#36876: Model timestamp fields get different values using auto_now
-------------------------------------+-------------------------------------
Reporter: Thomas Drevon | Owner: (none)
Type: Bug | Status: new
Component: Database layer | Version: 5.2
(models, ORM) |
Severity: Normal | Resolution:
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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Description changed by Thomas Drevon:
Old description:
> I have a BaseModel, which I use to set created_at and updated_at. Like
> so:
>
> {{{
> class BaseModel(models.Model):
> id = models.CharField(primary_key=True, max_length=50,
> default=generate_nanoid, editable=False)
> created_at = models.DateTimeField(auto_now_add=True)
> updated_at = models.DateTimeField(auto_now=True)
> }}}
>
> When a row is created in one of my tables, both created_at and udpated_at
> fields are set. Which is expected. What is ''not'' expected, is that the
> created_at field gets a slightly older value than the updated_at field.
> Typically:
>
> created_at: 2026-01-22 08:53:38.479806+00
> updated_at: 2026-01-22 08:53:38.479828+00
>
> This is, in my opinion, a bug. Because create happens (I presume) in a
> single transaction. And also because these fields when, compared for
> similiarty, should reveal if the row has been updated at some later time.
>
> As a workaround, one could override the model save method like so:
>
> {{{
> def save(self, *args, **kwargs):
> """Ensure created_at and updated_at are identical on creation"""
> if self._state.adding:
> now = timezone.now()
> if not self.created_at:
> self.created_at = now
> self.updated_at = self.created_at
> super().save(*args, **kwargs)
> }}}
>
> This should probably get attention because it might be a symptom of
> inconsistent timestamp usage during create?
>
> (My exact django version is v5.2.9)
New description:
I have a BaseModel, which I use to set created_at and updated_at. Like so:
{{{
class BaseModel(models.Model):
id = models.CharField(primary_key=True, max_length=50,
default=generate_nanoid, editable=False)
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
}}}
When a row is created in one of my tables, both created_at and udpated_at
fields are set. Which is expected. What is ''not'' expected, is that the
created_at field gets a slightly older value than the updated_at field.
Typically:
created_at: 2026-01-22 08:53:38.479806+00
updated_at: 2026-01-22 08:53:38.479828+00
This is, in my opinion, a bug. Because create happens (I presume) in a
single transaction. And also because these fields when, compared for
similiarty, should reveal if the row has been updated at some later time.
As a workaround, one could override the model save method like so:
{{{
def save(self, *args, **kwargs):
"""Ensure created_at and updated_at are identical on creation"""
now = timezone.now()
if self._state.adding:
# On creation, set both to the same timestamp
if not self.created_at:
self.created_at = now
self.updated_at = self.created_at
else:
# On update, only touch updated_at
self.updated_at = now
super().save(*args, **kwargs)
}}}
This should probably get attention because it might be a symptom of
inconsistent timestamp usage during create?
(My exact django version is v5.2.9)
--
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Ticket URL: <https://code.djangoproject.com/ticket/36876#comment:1>
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