Fixed #9307 -- Added the ability to pickle the Query class used by the Oracle

backend.

This allows Querysets to be cached for Oracle and should provide a model for
adding pickling support to other (external) database backends that need a
custom Query class.

Thanks to Justin Bronn for some assistance with this patch.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@9272 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/backends/oracle/query.py

@@ -25,6 +25,18 @@ def query_class(QueryClass, Database):
         pass
 
     class OracleQuery(QueryClass):
+        def __reduce__(self):
+            """
+            Enable pickling for this class (normal pickling handling doesn't
+            work as Python can only pickle module-level classes by default).
+            """
+            if hasattr(QueryClass, '__getstate__'):
+                assert hasattr(QueryClass, '__setstate__')
+                data = self.__getstate__()
+            else:
+                data = self.__dict__
+            return (unpickle_query_class, (QueryClass,), data)
+
         def resolve_columns(self, row, fields=()):
             # If this query has limit/offset information, then we expect the
             # first column to be an extra "_RN" column that we need to throw
@@ -120,3 +132,17 @@ def query_class(QueryClass, Database):
 
     _classes[QueryClass] = OracleQuery
     return OracleQuery
+
+def unpickle_query_class(QueryClass):
+    """
+    Utility function, called by Python's unpickling machinery, that handles
+    unpickling of Oracle Query subclasses.
+    """
+    # XXX: Would be nice to not have any dependency on cx_Oracle here. Since
+    # modules can't be pickled, we need a way to know to load the right module.
+    import cx_Oracle
+
+    klass = query_class(QueryClass, cx_Oracle)
+    return klass.__new__(klass)
+unpickle_query_class.__safe_for_unpickling__ = True
+

django/db/models/sql/query.py

@@ -27,9 +27,9 @@ try:
 except NameError:
     from sets import Set as set     # Python 2.3 fallback
 
-__all__ = ['Query']
+__all__ = ['Query', 'BaseQuery']
 
-class Query(object):
+class BaseQuery(object):
     """
     A single SQL query.
     """
@@ -1757,7 +1757,9 @@ class Query(object):
 # Use the backend's custom Query class if it defines one. Otherwise, use the
 # default.
 if connection.features.uses_custom_query_class:
-    Query = connection.ops.query_class(Query)
+    Query = connection.ops.query_class(BaseQuery)
+else:
+    Query = BaseQuery
 
 def get_order_dir(field, default='ASC'):
     """