SoftDeleteMixin: coerce deleted param to be an integer

PostgreSQL is very strict about types and won't perform an automatic
type cast when trying to pass e.g. a boolean `false` value to be
INSERT'ed or UPDATE'ed.

Coerce the value of deleted bound parameter to always be an integer
in the DB layer by adding a custom SQLAlchemy integer type decorator
to make PostgreSQL happy, should someone pass a boolean value for
deleted column (it was meant to be of boolean type, but is integer
instead to allow for Nova use case of shadow tables and compound
unique constraints on something + deleted).

Closes-Bug: #1644513

Change-Id: I13c6233cfeb611b1b106eedfc9b57d2af313c46b

oslo_db/sqlalchemy/models.py

@@ -23,10 +23,12 @@ SQLAlchemy models.
 import six
 
 from oslo_utils import timeutils
-from sqlalchemy import Column, Integer
+from sqlalchemy import Column
 from sqlalchemy import DateTime
 from sqlalchemy.orm import object_mapper
 
+from oslo_db.sqlalchemy import types
+
 
 class ModelBase(six.Iterator):
     """Base class for models."""
@@ -139,7 +141,7 @@ class TimestampMixin(object):
 
 class SoftDeleteMixin(object):
     deleted_at = Column(DateTime)
-    deleted = Column(Integer, default=0)
+    deleted = Column(types.SoftDeleteInteger, default=0)
 
     def soft_delete(self, session):
         """Mark this object as deleted."""

oslo_db/sqlalchemy/types.py

@@ -12,7 +12,7 @@
 
 import json
 
-from sqlalchemy.types import TypeDecorator, Text
+from sqlalchemy.types import Integer, TypeDecorator, Text
 from sqlalchemy.dialects import mysql
 
 
@@ -73,3 +73,20 @@ class JsonEncodedList(JsonEncodedType):
     http://docs.sqlalchemy.org/en/rel_1_0/orm/extensions/mutable.html
     """
     type = list
+
+
+class SoftDeleteInteger(TypeDecorator):
+    """Coerce a bound param to be a proper integer before passing it to DBAPI.
+
+    Some backends like PostgreSQL are very strict about types and do not
+    perform automatic type casts, e.g. when trying to INSERT a boolean value
+    like ``false`` into an integer column. Coercing of the bound param in DB
+    layer by the means of a custom SQLAlchemy type decorator makes sure we
+    always pass a proper integer value to a DBAPI implementation.
+
+    """
+
+    impl = Integer
+
+    def process_bind_param(self, value, dialect):
+        return int(value)

oslo_db/tests/sqlalchemy/test_models.py

@@ -14,10 +14,13 @@
 #    under the License.
 
 import collections
+import datetime
 
+import mock
 from oslotest import base as oslo_test
 from sqlalchemy import Column
 from sqlalchemy import Integer, String
+from sqlalchemy import event
 from sqlalchemy.ext.declarative import declarative_base
 
 from oslo_db.sqlalchemy import models
@@ -179,3 +182,50 @@ class TimestampMixinTest(oslo_test.BaseTestCase):
         for method in methods:
             self.assertTrue(hasattr(models.TimestampMixin, method),
                             "Method %s() is not found" % method)
+
+
+class SoftDeletedModel(BASE, models.ModelBase, models.SoftDeleteMixin):
+    __tablename__ = 'test_model_soft_deletes'
+
+    id = Column('id', Integer, primary_key=True)
+    smth = Column('smth', String(255))
+
+
+class SoftDeleteMixinTest(test_base.DbTestCase):
+    def setUp(self):
+        super(SoftDeleteMixinTest, self).setUp()
+
+        t = BASE.metadata.tables['test_model_soft_deletes']
+        t.create(self.engine)
+        self.addCleanup(t.drop, self.engine)
+
+        self.session = self.sessionmaker(autocommit=False)
+        self.addCleanup(self.session.close)
+
+    @mock.patch('oslo_utils.timeutils.utcnow')
+    def test_soft_delete(self, mock_utcnow):
+        dt = datetime.datetime.utcnow().replace(microsecond=0)
+        mock_utcnow.return_value = dt
+
+        m = SoftDeletedModel(id=123456, smth='test')
+        self.session.add(m)
+        self.session.commit()
+        self.assertEqual(0, m.deleted)
+        self.assertIs(None, m.deleted_at)
+
+        m.soft_delete(self.session)
+        self.assertEqual(123456, m.deleted)
+        self.assertIs(dt, m.deleted_at)
+
+    def test_soft_delete_coerce_deleted_to_integer(self):
+        def listener(conn, cur, stmt, params, context, executemany):
+            if 'insert' in stmt.lower():  # ignore SELECT 1 and BEGIN
+                self.assertNotIn('False', str(params))
+
+        event.listen(self.engine, 'before_cursor_execute', listener)
+        self.addCleanup(event.remove,
+                        self.engine, 'before_cursor_execute', listener)
+
+        m = SoftDeletedModel(id=1, smth='test', deleted=False)
+        self.session.add(m)
+        self.session.commit()