From a97f690e5dbfe9c8d1034a94373da0bedd681814 Mon Sep 17 00:00:00 2001
From: Malcolm Tredinnick <malcolm.tredinnick@gmail.com>
Date: Mon, 28 Apr 2008 14:14:41 +0000
Subject: [PATCH] Added the ability to pickle and unpickle QuerySets and Query
 classes.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@7499 bcc190cf-cafb-0310-a4f2-bffc1f526a37
---
 django/db/models/query.py     | 13 ++++++++++++-
 django/db/models/sql/query.py | 18 ++++++++++++++++++
 docs/db-api.txt               | 23 +++++++++++++++++++++++
 3 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/django/db/models/query.py b/django/db/models/query.py
index 3011b9d9a6..65048c7ba8 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -28,6 +28,17 @@ class QuerySet(object):
     # PYTHON MAGIC METHODS #
     ########################
 
+    def __getstate__(self):
+        """
+        Allows the Queryset to be pickled.
+        """
+        # Force the cache to be fully populated.
+        len(self)
+
+        obj_dict = self.__dict__.copy()
+        obj_dict['_iter'] = None
+        return obj_dict
+
     def __repr__(self):
         return repr(list(self))
 
@@ -37,7 +48,7 @@ class QuerySet(object):
         # whilst not messing up any existing iterators against the queryset.
         if self._result_cache is None:
             if self._iter:
-                self._result_cache = list(self._iter())
+                self._result_cache = list(self._iter)
             else:
                 self._result_cache = list(self.iterator())
         elif self._iter:
diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index bfed984953..7e9fb00418 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -99,6 +99,24 @@ class Query(object):
         memo[id(self)] = result
         return result
 
+    def __getstate__(self):
+        """
+        Pickling support.
+        """
+        obj_dict = self.__dict__.copy()
+        del obj_dict['connection']
+        return obj_dict
+
+    def __setstate__(self, obj_dict):
+        """
+        Unpickling support.
+        """
+        self.__dict__.update(obj_dict)
+        # XXX: Need a better solution for this when multi-db stuff is
+        # supported. It's the only class-reference to the module-level
+        # connection variable.
+        self.connection = connection
+
     def get_meta(self):
         """
         Returns the Options instance (the model._meta) from which to start
diff --git a/docs/db-api.txt b/docs/db-api.txt
index 6299f3497d..405ed87cef 100644
--- a/docs/db-api.txt
+++ b/docs/db-api.txt
@@ -376,6 +376,29 @@ You can evaluate a ``QuerySet`` in the following ways:
       iterating over a ``QuerySet`` will take advantage of your database to
       load data and instantiate objects only as you need them.
 
+
+Pickling QuerySets
+~~~~~~~~~~~~~~~~~~
+
+If you pickle_ a ``QuerySet``, this will also force all the results to be
+loaded into memory prior to pickling. This is because pickling is usually used
+as a precursor to caching and when the cached queryset is reloaded, you want
+the results to already be present. This means that when you unpickle a
+``QuerySet``, it contains the results at the moment it was pickled, rather
+than the results that are currently in the database.
+
+If you only want to pickle the necessary information to recreate the
+``Queryset`` from the database at a later time, pickle the ``query`` attribute
+of the ``QuerySet``. You can then recreate the original ``QuerySet`` (without
+any results loaded) using some code like this::
+
+    >>> import pickle
+    >>> query = pickle.loads(s)     # Assuming 's' is the pickled string.
+    >>> qs = MyModel.objects.all()
+    >>> qs.query = query            # Restore the original 'query'.
+
+.. _pickle: http://docs.python.org/lib/module-pickle.html
+
 Limiting QuerySets
 ------------------