Fixed #17168 - Noted TransactionMiddleware only works with "default" database alias.

Thanks codeinthehole for the draft patch.

docs/topics/db/transactions.txt

@@ -56,6 +56,13 @@ database cursor (which is mapped to its own database connection internally).
 
 .. _transaction-management-functions:
 
+.. note::
+
+    The ``TransactionMiddleware`` only affects the database aliased
+    as "default" within your :setting:`DATABASES` setting.  If you are using
+    multiple databases and want transaction control over databases other than
+    "default", you will need to write your own transaction middleware.
+
 Controlling transaction management in views
 ===========================================