Fixed #14315 -- Made memcached backend handle negative incr/decr values

Thanks Michael Manfre for the report and initial patch and
Tobias McNulty for the review.

1 files changed, 6 insertions, 0 deletions

diff --git a/django/core/cache/backends/memcached.py b/django/core/cache/backends/memcached.py
index 9bb47c8344..2c3f198847 100644
--- a/django/core/cache/backends/memcached.py
+++ b/django/core/cache/backends/memcached.py
@@ -90,6 +90,9 @@ class BaseMemcachedCache(BaseCache):
 
     def incr(self, key, delta=1, version=None):
         key = self.make_key(key, version=version)
+        # memcached doesn't support a negative delta
+        if delta < 0:
+            return self._cache.decr(key, -delta)
         try:
             val = self._cache.incr(key, delta)
 
@@ -105,6 +108,9 @@ class BaseMemcachedCache(BaseCache):
 
     def decr(self, key, delta=1, version=None):
         key = self.make_key(key, version=version)
+        # memcached doesn't support a negative delta
+        if delta < 0:
+            return self._cache.incr(key, -delta)
         try:
             val = self._cache.decr(key, delta)