Fixed transaction handling for a number of operations on related objects.

Thanks Anssi and Aymeric for the reviews. Refs #21174.

1 files changed, 13 insertions, 1 deletions

diff --git a/docs/releases/1.8.txt b/docs/releases/1.8.txt
index 1f56c3109e..789c1db535 100644
--- a/docs/releases/1.8.txt
+++ b/docs/releases/1.8.txt
@@ -168,7 +168,19 @@ Backwards incompatible changes in 1.8
     deprecation timeline for a given feature, its removal may appear as a
     backwards incompatible change.
 
-...
+* Some operations on related objects such as
+  :meth:`~django.db.models.fields.related.RelatedManager.add()` or
+  :ref:`direct assignment<direct-assignment>` ran multiple data modifying
+  queries without wrapping them in transactions. To reduce the risk of data
+  corruption, all data modifying methods that affect multiple related objects
+  (i.e. ``add()``, ``remove()``, ``clear()``, and
+  :ref:`direct assignment<direct-assignment>`) now perform their data modifying
+  queries from within a transaction, provided your database supports
+  transactions.
+
+  This has one backwards incompatible side effect, signal handlers triggered
+  from these methods are now executed within the method's transaction and
+  any exception in a signal handler will prevent the whole operation.
 
 Miscellaneous
 ~~~~~~~~~~~~~