Gregor Müllegger committed ab05610

Added documentation for cast() queryset method.

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 .. note:: 
     This is inefficient for large querysets, as it results in n
-    queries to the subtype tables.  It would be possible to write a
-    QuerySet subclass that could reduce this to k queries, where there
-    are k subtypes in the inheritance tree.
+    queries to the subtype tables.  You can use the ``cast()`` method
+    on a queryset to reduce this to as many queries as subtypes are
+    involved.
+    nearby_places = Place.objects.filter(location='here')
+    for pace in nearby_places.cast():
+        # ...
+.. note:: 
+    The ``cast()`` method on a queryset does *not* return another
+    queryset but an already evaluated result of the database query.
+    This means that you cannot chain any athor queryset methods after
+    you have called ``cast()``.