#2443: Add IntervalField to database models
-------------------------------------+-------------------------------------
Reporter: ben.tucker@… | Owner: mjtamlyn
Type: New feature | Status: assigned
Component: Database layer | Version: master
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: IntervalField | Needs documentation: 0
interval duration DurationField | Patch needs improvement: 1
feature | UI/UX: 1
Has patch: 1 |
Needs tests: 0 |
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Changes (by akaariai):
* needs_better_patch: 0 => 1
Comment:
I think we need support for `qs.filter(event_startdate__gte=datetime.now()
- F('event_duration))`. I think this works on PostgreSQL, but at least on
Oracle it produces wrong results. The event_duration is in microseconds,
but in oracle the date arithmetic interprets integers as days. Actually, I
am not sure if this query works at all.
In any case usages of F('duration_field') need tests. Raising errors from
F() usage is acceptable, but producing wrong results is clearly not OK.
Another issue that keeps nagging me is the use of SubfieldBase to support
value conversion (SubfieldBase basically calls to_python() anytime the
field is set on the object). Other fields in Django core do not use this,
instead they let the backend convert the values. I am not sure if usage of
SubfieldBase leads to any problems, but I keep getting the feeling we
should be consistent in not using SubfieldBase. One case where usage of
backend specific converters differ from usage of to_python + SubfieldBase
is that SubfieldBase does value conversions on assignment. So:
{{{
>>> obj.duration_field = '12:34:56'
>>> obj.duration_field
OUT: '12:34:56' if not using SubfieldBase
OUT: timedelta(12h, 34m, 56s)
}}}
Currently no local field in Django core do value conversions on
assignment. In addition there is clear overhead in model `__init__` when
using SubfieldBase, I'd guess the overhead is somewhere around 20% per
field that uses SubfieldBase, though I haven't benchmarked this.
--
Ticket URL: <https://code.djangoproject.com/ticket/2443#comment:60>
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