Add a monkey-patching util for sqlalchemy-migrate

Nova and other projects use sqlalchemy-migrate for DB schema
migrations. Unfortunately, this project looks like to be dead,
but have some important bugs which makes lives of OpenStack
developers harder (e. g. creation of a new unique constraint
in SQLite leads to deletion of all existing unique constraints).

Nova has some workarounds for bugs and limitations of sqlalchemy-migrate,
though it would be nice to have those directly in sqlalchemy-migrate
(at least in form of a monkey-patch for now). Oslo seems to be
a good place to store this monkey-patch, so Nova and other projects
could reuse it.

This patch:
  - makes it possible to use the unified drop_unique_constraint()
    function for SQLite backend
  - fixes a bug in sqlalchemy-migrate that leads to deletion of
    existing unique constraints of a table when a new one is added
    (SQLite backend)

Blueprint: oslo-sqlalchemy-migrate-uc-fixes

Change-Id: Ifac07abac3814b3ea4dea5840b17a711f4b24b8d

1 files changed, 95 insertions, 0 deletions

diff --git a/tests/unit/db/sqlalchemy/test_migrate.py b/tests/unit/db/sqlalchemy/test_migrate.py
new file mode 100644
index 0000000..6724b5c
--- /dev/null
+++ b/tests/unit/db/sqlalchemy/test_migrate.py
@@ -0,0 +1,95 @@
+# Copyright (c) 2013 OpenStack Foundation
+# All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+
+from migrate.changeset.constraint import UniqueConstraint
+from migrate.changeset.databases import sqlite
+import sqlalchemy as sa
+
+from openstack.common.db.sqlalchemy import migration
+from openstack.common.db.sqlalchemy import session
+from tests.unit.db.sqlalchemy import base as test_base
+
+
+def uniques(*constraints):
+    """Make a sequence of UniqueConstraint instances easily comparable
+
+        Convert a sequence of UniqueConstraint instances into a set of
+        tuples of form (constraint_name, (constraint_columns)) so that
+        assertEquals() will be able to compare sets of unique constraints
+
+    """
+
+    return set((uc.name, tuple(uc.columns.keys())) for uc in constraints)
+
+
+class TestSqliteUniqueConstraints(test_base.DbTestCase):
+    def setUp(self):
+        super(TestSqliteUniqueConstraints, self).setUp()
+
+        migration.patch_migrate()
+
+        self.helper = sqlite.SQLiteHelper()
+
+        sa.Table(
+            'test_table',
+            sa.schema.MetaData(bind=session.get_engine()),
+            sa.Column('a', sa.Integer),
+            sa.Column('b', sa.String(10)),
+            sa.Column('c', sa.Integer),
+            sa.UniqueConstraint('a', 'b', name='unique_a_b'),
+            sa.UniqueConstraint('b', 'c', name='unique_b_c')
+        ).create()
+
+        # NOTE(rpodolyaka): it's important to use the reflected table here
+        #                   rather than original one because this is what
+        #                   we actually do in db migrations code
+        self.reflected_table = sa.Table(
+            'test_table',
+            sa.schema.MetaData(bind=session.get_engine()),
+            autoload=True
+        )
+
+    def test_get_unique_constraints(self):
+        table = self.reflected_table
+
+        existing = uniques(*self.helper._get_unique_constraints(table))
+        should_be = uniques(
+            sa.UniqueConstraint(table.c.a, table.c.b, name='unique_a_b'),
+            sa.UniqueConstraint(table.c.b, table.c.c, name='unique_b_c'),
+        )
+        self.assertEquals(should_be, existing)
+
+    def test_add_unique_constraint(self):
+        table = self.reflected_table
+        UniqueConstraint(table.c.a, table.c.c, name='unique_a_c').create()
+
+        existing = uniques(*self.helper._get_unique_constraints(table))
+        should_be = uniques(
+            sa.UniqueConstraint(table.c.a, table.c.b, name='unique_a_b'),
+            sa.UniqueConstraint(table.c.b, table.c.c, name='unique_b_c'),
+            sa.UniqueConstraint(table.c.a, table.c.c, name='unique_a_c'),
+        )
+        self.assertEquals(should_be, existing)
+
+    def test_drop_unique_constraint(self):
+        table = self.reflected_table
+        UniqueConstraint(table.c.a, table.c.b, name='unique_a_b').drop()
+
+        existing = uniques(*self.helper._get_unique_constraints(table))
+        should_be = uniques(
+            sa.UniqueConstraint(table.c.b, table.c.c, name='unique_b_c'),
+        )
+        self.assertEquals(should_be, existing)