Respects ResultProxy.supports_sane_rowcount()

The check for matched rowcount when the alembic_version table is updated or
deleted from is now conditional based on whether or not the dialect
supports the concept of "rowcount" for UPDATE or DELETE rows matched.  Some
third party dialects do not support this concept.  Pull request courtesy Ke
Zhu.

Closes: #667
Pull-request: #667
Pull-request-sha: a0d45ed

Change-Id: I09c9b540d8e21a94728085270eb20ba2273cbdb1

alembic/runtime/migration.py

@@ -676,7 +676,11 @@ def _delete_version(self, version):
                 == literal_column("'%s'" % version)
             )
         )
-        if not self.context.as_sql and ret.rowcount != 1:
+        if (
+            not self.context.as_sql
+            and self.context.dialect.supports_sane_rowcount
+            and ret.rowcount != 1
+        ):
             raise util.CommandError(
                 "Online migration expected to match one "
                 "row when deleting '%s' in '%s'; "
@@ -697,7 +701,11 @@ def _update_version(self, from_, to_):
                 == literal_column("'%s'" % from_)
             )
         )
-        if not self.context.as_sql and ret.rowcount != 1:
+        if (
+            not self.context.as_sql
+            and self.context.dialect.supports_sane_rowcount
+            and ret.rowcount != 1
+        ):
             raise util.CommandError(
                 "Online migration expected to match one "
                 "row when updating '%s' to '%s' in '%s'; "

docs/build/unreleased/rowcount.rst

@@ -0,0 +1,8 @@
+.. change::
+    :tags: bug, environment
+
+    The check for matched rowcount when the alembic_version table is updated or
+    deleted from is now conditional based on whether or not the dialect
+    supports the concept of "rowcount" for UPDATE or DELETE rows matched.  Some
+    third party dialects do not support this concept.  Pull request courtesy Ke
+    Zhu.

tests/test_version_table.py

@@ -262,6 +262,14 @@ def test_update_no_match(self):
             _up("x", "b"),
         )
 
+    def test_update_no_match_no_sane_rowcount(self):
+        self.updater.update_to_step(_up(None, "a", True))
+        self.updater.heads.add("x")
+        with mock.patch.object(
+            self.connection.dialect, "supports_sane_rowcount", False
+        ):
+            self.updater.update_to_step(_up("x", "b"))
+
     def test_update_multi_match(self):
         self.connection.execute(version_table.insert(), version_num="a")
         self.connection.execute(version_table.insert(), version_num="a")
@@ -275,6 +283,16 @@ def test_update_multi_match(self):
             _up("a", "b"),
         )
 
+    def test_update_multi_match_no_sane_rowcount(self):
+        self.connection.execute(version_table.insert(), version_num="a")
+        self.connection.execute(version_table.insert(), version_num="a")
+
+        self.updater.heads.add("a")
+        with mock.patch.object(
+            self.connection.dialect, "supports_sane_rowcount", False
+        ):
+            self.updater.update_to_step(_up("a", "b"))
+
     def test_delete_no_match(self):
         self.updater.update_to_step(_up(None, "a", True))
 
@@ -287,6 +305,15 @@ def test_delete_no_match(self):
             _down("x", None, True),
         )
 
+    def test_delete_no_matchno_sane_rowcount(self):
+        self.updater.update_to_step(_up(None, "a", True))
+
+        self.updater.heads.add("x")
+        with mock.patch.object(
+            self.connection.dialect, "supports_sane_rowcount", False
+        ):
+            self.updater.update_to_step(_down("x", None, True))
+
     def test_delete_multi_match(self):
         self.connection.execute(version_table.insert(), version_num="a")
         self.connection.execute(version_table.insert(), version_num="a")
@@ -299,3 +326,13 @@ def test_delete_multi_match(self):
             self.updater.update_to_step,
             _down("a", None, True),
         )
+
+    def test_delete_multi_match_no_sane_rowcount(self):
+        self.connection.execute(version_table.insert(), version_num="a")
+        self.connection.execute(version_table.insert(), version_num="a")
+
+        self.updater.heads.add("a")
+        with mock.patch.object(
+            self.connection.dialect, "supports_sane_rowcount", False
+        ):
+            self.updater.update_to_step(_down("a", None, True))