I've been using hybrid properties recently and ran into a solution that
would only work on PostgreSQL. That's fine for my usage, but it's so ugly
I was curious if there was a better, more portable way to do this.
Here is the scenario: x minutes before a given date things can happen in my
program. This is used for things like notifications and things where
storing the actual date is more onerous than storing the delta itself.
Here is some code to give an idea (note that this is simplified example
and self.minutes_before could actually come from a different table, so
saving the calculated date would be impractical)
@hybrid_property
def notify_date(self)
return self.date - timedelta(minutes=self.minutes_before)
@notify_date.expression
def notify_date(cls)
return cls.date - cast(cast(cls.minutes_before, Unicode) + ' minutes',
Interval)
So that last part is attempting to mimic this in PostgreSQL:
SELECT date - (minutes_before::varchar || ' minutes')::interval FROM
my_table
So that's it. Anyone aware of a better way to accomplish this? Is there
something in SQLAlchemy that would do something similar to timedelta?
Something like sqlalchemy.interval(minutes=cls.minutes_before) that can
use attributes as well as literals and can translate between databases?
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