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[Dan Smith <dms@xxxxxxxxxxxxx>]

I don't think upgrading an object makes any sense. Objects within the
same major version need to be backwards compatible, so sending an object
with a field format change to an older node (or a newer one that can't
cope with it) is not reasonable.

** Changed in: nova
       Status: New => Invalid

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https://bugs.launchpad.net/bugs/1277393

Title:
  unable to transform an old object into a new one with changed types of
  fields

Status in OpenStack Compute (Nova):
  Invalid

Bug description:
  Object Model considers the downgrade but some work in upgrade part are left, so it is  unable to transform an old object into a new one with changed types of fields.
  This problem is related to https://review.openstack.org/#/c/67693/

  Metrics is a string field in computeNode before version 1.3. And we
  make it to be an object field. Then the problem is when the old node
  still sends a string-based set of metrics, it will throw a exception
  in obj_from_primitive due to the type changes.

  AUDIT [nova.service] Starting conductor node (version 2014.1)
  }}}
  Traceback (most recent call last):
    File "nova/tests/objects/test_compute_node.py", line 165, in test_metrics_compat_upgrade
      compute = base.NovaObject.obj_from_primitive(primitive)
    File "nova/objects/base.py", line 246, in obj_from_primitive
      objdata[name]))
    File "nova/objects/fields.py", line 183, in from_primitive
      return self._type.from_primitive(obj, attr, value)
    File "nova/objects/fields.py", line 374, in from_primitive
      return obj_base.NovaObject.obj_from_primitive(value, obj._context)
    File "nova/objects/base.py", line 230, in obj_from_primitive
      if primitive['nova_object.namespace'] != 'nova':
  TypeError: string indices must be integers, not str

  The reason is in version 1.2, the primitive of metrics in compute node is str
  '[{"timestamp": "2014-02-07T08:12:16Z", "name": "cpu.frequency", "value": 1600.0, "source": "libvirt.LibvirtDriver"}]'
  But it should be an object after version 1.3.

  The easiest way to reappear the bug is downloading the patch  https://review.openstack.org/#/c/67693/ and run
  python -m unittest nova.tests.objects.test_compute_node.TestRemoteComputeNodeObject.test_metrics_compat_upgrade

  The test case transforms a new compute_node object into an old one and
  then transforms it into a new one again.

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