I created a short note on how to do this with the Forcier et photo gallery application tutorial. and other book. I am Django noob, so please take this material as not authoritative, and maybe not quite good. Here is a link to the message:
http://riceball.com/d/content/how-add-rest-api-existing-django-project
Basically, you create a new application and then write code for only three files: serializers.py, views.py and urls.py. You do not write anything in models.py. Instead, you import models from an existing application.
Then you start by creating serializers for all the models you want to expose, and then browsing for these serializers and finally the URLs to call these views.
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