@staticmethod
    def _from_db_object(context, instance, db_inst, expected_attrs=None):
        instance._context = context
        if expected_attrs is None:
            expected_attrs = []
        # Most of the field names match right now, so be quick
        for field in instance.fields:
            if field in INSTANCE_OPTIONAL_ATTRS:
                continue
            elif field == 'deleted':
                instance.deleted = db_inst['deleted'] == db_inst['id']
            elif field == 'cleaned':
                instance.cleaned = db_inst['cleaned'] == 1
            else:
                instance[field] = db_inst[field]

        # NOTE(danms): We can be called with a dict instead of a
        # SQLAlchemy object, so we have to be careful here
        if hasattr(db_inst, '__dict__'):
            have_extra = 'extra' in db_inst.__dict__ and db_inst['extra']
        else:
            have_extra = 'extra' in db_inst and db_inst['extra']

        if 'metadata' in expected_attrs:
            instance['metadata'] = utils.instance_meta(db_inst)
        if 'system_metadata' in expected_attrs:
            instance['system_metadata'] = utils.instance_sys_meta(db_inst)
        if 'fault' in expected_attrs:
            instance['fault'] = (
                objects.InstanceFault.get_latest_for_instance(
                    context, instance.uuid))
        if 'numa_topology' in expected_attrs:
            if have_extra:
                instance._load_numa_topology(
                    db_inst['extra'].get('numa_topology'))
            else:
                instance.numa_topology = None
        if 'pci_requests' in expected_attrs:
            if have_extra:
                instance._load_pci_requests(
                    db_inst['extra'].get('pci_requests'))
            else:
                instance.pci_requests = None
        if 'vcpu_model' in expected_attrs:
            if have_extra:
                instance._load_vcpu_model(
                    db_inst['extra'].get('vcpu_model'))
            else:
                instance.vcpu_model = None
        if 'ec2_ids' in expected_attrs:
            instance._load_ec2_ids()
        if 'migration_context' in expected_attrs:
            if have_extra:
                instance._load_migration_context(
                    db_inst['extra'].get('migration_context'))
            else:
                instance.migration_context = None
        if 'info_cache' in expected_attrs:
            if db_inst.get('info_cache') is None:
                instance.info_cache = None
            elif not instance.obj_attr_is_set('info_cache'):
                # TODO(danms): If this ever happens on a backlevel instance
                # passed to us by a backlevel service, things will break
                instance.info_cache = objects.InstanceInfoCache(context)
            if instance.info_cache is not None:
                instance.info_cache._from_db_object(context,
                                                    instance.info_cache,
                                                    db_inst['info_cache'])

        if any([x in expected_attrs for x in ('flavor',
                                              'old_flavor',
                                              'new_flavor')]):
            if have_extra and db_inst['extra'].get('flavor'):
                instance._flavor_from_db(db_inst['extra']['flavor'])

        # TODO(danms): If we are updating these on a backlevel instance,
        # we'll end up sending back new versions of these objects (see
        # above note for new info_caches
        if 'pci_devices' in expected_attrs:
            pci_devices = base.obj_make_list(
                    context, objects.PciDeviceList(context),
                    objects.PciDevice, db_inst['pci_devices'])
            instance['pci_devices'] = pci_devices
        if 'security_groups' in expected_attrs:
            sec_groups = base.obj_make_list(
                    context, objects.SecurityGroupList(context),
                    objects.SecurityGroup, db_inst.get('security_groups', []))
            instance['security_groups'] = sec_groups

        if 'tags' in expected_attrs:
            tags = base.obj_make_list(
                context, objects.TagList(context),
                objects.Tag, db_inst['tags'])
            instance['tags'] = tags

        if 'services' in expected_attrs:
            services = base.obj_make_list(
                    context, objects.ServiceList(context),
                    objects.Service, db_inst['services'])
            instance['services'] = services

        instance.obj_reset_changes()
        return instance
Method to help with migration to objects.
dataset/ETHPy150Open BU-NU-CLOUD-SP16/Trusted-Platform-Module-nova/nova/objects/instance.py/Instance._from_db_object