Add initialization in StringMatchingFilterObj class

In order to support LIKE statement filter in OVO objects,
StringMatchingFilterObj class is introduced. However, this class
does not provide initial attributes of "starts", "contains" and
"ends".

In real usage, if these attributes are not initialized, we will
hit failures in method apply_filters() in db/_model_query.py.

This patch adds the initialization back.

Secondly, a typo of "obj_utils.StringMatchingContains" is revised
in this patch too.

Change-Id: If828068d8d08ff09dff6c63d53320bc397d32448
Closes-Bug: #1724446

doc/source/contributor/internals/objects_usage.rst

@@ -73,7 +73,7 @@ using example of DNSNameServer:
 
     # for fetching objects with substrings in a string field:
     from neutron.objects import utils as obj_utils
-    dnses = DNSNameServer.get_objects(context, address=obj_utils.StringMatchingContains('10.0.0'))
+    dnses = DNSNameServer.get_objects(context, address=obj_utils.StringContains('10.0.0'))
     # will return list of all dns name servers from DB that has '10.0.0' in their addresses
 
     # to update fields:

neutron/objects/utils.py

@@ -26,18 +26,17 @@ def convert_filters(**kwargs):
 
 
 class StringMatchingFilterObj(object):
-
     @property
     def is_contains(self):
-        return bool(getattr(self, "contains"))
+        return bool(getattr(self, "contains", False))
 
     @property
     def is_starts(self):
-        return bool(getattr(self, "starts"))
+        return bool(getattr(self, "starts", False))
 
     @property
     def is_ends(self):
-        return bool(getattr(self, "ends"))
+        return bool(getattr(self, "ends", False))
 
 
 class StringContains(StringMatchingFilterObj):

neutron/tests/unit/objects/db/test_api.py

@@ -20,6 +20,7 @@ from neutron.db import _model_query as model_query
 from neutron.db import models_v2
 from neutron.objects import base
 from neutron.objects.db import api
+from neutron.objects import utils as obj_utils
 from neutron.tests import base as test_base
 from neutron.tests.unit import testlib_api
 
@@ -98,6 +99,42 @@ class CRUDScenarioTestCase(testlib_api.SqlTestCase):
             self.ctxt, self.model, name='foo', status=None)
         self.assertEqual(obj, new_objs[0])
 
+    def test_get_objects_with_string_matching_filters_contains(self):
+        obj1 = api.create_object(self.ctxt, self.model, {'name': 'obj_con_1'})
+        obj2 = api.create_object(self.ctxt, self.model, {'name': 'obj_con_2'})
+        obj3 = api.create_object(self.ctxt, self.model, {'name': 'obj_3'})
+
+        objs = api.get_objects(
+            self.ctxt, self.model, name=obj_utils.StringContains('con'))
+        self.assertEqual(2, len(objs))
+        self.assertIn(obj1, objs)
+        self.assertIn(obj2, objs)
+        self.assertNotIn(obj3, objs)
+
+    def test_get_objects_with_string_matching_filters_starts(self):
+        obj1 = api.create_object(self.ctxt, self.model, {'name': 'pre_obj1'})
+        obj2 = api.create_object(self.ctxt, self.model, {'name': 'pre_obj2'})
+        obj3 = api.create_object(self.ctxt, self.model, {'name': 'obj_3'})
+
+        objs = api.get_objects(
+            self.ctxt, self.model, name=obj_utils.StringStarts('pre'))
+        self.assertEqual(2, len(objs))
+        self.assertIn(obj1, objs)
+        self.assertIn(obj2, objs)
+        self.assertNotIn(obj3, objs)
+
+    def test_get_objects_with_string_matching_filters_ends(self):
+        obj1 = api.create_object(self.ctxt, self.model, {'name': 'obj1_end'})
+        obj2 = api.create_object(self.ctxt, self.model, {'name': 'obj2_end'})
+        obj3 = api.create_object(self.ctxt, self.model, {'name': 'obj_3'})
+
+        objs = api.get_objects(
+            self.ctxt, self.model, name=obj_utils.StringEnds('end'))
+        self.assertEqual(2, len(objs))
+        self.assertIn(obj1, objs)
+        self.assertIn(obj2, objs)
+        self.assertNotIn(obj3, objs)
+
     def test_get_object_create_update_delete(self):
         obj = api.create_object(self.ctxt, self.model, {'name': 'foo'})