Add new sane_rowcount_w_returning flag

Added a new class of "rowcount support" for dialects that is specific to
when "RETURNING", which on SQL Server looks like "OUTPUT inserted", is in
use, as the PyODBC backend isn't able to give us rowcount on an UPDATE or
DELETE statement when OUTPUT is in effect.  This primarily affects the ORM
when a flush is updating a row that contains server-calcluated values,
raising an error if the backend does not return the expected row count.
PyODBC now states that it supports rowcount except if OUTPUT.inserted is
present, which is taken into account by the ORM during a flush as to
whether it will look for a rowcount.

ORM tests are implicit in existing tests run against PyODBC

Fixes: #4062
Change-Id: Iff17cbe4c7a5742971ed85a4d58660c18cc569c2

1 files changed, 23 insertions, 0 deletions

diff --git a/lib/sqlalchemy/testing/requirements.py b/lib/sqlalchemy/testing/requirements.py
index 08a7b1ced..327362bf6 100644
--- a/lib/sqlalchemy/testing/requirements.py
+++ b/lib/sqlalchemy/testing/requirements.py
@@ -193,6 +193,29 @@ class SuiteRequirements(Requirements):
 
         return exclusions.open()
 
+
+    @property
+    def sane_rowcount(self):
+        return exclusions.skip_if(
+            lambda config: not config.db.dialect.supports_sane_rowcount,
+            "driver doesn't support 'sane' rowcount"
+        )
+
+    @property
+    def sane_multi_rowcount(self):
+        return exclusions.fails_if(
+            lambda config: not config.db.dialect.supports_sane_multi_rowcount,
+            "driver %(driver)s %(doesnt_support)s 'sane' multi row count"
+        )
+
+    @property
+    def sane_rowcount_w_returning(self):
+        return exclusions.fails_if(
+            lambda config:
+                not config.db.dialect.supports_sane_rowcount_returning,
+            "driver doesn't support 'sane' rowcount when returning is on"
+        )
+
     @property
     def empty_inserts(self):
         """target platform supports INSERT with no values, i.e.