I would apply a single event listener to Temporal, and do all the work of
adding the constraints and all that in the one event handler. I'd skip
__table_args__.
If you're on 0.8, you can apply listeners to mixins and unmapped classes using
"propagate=True", and the events should trigger for all subclasses.
On May 23, 2013, at 7:49 AM, Chris Withers <ch...@simplistix.co.uk> wrote:
> Hi All,
>
> I have a mixin defined like this:
>
> def add_exclude_constraint(mapper, class_):
> table = class_.__table__
> elements = [('period', '&&')]
> for col in table.primary_key.columns:
> if col.name!='period':
> elements.append((col, '='))
> table.append_constraint(ExcludeConstraint(*elements))
>
> class Temporal(object):
>
> @declared_attr
> def __table_args__(cls):
> listen(cls, 'instrument_class', add_exclude_constraint)
> return (
> CheckConstraint("period != 'empty'::tsrange"),
> )
>
> period = Column(DateTimeRange(), nullable=False, primary_key=True)
>
> That listen call is the source of the dirty feeling...
>
> What's the "right" way to do this?
>
> Chris
>
> --
> Simplistix - Content Management, Batch Processing & Python Consulting
> - http://www.simplistix.co.uk
>
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