#33517: Implied behavior of `__second` extractor inside of `F()` expressions
does
not match documented behavior for at least PostgreSQL
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Reporter: josefdlange | Owner: nobody
Type: Bug | Status: new
Component: Documentation | Version: 4.0
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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In the Django documentation
(https://docs.djangoproject.com/en/4.0/ref/models/querysets/#second) the
`__second` extractor is implied to be dealing with integer values for
second in a date time. In at least PostgreSQL, the values from
`EXTRACT`ing `second` from a date time will include "any fractional
seconds" (https://www.postgresql.org/docs/current/functions-datetime.html
#FUNCTIONS-DATETIME-EXTRACT) which means it could be more specific than an
integer.
Because of the implication in Django's documentation, I had expected this
filter to work as expected for a row whose `date_created` and
`date_modified` are within a second of each other but a couple of
milliseconds off:
`.filter(date_created__second=F("date_modified__second"))`
However, that ends up not being true given the Postgres behavior.
My recommendation is merely a documentation update to highlight the
discrepancy of behavior between a value coalesced to Python from the DB
data, and how the column values are perceived on the database side within
a query. I'm struggling for adequate language to explain in such a
context, though :-P happy to discuss further and work together toward this
improvement.
--
Ticket URL: <https://code.djangoproject.com/ticket/33517>
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