Adding examples and documentation for caching (#5514)

Author: pratyushmittal

docs/api-guide/caching.md

@@ -0,0 +1,54 @@
+# Caching
+
+> A certain woman had a very sharp conciousness but almost no 
+> memory ... She remembered enough to work, and she worked hard.
+> - Lydia Davis
+
+Caching in REST Framework works well with the cache utilities
+provided in Django.
+
+---
+
+## Using cache with apiview and viewsets
+
+Django provides a [`method_decorator`][decorator] to use
+decorators with class based views. This can be used with
+with other cache decorators such as [`cache_page`][page] and
+[`vary_on_cookie`][cookie].
+
+```python
+from rest_framework.response import Response
+from rest_framework.views import APIView
+from rest_framework import viewsets
+
+class UserViewSet(viewsets.Viewset):
+    
+    # Cache requested url for each user for 2 hours
+    @method_decorator(cache_page(60*60*2))  
+    @method_decorator(vary_on_cookie)
+    def list(self, request, format=None):
+        content = {
+            'user_feed': request.user.get_user_feed()
+        }
+        return Response(content)
+
+class PostView(APIView):
+
+    # Cache page for the requested url
+    @method_decorator(cache_page(60*60*2))  
+    def get(self, request, format=None):
+        content = {
+            'title': 'Post title',
+            'body': 'Post content'
+        }
+        return Response(content)
+```
+
+**NOTE:** The [`cache_page`][page] decorator only caches the
+`GET` and `HEAD` responses with status 200.
+
+
+[django]: https://docs.djangoproject.com/en/dev/topics/cache/
+[page]: https://docs.djangoproject.com/en/dev/topics/cache/#the-per-view-cache
+[cookie]: https://docs.djangoproject.com/en/dev/topics/http/decorators/#django.views.decorators.vary.vary_on_cookie
+[decorator]: https://docs.djangoproject.com/en/dev/topics/class-based-views/intro/#decorating-the-class