[placement] Fix resource provider delete

Due to foreign key constraints for the
resource_provider.root_provider_id in mysql and the way of column
filling it is impossible to delete newly created RP now.

Patch sets root_provider_id to NULL before deletion
if root_provider_id == id.

Closes-Bug: #1739571
Co-Authored-by: Andrey Volkov <avolkov@mirantis.com>
Change-Id: I256c901fdc02b1f764ea9f8d1a1a708e82cc369a

nova/objects/resource_provider.py

@@ -644,6 +644,13 @@ def _provider_ids_from_uuid(context, uuid):
     return ProviderIds(**dict(res))
 
 
+@db_api.api_context_manager.writer
+def _delete_rp_record(context, _id):
+    return context.session.query(models.ResourceProvider).\
+        filter(models.ResourceProvider.id == _id).\
+        delete(synchronize_session=False)
+
+
 @base.NovaObjectRegistry.register_if(False)
 class ResourceProvider(base.NovaObject, base.NovaTimestampObject):
     SETTABLE_FIELDS = ('name', 'parent_provider_uuid')
@@ -841,11 +848,14 @@ class ResourceProvider(base.NovaObject, base.NovaTimestampObject):
         RPT_model = models.ResourceProviderTrait
         context.session.query(RPT_model).\
                 filter(RPT_model.resource_provider_id == _id).delete()
+        # set root_provider_id to null to make deletion possible
+        context.session.query(models.ResourceProvider).\
+            filter(models.ResourceProvider.id == _id,
+                   models.ResourceProvider.root_provider_id == _id).\
+            update({'root_provider_id': None})
         # Now delete the RP record
         try:
-            result = context.session.query(models.ResourceProvider).\
-                     filter(models.ResourceProvider.id == _id).\
-                     delete(synchronize_session=False)
+            result = _delete_rp_record(context, _id)
         except sqla_exc.IntegrityError:
             # NOTE(jaypipes): Another thread snuck in and parented this
             # resource provider in between the above check for

nova/tests/unit/objects/test_resource_provider.py

@@ -17,6 +17,7 @@ from oslo_utils import timeutils
 
 import nova
 from nova import context
+from nova.db.sqlalchemy import api_models as models
 from nova import exception
 from nova.objects import fields
 from nova.objects import resource_provider
@@ -219,6 +220,29 @@ class TestResourceProvider(test_objects._LocalTest):
                           resource_provider.ResourceProvider.get_by_uuid,
                           self.context, uuids.rp)
 
+    def test_destroy(self):
+
+        def emulate_rp_mysql_delete(func):
+            def wrapped(context, _id):
+                rp = context.session.query(
+                    models.ResourceProvider).\
+                    filter(
+                        models.ResourceProvider.id == _id).first()
+                self.assertIsNone(rp.root_provider_id)
+                return func(context, _id)
+            return wrapped
+
+        emulated = emulate_rp_mysql_delete(resource_provider._delete_rp_record)
+
+        rp = resource_provider.ResourceProvider(
+            self.context, uuid=_RESOURCE_PROVIDER_UUID,
+            name=_RESOURCE_PROVIDER_NAME)
+        rp.create()
+
+        with mock.patch.object(
+                resource_provider, '_delete_rp_record', emulated):
+            rp.destroy()
+
 
 class TestInventoryNoDB(test_objects._LocalTest):
     USES_DB = False