gergelypolonkai-web-jekyll/_posts/2015-06-07-paramconverter-a-la-django.markdown

layout	title	date	tags	published	author
post	@ParamConverter à la Django	2015-06-07 20:14:32+02:00	python django	true	name email Gergely Polonkai gergely@polonkai.eu

One thing I really miss from Django is Symfony’s @ParamConverter. It made my life so much easier while developing with Symfony. In Django, of course, there is get_object_or_404, but, for example, in one of my projects I had a view that had to resolve 6(!) objects from the URL, and writing get_object_or_404 six times is not what a programmer likes to do (yes, this view had a refactor later on). A quick Google search gave me one usable result (in French), but it was very generalized that I cannot always use. Also, it was using a middleware, which may introduce performance issues sometimes^{[citation needed]}. So I decided to go with decorators, and at the end, I came up with this:

{% gist gergelypolonkai/498a32297f39b4960ad7 helper.py %}

Now I can decorate my views, either class or function based, with @convert_params(User, (Article, 'aid'), (Paragraph, None, 'pid'), (AnotherObject, None, None, 'obj')) and all the magic happens in the background. The user_id parameter passed to my function will be popped off, and be resolved against the User model by using the id field; the result is put in the new user parameter. For Article, the aid parameter will be matched against the id field of the Article model putting the result into article, and finally, the another_object_id will be matched against the id field of the AnotherObject model, but in this case, the result is passed to the original function as obj.