on.

I have been using django rest framework to create a REST api for the project.

Creating serializers, api classes and url specs for these frameworks is largely a matter of generating standard boiler plate code. This is the sort of stuff I hate doing: tedious and error prone.

I originally wrote my own noddy code generator to help with some of this, but was less than satisfied with the result: it was fine for my immediate needs, but as I add more models to the application I would need to do more autogeneration. I had the inescapable feeling that my code generator was probably more trouble than it was worth. At the same time, writing code like this by hand is deeply unsatisfying.

So, just when it was looking like I would have to start learning angular.js and build the front end, Ned Batchelder came to the rescue on Twitter by posting a link to a new release of cog.

Ned described it as "a small tool that does a small job well".

Sure enough, it does. It lets you embed python code (disguised as comments) within your code to do the code generation.

There are a few features in cog that appealed to me:

• the code generator can be run in a way that over-writes the input file with the newly generated code
• it calculates checksums for the generated code and embeds them in the output. This is useful as it allows it to spot if you have edited the code since it was generated and hence refuse to re-generate that code.
• you can re-run and it will update the existing code, assuming the checksums have not changed.

Armed with cog, I came up with codegen.py to generate the boring bits of api.py as well as urls.py and serializers.py.

I am quite happy with the results. Doug Hellmann had suggested maybe cookiecutter might be a better solution to this problem. In my case, I am using cookiecutter to get the base files for my django application, but this code generation cannot take place until you add some models, hence the need for cog.

Better still would be to combine the two and add codegen.py and suitable urls.py, serializers.py and api.py to the cookiecutter template. I'll add that to the list of things to do, if only to delay the learning of angular.js ;)