#24959: date_interval_sql Implementations for Database Backends Do Not Handle
Negative timedelta Objects Properly
-------------------------------------+-------------------------------------
Reporter: fredpalmer | Owner: nobody
Type: Uncategorized | Status: new
Component: Database layer | Version: 1.8
(models, ORM) |
Severity: Normal | Resolution:
Keywords: date_interval_sql, | Triage Stage:
timedelta, F, orm | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by fredpalmer):
* needs_docs: => 0
* needs_tests: => 0
* needs_better_patch: => 0
Old description:
> If I have a `timedelta` object in python that represents a negative
> difference, e.g.:
>
> {{{
> delta = timedelta(seconds=-3600)
> print delta2
> -1 day, 23:00:00
> }}}
>
> The resultant SQL generated by `date_interval_sql` for the MySQL backend
> would be something like:
>
> {{{
> UPDATE `scheduling_event`
> SET ...
> `my_datetime` = (`my_table`.`my_datetime` + INTERVAL '-1
> 0:0:82800:0' DAY_MICROSECOND),
> WHERE (...)
> }}}
>
> **AND** what we want is the following:
>
> {{{
> UPDATE `scheduling_event`
> SET ...
> `my_datetime` = (`my_table`.`my_datetime` + INTERVAL '-0 0:0:3600:0'
> DAY_MICROSECOND),
> WHERE (...)
> }}}
>
> In layman's terms - the two layers are not convertible in a one-to-one
> sense. A `timedelta` in for the example above in Python means: '''go
> back one day and *add* 23 hours'''. So some `datetime + delta` would
> just subtract one hour.
>
> In MySQL, however, "INTERVAL '-1 0:0:82800:0' DAY_MICROSECOND)" means:
> '''add a negative one day and 23 hours'''.
New description:
If I have a `timedelta` object in python that represents a negative
difference, e.g.:
{{{
delta = timedelta(seconds=-3600)
print delta2
-1 day, 23:00:00
}}}
The resultant SQL generated by `date_interval_sql` for the MySQL backend
would be something like:
{{{
UPDATE `my_table`
SET ...
`my_datetime` = (`my_table`.`my_datetime` + INTERVAL '-1
0:0:82800:0' DAY_MICROSECOND),
WHERE (...)
}}}
**AND** what we want is the following:
{{{
UPDATE `my_table`
SET ...
`my_datetime` = (`my_table`.`my_datetime` + INTERVAL '-0 0:0:3600:0'
DAY_MICROSECOND),
WHERE (...)
}}}
In layman's terms - the two layers are not convertible in a one-to-one
sense. A `timedelta` in for the example above in Python means: '''go back
one day and *add* 23 hours'''. So some `datetime + delta` would just
subtract one hour.
In MySQL, however, ''"INTERVAL '-1 0:0:82800:0' DAY_MICROSECOND)"'' means:
'''add a negative one day and 23 hours'''.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/24959#comment:1>
Django <https://code.djangoproject.com/>
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