#25363: Model fields pre_save not called if force_insert=True
-------------------------------------+-------------------------------------
Reporter: davidfischer-ch | Owner:
| davidfischer-ch
Type: Bug | Status: closed
Component: Database layer | Version: 1.8
(models, ORM) |
Severity: Normal | Resolution: needsinfo
Keywords: pre_save,save | 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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Comment (by akaariai):
A clean mix-in to track updated fields to both make UPDATE queries
lighter, and to also skip update completely when no data has changed is a
big issue for me. So, if we can make that easier for users, I think we
should do that.
BTW here is my approach for this issue:
{{{
class ModTrackingMixin(object):
@classmethod
def from_db(cls, *args, **kwargs):
new = super().from_db(*args, **kwargs)
new._state.db_vals = new.__dict__.copy()
return new
def save(self, update_fields=None):
if hasattr(self._state, 'db_vals') and update_fields is None:
changed = []
orig = self._state.db_vals
for f, fname in [(f, f.attname) for f in
self._meta.get_fields()
if f.concrete]:
if (fname in orig and
f.to_python(getattr(self, fname)) !=
orig.get(fname, NO_VALUE)):
changed.append(fname)
return super().save(update_fields=changed)
else:
return super().save(update_fields=update_fields)
class Organization(models.Model):
code = models.CharField(max_length=20)
name= models.CharField(max_length=100)
class Meta:
db_table = 'organization'
class ModTrackingOrganization(ModTrackingMixin, Organization):
class Meta:
proxy = True
}}}
The idea is that if you do:
{{{
o = ModTrackingOrganization.objects.first()
o.name = o.name
o.save()
}}}
Then the save will actually be silently skipped (as no data has changed in
the DB).
I wonder if this is actually broken for some cases by the pre_save logic
we have currently in Django?
--
Ticket URL: <https://code.djangoproject.com/ticket/25363#comment:7>
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