Assume relative revisions belong to alembic

migration_cli alembic plugin returned that it doesn't know anything
about relative revisions. This cause the situation when one could not
perform relative upgrades or downgrades.

Change-Id: I3c0eddf75d4a8c91c7a23c6fbad947900ec0ac94
Closes-Bug: 1486790

oslo_db/sqlalchemy/migration_cli/ext_alembic.py

@@ -94,6 +94,15 @@ def stamp(self, revision):
     def has_revision(self, rev_id):
         if rev_id in ['base', 'head']:
             return True
+
+        # Although alembic supports relative upgrades and downgrades,
+        # get_revision always returns False for relative revisions.
+        # Since only alembic supports relative revisions, assume the
+        # revision belongs to this plugin.
+        if rev_id:  # rev_id can be None, so the check is required
+            if '-' in rev_id or '+' in rev_id:
+                return True
+
         script = alembic_script.ScriptDirectory(
             self.config.get_main_option('alembic_repo_path'))
         try:

oslo_db/tests/sqlalchemy/test_migrate_cli.py

@@ -107,6 +107,8 @@ def test_has_revision(self, command):
                 'test')
             self.assertIs(True, self.alembic.has_revision(None))
             self.assertIs(True, self.alembic.has_revision('head'))
+            # relative revision, should be True for alembic
+            self.assertIs(True, self.alembic.has_revision('+1'))
 
     def test_has_revision_negative(self, command):
         with mock.patch(('oslo_db.sqlalchemy.migration_cli.'
@@ -198,6 +200,8 @@ def test_has_revision_negative(self, command):
             mocked.Collection().version.side_effect = ValueError
             self.assertIs(False, self.migrate.has_revision('test'))
             mocked.Collection().version.assert_called_once_with('test')
+            # relative revision, should be False for migrate
+            self.assertIs(False, self.migrate.has_revision('+1'))
 
 
 class TestMigrationManager(test_base.BaseTestCase):