[openstack-dev] [oslo.db] Proposal: Get rid of deleted column
jaypipes at gmail.com
Tue Aug 20 14:33:48 UTC 2013
*sigh* I wish I'd been aware of these conversations and been in the
Grizzly summit session on soft delete...
What specific unique constraint was needed that changing the deleted
column to use the id value solved?
On 08/19/2013 03:56 AM, Chris Behrens wrote:
> '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()
>> 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):
>> service = relationship(Service,
>> '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 ;)
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