Add Django @ParamConverter post

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

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+---
+layout:    post
+title:     "@ParamConverter à la Django"
+date:      2015-06-07 20:14:32+02:00
+tags:      [python, django]
+published: true
+author:
+    name:  Gergely Polonkai
+    email: gergely@polonkai.eu
+---
+One thing I really miss from [Django](https://www.djangoproject.com/)
+is [Symfony](http://symfony.com)’s
+[@ParamConverter](http://symfony.com/doc/current/bundles/SensioFrameworkExtraBundle/annotations/converters.html). It
+made my life so much easier while developing with Symfony. In Django,
+of course, there is
+[get_object_or_404](https://docs.djangoproject.com/en/dev/topics/http/shortcuts/#get-object-or-404),
+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. A quick Google search gave me one
+[usable result](http://openclassrooms.com/forum/sujet/middleware-django-genre-paramconverter-doctrine)
+(in French), but it was very generalized that I cannot always
+use. Also, it was using a middleware, which may introduce performance
+issues sometimes<sup>[citation needed]</sup>. 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`.