[openstack-dev] [oslo.db] Proposal: Get rid of deleted column

Chris Behrens cbehrens at codestud.com
Mon Aug 19 07:56:29 UTC 2013

'deleted' is used so that we can have proper unique constraints by setting it to `id` on deletion.  This was not the case until Grizzly, and before Grizzly I would have agreed completely.

- Chris

On Aug 19, 2013, at 12:39 AM, Jay Pipes <jaypipes at gmail.com> wrote:

> I'm throwing this up here to get some feedback on something that's always bugged me about the model base used in many of the projects.
> There's a mixin class that looks like so:
> class SoftDeleteMixin(object):
>    deleted_at = Column(DateTime)
>    deleted = Column(Integer, default=0)
>    def soft_delete(self, session=None):
>        """Mark this object as deleted."""
>        self.deleted = self.id
>        self.deleted_at = timeutils.utcnow()
>        self.save(session=session)
> Once mixed in to a concrete model class, the primary join is typically modified to include the deleted column, like so:
> class ComputeNode(BASE, NovaBase):
>    <snip>...
>    service = relationship(Service,
>                           backref=backref('compute_node'),
>                           foreign_keys=service_id,
>                           primaryjoin='and_('
>                                'ComputeNode.service_id == Service.id,'
>                                'ComputeNode.deleted == 0)')
> My proposal is to get rid of the deleted column in the SoftDeleteMixin class entirely, as it is redundant with the deleted_at column. Instead of doing a join condition on deleted == 0, one would instead just do the join condition on deleted_at is None, which translates to the SQL: AND deleted_at IS NULL.
> There isn't much of a performance benefit -- you're only reducing the row size by 4 bytes. But, you'd remove the redundant data from all the tables, which would make the normal form freaks like myself happy ;)
> Thoughts?
> -jay
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