From 5ad4907a0df2d30cf17fa3515404ccdcb8398ef6 Mon Sep 17 00:00:00 2001
From: Jeppe Fihl-Pearson <jeppe@memrise.com>
Date: Thu, 25 Apr 2019 10:45:05 +0100
Subject: [PATCH] Add more context to warnings emitted from Django when
 unpickling objects

When upgrading Django, Django will emit a warning whenever an object is being
unpickled which was created with a different version of Django. This warning
isn't very easy to action as it doesn't contain any context about what object
it is or where it may have got the object from. The warning might look
something like this:

> WARNING [2019-04-25 09:41:48,525] warnings: /path/to/virtualenv/lib/python3.7/site-packages/django_redis/serializers/pickle.py:35: RuntimeWarning: Pickled model instance's Django version 2.1.8 does not match the current version 2.2.
>   return pickle.loads(value)

This change will loop through each warning emitted during the deserialization
of the cached item and append the cache key to the warning which at least would
give some context as to why that is happening, so the warning message instead
becomes:

> WARNING [2019-04-25 09:41:48,525] warnings: /path/to/virtualenv/lib/python3.7/site-packages/django_redis/serializers/pickle.py:35: RuntimeWarning: Pickled model instance's Django version 2.1.8 does not match the current version 2.2. (cache key: :1:user)
>   return pickle.loads(value)

given the cache key `user`.
---
 django_redis/client/default.py | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/django_redis/client/default.py b/django_redis/client/default.py
index 9fc2cb72..ea2e45e3 100644
--- a/django_redis/client/default.py
+++ b/django_redis/client/default.py
@@ -5,6 +5,7 @@
 import random
 import re
 import socket
+import warnings
 from collections import OrderedDict
 
 from django.conf import settings
@@ -208,7 +209,7 @@ def get(self, key, default=None, version=None, client=None):
         if value is None:
             return default
 
-        return self.decode(value)
+        return self.decode(value, key)
 
     def persist(self, key, version=None, client=None):
         if client is None:
@@ -304,9 +305,11 @@ def clear(self, client=None):
         except _main_exceptions as e:
             raise ConnectionInterrupted(connection=client, parent=e)
 
-    def decode(self, value):
+    def decode(self, value, key):
         """
         Decode the given value.
+
+        Key is used to provide better context to warnings.
         """
         try:
             value = int(value)
@@ -316,7 +319,18 @@ def decode(self, value):
             except CompressorError:
                 # Handle little values, chosen to be not compressed
                 pass
-            value = self._serializer.loads(value)
+
+            with warnings.catch_warnings(record=True) as caught_warnings:
+                value = self._serializer.loads(value)
+
+            for warning in caught_warnings:
+                warnings.warn_explicit(
+                    warning.category("{} (cache key: {})".format(str(warning.message), key)),
+                    warning.category,
+                    warning.filename,
+                    warning.lineno,
+                )
+
         return value
 
     def encode(self, value):
@@ -356,7 +370,7 @@ def get_many(self, keys, version=None, client=None):
         for key, value in zip(map_keys, results):
             if value is None:
                 continue
-            recovered_data[map_keys[key]] = self.decode(value)
+            recovered_data[map_keys[key]] = self.decode(value, key)
         return recovered_data
 
     def set_many(self, data, timeout=DEFAULT_TIMEOUT, version=None, client=None):