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negative interval encoding issues due to python's timedelta implementation details #1114

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takeda opened this issue Jan 8, 2024 · 1 comment

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@takeda
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takeda commented Jan 8, 2024

  • asyncpg version: 0.29.0
  • PostgreSQL version: 16.1
  • Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
    the issue with a local PostgreSQL install?
    : this is happening on local PG
  • Python version: 3.11.7
  • Platform:
  • Do you use pgbouncer?: no
  • Did you install asyncpg with pip?: yes
  • If you built asyncpg locally, which version of Cython did you use?:
  • Can the issue be reproduced under both asyncio and
    uvloop?
    : yes

Python's timedelta implementation only allows to store negative number of days, hours, minutes, seconds, microseconds are always positive values. So when a negative value smaller than a day is interpreted it is stored in a strange way, example from Python's documentation:

Note that normalization of negative values may be surprising at first. For example:

>>> from datetime import timedelta
>>> d = timedelta(microseconds=-1)
>>> (d.days, d.seconds, d.microseconds)
(-1, 86399, 999999)

https://docs.python.org/3/library/datetime.html?highlight=timedelta#datetime.timedelta

In my particular case when I'm trying to store -3 hours, that's getting translated in python to:

datetime.timedelta(days=-1, seconds=75600)

And ends up stored in postgresql as: "0 years 0 mons -1 days 21 hours 0 mins 0.0 secs"

Is there also a workaround where I can skip timedelta for interval?

@elprans
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elprans commented Jan 9, 2024

Is there also a workaround where I can skip timedelta for interval?

You can set up a custom codec. See an example here

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