*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?
-jay
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 <jaypi...@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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