2015-06-07 18:16:45 +00:00
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---
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layout: post
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title: "@ParamConverter à la Django"
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2016-02-26 15:19:42 +00:00
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date: 2015-06-07T18:14:32Z
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2015-06-07 18:16:45 +00:00
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tags: [python, django]
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published: true
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author:
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name: Gergely Polonkai
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email: gergely@polonkai.eu
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---
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One thing I really miss from [Django](https://www.djangoproject.com/)
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is [Symfony](http://symfony.com)’s
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[@ParamConverter](http://symfony.com/doc/current/bundles/SensioFrameworkExtraBundle/annotations/converters.html). It
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made my life so much easier while developing with Symfony. In Django,
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of course, there is
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[get_object_or_404](https://docs.djangoproject.com/en/dev/topics/http/shortcuts/#get-object-or-404),
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2015-06-22 20:42:32 +00:00
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but, for example, in one of my projects I had a view that had to resolve 6(!)
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objects from the URL, and writing `get_object_or_404` six times is not what a
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programmer likes to do (yes, this view had a refactor later on). A quick Google
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search gave me one [usable
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result](http://openclassrooms.com/forum/sujet/middleware-django-genre-paramconverter-doctrine)
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(in French), but it was very generalized that I cannot always use. Also, it was
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using a middleware, which may introduce performance issues
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sometimes<sup>[citation needed]</sup>. So I decided to go with decorators, and
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at the end, I came up with this:
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2015-06-07 18:16:45 +00:00
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{% gist gergelypolonkai/498a32297f39b4960ad7 helper.py %}
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Now I can decorate my views, either class or function based, with
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`@convert_params(User, (Article, 'aid'), (Paragraph, None, 'pid'),
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(AnotherObject, None, None, 'obj'))` and all the magic happens in the
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background. The `user_id` parameter passed to my function will be
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popped off, and be resolved against the `User` model by using the `id`
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field; the result is put in the new `user` parameter. For Article, the
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`aid` parameter will be matched against the `id` field of the
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`Article` model putting the result into `article`, and finally, the
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`another_object_id` will be matched against the `id` field of the
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`AnotherObject` model, but in this case, the result is passed to the
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original function as `obj`.
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