Enable defaults for cell_v2 update_cell command

Initialize optional parameters for update_cell() to None and
enable getting the transport_url and db_connection from
nova.conf if not specified as arguments.

Change-Id: Ib20cfeb7b17dba06f9f2db5eca1fa194d2795767
Closes-Bug: 1665145
(cherry picked from commit b276e84103)

doc/source/man/nova-manage.rst

@@ -165,10 +165,14 @@ Nova Cells v2
 
 ``nova-manage cell_v2 update_cell --cell_uuid <cell_uuid> [--name <cell_name>] [--transport-url <transport_url>] [--database_connection <database_connection>]``
 
-    Updates the properties of a cell by the given uuid. If the cell is not
-    found by uuid, this command will return an exit code of 1. If the
-    properties cannot be set, this will return 2. Otherwise, the exit code
-    will be 0.
+    Updates the properties of a cell by the given uuid. If a
+    database_connection is not specified, it will attempt to use the one
+    defined by ``[database]/connection`` in the configuration file.  If a
+    transport_url is not specified, it will attempt to use the one defined
+    by ``[DEFAULT]/transport_url`` in the configuration file. If the cell
+    is not found by uuid, this command will return an exit code of 1. If
+    the properties cannot be set, this will return 2. Otherwise, the exit
+    code will be 0.
 
     NOTE: Updating the transport_url or database_connection fields on
     a running system will NOT result in all nodes immediately using the

nova/cmd/manage.py

@@ -1506,7 +1506,8 @@ class CellV2Commands(object):
     @args('--database_connection', metavar='<database>', dest='db_connection',
           help=_('Set the cell database_connection. NOTE that running nodes '
                  'will not see the change until restart!'))
-    def update_cell(self, cell_uuid, name, transport_url, db_connection):
+    def update_cell(self, cell_uuid, name=None, transport_url=None,
+                    db_connection=None):
         """Updates the properties of a cell by the given uuid.
 
         If the cell is not found by uuid, this command will return an exit
@@ -1526,8 +1527,12 @@ class CellV2Commands(object):
 
         if name:
             cell_mapping.name = name
+
+        transport_url = transport_url or CONF.transport_url
         if transport_url:
             cell_mapping.transport_url = transport_url
+
+        db_connection = db_connection or CONF.database.connection
         if db_connection:
             cell_mapping.database_connection = db_connection
 

nova/tests/unit/test_nova_manage.py

@@ -1564,6 +1564,22 @@ class CellV2CommandsTestCase(test.NoDBTestCase):
         output = self.output.getvalue().strip()
         self.assertEqual('', output)
 
+    def test_update_cell_success_defaults(self):
+        ctxt = context.get_admin_context()
+        objects.CellMapping(context=ctxt, uuid=uuidsentinel.cell1,
+                            name='cell1',
+                            transport_url='fake://mq',
+                            database_connection='fake:///db').create()
+        self.assertEqual(0, self.commands.update_cell(uuidsentinel.cell1))
+        cm = objects.CellMapping.get_by_uuid(ctxt, uuidsentinel.cell1)
+        self.assertEqual('cell1', cm.name)
+        expected_transport_url = CONF.transport_url or 'fake://mq'
+        self.assertEqual(expected_transport_url, cm.transport_url)
+        expected_db_connection = CONF.database.connection or 'fake:///db'
+        self.assertEqual(expected_db_connection, cm.database_connection)
+        output = self.output.getvalue().strip()
+        self.assertEqual('', output)
+
 
 class TestNovaManageMain(test.NoDBTestCase):
     """Tests the nova-manage:main() setup code."""