Re: [Django] #16745: Different times on fields with auto_now and auto_now_add

[Django]

#16745: Different times on fields with auto_now and auto_now_add
-+-
 Reporter:  kantntreiber@…   |Owner:
 |  michaelmior
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  wontfix
 Keywords:  auto_now,| Triage Stage:  Accepted
  auto_now_add, DateTimeField,   |
  DateField, field   |
Has patch:  1|  Needs documentation:  1
  Needs tests:  0|  Patch needs improvement:  1
Easy pickings:  0|UI/UX:  0
-+-
Changes (by claudep):

 * status:  new => closed
 * resolution:   => wontfix


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Re: [Django] #16745: Different times on fields with auto_now and auto_now_add

[Django]

#16745: Different times on fields with auto_now and auto_now_add
-+-
 Reporter:  kantntreiber@…   |Owner:
 |  michaelmior
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.3
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:  auto_now,| Triage Stage:  Accepted
  auto_now_add, DateTimeField,   |
  DateField, field   |
Has patch:  1|  Needs documentation:  1
  Needs tests:  0|  Patch needs improvement:  1
Easy pickings:  0|UI/UX:  0
-+-

Comment (by timgraham):

 Maybe it's worth closing this ticket now that we can use
 [https://docs.djangoproject.com/en/stable/ref/models/database-
 functions/#now database functions], e.g. `default=NOW`. I think `auto_now`
 and `auto_now_add` are somewhat discouraged these days (#22995).

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Re: [Django] #16745: Different times on fields with auto_now and auto_now_add

[Django]

#16745: Different times on fields with auto_now and auto_now_add
-+-
 Reporter:  kantntreiber@…   |Owner:
 Type:  Bug  |  michaelmior
Component:  Database layer   |   Status:  new
  (models, ORM)  |  Version:  1.3
 Severity:  Normal   |   Resolution:
 Keywords:  auto_now,| Triage Stage:  Accepted
  auto_now_add, DateTimeField,   |  Needs documentation:  1
  DateField, field   |  Patch needs improvement:  1
Has patch:  1|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by michaelmior):

 I suppose it could be helpful for debugging purposes and correlating logs.
 And maybe especially so in the case where one needs to integrate with
 legacy systems. The ability to use database time could be a plus. Although
 it seems like other parts for the core would need to be changed to have a
 consistent view of time. Actually. perhaps it would be easiest to allow
 {{{TIME_ZONE}}} to be configured such that it will use the DB server's TZ.
 In any case, this feels outside the scope of this issue, but I'm open to
 continuing work on something along these lines if it proves useful.

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Re: [Django] #16745: Different times on fields with auto_now and auto_now_add

[Django]

#16745: Different times on fields with auto_now and auto_now_add
-+-
 Reporter:  kantntreiber@…   |Owner:
 Type:  Bug  |  michaelmior
Component:  Database layer   |   Status:  new
  (models, ORM)  |  Version:  1.3
 Severity:  Normal   |   Resolution:
 Keywords:  auto_now,| Triage Stage:  Accepted
  auto_now_add, DateTimeField,   |  Needs documentation:  1
  DateField, field   |  Patch needs improvement:  1
Has patch:  1|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by akaariai):

 In the case of PostgreSQL, the server configured time zone doesn't matter,
 the time zone used in the connection is what matters. And Django knows
 that.

 But I might be pushing this a bit too far, maybe using database.now()
 should be a separate field option, and done in separate ticket. I am not
 sure if transaction start time is easily available when using other
 databases.

 It seems I will be really busy at least until weekend. Have to see if I
 can find time to review this.

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Re: [Django] #16745: Different times on fields with auto_now and auto_now_add

[Django]

#16745: Different times on fields with auto_now and auto_now_add
-+-
 Reporter:  kantntreiber@…   |Owner:
 Type:  Bug  |  michaelmior
Component:  Database layer   |   Status:  new
  (models, ORM)  |  Version:  1.3
 Severity:  Normal   |   Resolution:
 Keywords:  auto_now,| Triage Stage:  Accepted
  auto_now_add, DateTimeField,   |  Needs documentation:  1
  DateField, field   |  Patch needs improvement:  1
Has patch:  1|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by michaelmior):

 @aaugustin Would I be correct in understanding that
 {{{django.utils.timezone.localtime}}} performs the conversion to the
 default time zone?

 @kaaria Agreed that the transaction start time may be unreliable, but it
 should be roughly accurate. As far as I can tell, Django has no guarantees
 on the delta of these times from their actual values anyway. (Although
 perhaps calling the time {{{transaction_start}}} is a bit of a misnomer.)
 My concern with using `NOW()` from the database end is that it requires
 knowledge of the server's configured time zone, which I don't believe
 Django currently has. Correct me if I'm wrong.

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Re: [Django] #16745: Different times on fields with auto_now and auto_now_add

[Django]

#16745: Different times on fields with auto_now and auto_now_add
-+-
 Reporter:  kantntreiber@…   |Owner:
 Type:  Bug  |  michaelmior
Component:  Database layer   |   Status:  new
  (models, ORM)  |  Version:  1.3
 Severity:  Normal   |   Resolution:
 Keywords:  auto_now,| Triage Stage:  Accepted
  auto_now_add, DateTimeField,   |  Needs documentation:  1
  DateField, field   |  Patch needs improvement:  1
Has patch:  1|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by akaariai):

 I will try to get some time reviewing this patch. Recording the
 transaction start time reliably could be surprisingly hard, as generally
 Django has pretty bad knowledge of when in transaction and when not. But
 it seems the proposed patch will work.

