Add autocommit_block

Added new feature :meth:`.MigrationContext.autocommit_block`, a special
directive which will provide for a non-transactional block inside of a
migration script. The feature requres that: the database driver
(e.g. DBAPI) supports the AUTOCOMMIT isolation mode.  The directive
also necessarily needs to COMMIT the existing transaction in progress
in order to enter autocommit mode.

Change-Id: I107fe9772595db189b6ebeba6535ac8f275b3fe5
Fixes: #123

3 files changed, 10 insertions, 0 deletions

diff --git a/alembic/testing/__init__.py b/alembic/testing/__init__.py
index ad0ae4c..4b66926 100644
--- a/alembic/testing/__init__.py
+++ b/alembic/testing/__init__.py
@@ -12,6 +12,8 @@ from .assertions import emits_python_deprecation_warning  # noqa
 from .assertions import eq_  # noqa
 from .assertions import eq_ignore_whitespace  # noqa
 from .assertions import is_  # noqa
+from .assertions import is_false  # noqa
 from .assertions import is_not_  # noqa
+from .assertions import is_true  # noqa
 from .assertions import ne_  # noqa
 from .fixtures import TestBase  # noqa
diff --git a/alembic/testing/assertions.py b/alembic/testing/assertions.py
index 750c526..3dc08f0 100644
--- a/alembic/testing/assertions.py
+++ b/alembic/testing/assertions.py
@@ -8,7 +8,9 @@ from sqlalchemy.testing.assertions import assert_raises  # noqa
 from sqlalchemy.testing.assertions import assert_raises_message  # noqa
 from sqlalchemy.testing.assertions import eq_  # noqa
 from sqlalchemy.testing.assertions import is_  # noqa
+from sqlalchemy.testing.assertions import is_false  # noqa
 from sqlalchemy.testing.assertions import is_not_  # noqa
+from sqlalchemy.testing.assertions import is_true  # noqa
 from sqlalchemy.testing.assertions import ne_  # noqa
 from sqlalchemy.util import decorator
 
diff --git a/alembic/testing/requirements.py b/alembic/testing/requirements.py
index c8d76b8..9038a45 100644
--- a/alembic/testing/requirements.py
+++ b/alembic/testing/requirements.py
@@ -16,6 +16,12 @@ class SuiteRequirements(Requirements):
         return exclusions.open()
 
     @property
+    def autocommit_isolation(self):
+        """target database should support 'AUTOCOMMIT' isolation level"""
+
+        return exclusions.closed()
+
+    @property
     def unique_constraint_reflection(self):
         def doesnt_have_check_uq_constraints(config):
             from sqlalchemy import inspect