 I would like it even more if there were some way to get the actual
 database transaction start time ("SELECT now()" in PostgreSQL). But even
 as is, I think this patch has merit.

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Re: [Django] #16745: Different times on fields with auto_now and auto_now_add

[Django]

#16745: Different times on fields with auto_now and auto_now_add
-+-
 Reporter:  kantntreiber@…   |Owner:
 Type:  Bug  |  michaelmior
Component:  Database layer   |   Status:  new
  (models, ORM)  |  Version:  1.3
 Severity:  Normal   |   Resolution:
 Keywords:  auto_now,| Triage Stage:  Accepted
  auto_now_add, DateTimeField,   |  Needs documentation:  1
  DateField, field   |  Patch needs improvement:  1
Has patch:  1|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-

Comment (by aaugustin):

 DateFields and TimeFiles are naive – they don't store timezone information
 – while DateTimeField is aware.

 You should convert timezone.now() to the default time zone before
 extracting the date or time part.

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Re: [Django] #16745: Different times on fields with auto_now and auto_now_add

[Django]

#16745: Different times on fields with auto_now and auto_now_add
-+-
 Reporter:  kantntreiber@…   |Owner:
 Type:  Bug  |  michaelmior
Component:  Database layer   |   Status:  new
  (models, ORM)  |  Version:  1.3
 Severity:  Normal   |   Resolution:
 Keywords:  auto_now,| Triage Stage:  Accepted
  auto_now_add, DateTimeField,   |  Needs documentation:  1
  DateField, field   |  Patch needs improvement:  1
Has patch:  1|UI/UX:  0
  Needs tests:  0|
Easy pickings:  0|
-+-
Changes (by michaelmior):

 * cc: michaelmior (added)
 * needs_better_patch:  0 => 1
 * has_patch:  0 => 1
 * owner:  nobody => michaelmior
 * needs_docs:  0 => 1


Comment:

 Apologies for the poorly named initial patch attachment. (Can't seem to
 delete.) This is my first time attempting a contribution to Django. I
 attached a patch which is working for me. However, I'm not quite sure how
 this interacts with the newly-introduced timezone-aware times.

 I noticed for DateField and TimeField, the current date/time is derived
 from datetime (i.e. {{{datetime.date.today()}}} or
 {{{datetime.datetime.now().time()}}}), but for DateTimeField, the time
 comes from {{{timezone.now()}}}. Is this a bug also, or is there a reason
 for this I'm not aware of.

 Anyway, the patch likely needs some work since I'm not too familiar with
 the Django core, but I'm happy to help :)

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Re: [Django] #16745: Different times on fields with auto_now and auto_now_add

[Django]

#16745: Different times on fields with auto_now and auto_now_add
-+-
   Reporter: |  Owner:  nobody
  kantntreiber@… | Status:  new
   Type:  Bug|  Component:  Database layer
  Milestone: |  (models, ORM)
Version:  1.3|   Severity:  Normal
 Resolution: |   Keywords:  auto_now,
   Triage Stage:  Accepted   |  auto_now_add, DateTimeField,
Needs documentation:  0  |  DateField, field
Patch needs improvement:  0  |  Has patch:  0
  UI/UX:  0  |Needs tests:  0
 |  Easy pickings:  0
-+-
Changes (by akaariai):

 * needs_better_patch:   => 0
 * needs_docs:   => 0
 * needs_tests:   => 0
 * stage:  Unreviewed => Accepted


Comment:

 Accepted because, yes, it would be nice if the times matched. However I
 believe this will not get fixed soon, as there isn't a trivial (as in one-
 liner) fix, and for most developers this doesn't have a high priority.
 Unless of course somebody interested in fixing this creates a clean patch
 with tests.

 To get me interested in this ticket, an approach which would go along the
 lines of:
   - Record transaction start time in Django (something like PostgreSQL
 now())
   - Use that time in auto_now and auto_now_add

 In my opinion the approach is a good one because transaction start time
 has other uses than solving this ticket's problem, and it would be
 hopefully easy to solve this ticket's problem as a trivial one-liner as a
 side effect of having the transaction start time available. In addition,
 the transaction start time would make all objects saved in one transaction
 have the same time.

 Then again, I don't know if core developers would be interested in this
 approach...

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[Django] #16745: Different times on fields with auto_now and auto_now_add

[Django]

#16745: Different times on fields with auto_now and auto_now_add
-+-
 Reporter:  kantntreiber@…   |  Owner:  nobody
 Type:  Bug  | Status:  new
Milestone:   |  Component:  Database layer
  Version:  1.3  |  (models, ORM)
 Keywords:  auto_now, auto_now_add,  |   Severity:  Normal
  DateTimeField, DateField, field|   Triage Stage:  Unreviewed
Has patch:  0|  Easy pickings:  0
UI/UX:  0|
-+-
 There is a little issue with using "auto_now" and "auto_now_add" together
 in one model. Because the time is set by calling datetime.now() in the
 pre_save method of the field, using together more than one such field
 would lead to different values for every field. This is bad, as one
 expects that the time is the time of the creation or change of the object
 and therefore should be identical across all of its fields.

 An example:

 {{{
 class FooModel(models.Model):
 time_changed = models.DateTimeField(auto_now=True)
 time_created = models.DateTimeField(auto_now_add=True)


 In [3]: from models import FooModel

 In [4]: o=FooModel()

 In [5]: o.time_changed

 In [6]: o.save()

 In [7]: o.time_changed
 Out[7]: datetime.datetime(2011, 9, 2, 11, 21, 37, 582956)

 In [8]: o.time_created
 Out[8]: datetime.datetime(2011, 9, 2, 11, 21, 37, 582857)
 }}}

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