Override save method for every class in models.Model - django

Question

I need to get every class, that inherits models.Model to have created and updated field. I can achieve this by adding custom save method to every field,
def save(self, *args, **kwargs):
if not self.id:
self.created = timezone.now()
self.modified = timezone.now()
return super(`models.Model`, self).save(*args, **kwargs)
but this violates Don'tRepeatYourself rule.
I've tried to override models.Model:
class LogModel(models.Model):
created = models.DateTimeField(editable=False)
updated = models.DateTimeField()
def save(self, *args, **kwargs):
if not self.id:
self.created = timezone.now()
self.updated = timezone.now()
return super(LogModel, self).save(*args, **kwargs)
and use LogModel instead of models.Model, but this failed with error E006(
The field 'x' clashes with the field 'x' from model 'y.logmodel'.
EDIT
My main question is how to add a custom specific field to all models in my models.py

Answer 1

Your base model must be abstract:
class LogModel(models.Model):
class Meta:
abstract = True
created = models.DateTimeField(editable=False)
updated = models.DateTimeField()
def save(self, force_insert=False, force_update=False, using=None, update_fields=None):
# Use self._state.adding to check if this is a new instance,
# ID not being empty is not a guarantee that the instance
# exists in the database
# and if `update_fields` is passed, you must add the fields to the
# list or they won't be saved in the database.
if force_insert or self._state.adding:
self.created = timezone.now()
if update_fields and 'created' not in update_fields:
update_fields.append('created')
self.updated = timezone.now()
if update_fields and 'updated' not in update_fields:
update_fields.append('updated')
return super(LogModel, self).save(*args, **kwargs)
However, if you override the save() method, this means it won't be editable in any form. If this is what you want, then you are better to use auto_now and auto_now_add:
class LogModel(models.Model):
class Meta:
abstract = True
created = models.DateTimeField(auto_now_add=True)
updated = models.DateTimeField(auto_now=True)

Answer 2

Instead of overriding save method, you could define auto_now_add and auto_now parameters in the Model field like:
created = models.DateTimeField(auto_now_add=True)
updated = models.DateTimeField(auto_now=True)
For more information on these parameters, you can check the django docs.

Answer 3

It can be done by defining Abstract Base Model and define save method there and create all the models by inheriting from the abstract class. e.g.
class MyAbstractModel(models.Model):
created = models.DateTimeField(editable=False)
updated = models.DateTimeField()
def save(self, *args, **kwargs):
if self._state.adding:
self.created = timezone.now()
self.updated = timezone.now()
return super(LogModel, self).save(*args, **kwargs)
class Meta:
abstract = True
and create child model class from it:
class Record(MyAbstractModel):
pass

Answer 4

Unfortunately, using update_fields in .save() does not trigger fields with auto_now, so I overridden save method this way:
class BaseModel(models.Model):
class Meta:
abstract = True
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
_base_update_fields = ['updated_at']
def save(
self, force_insert=False, force_update=False,
using=None, update_fields=None
):
_update_fields = None
if update_fields is not None:
_update_fields = self._base_update_fields + update_fields
super().save(
force_insert=force_insert, force_update=force_update,
using=using, update_fields=_update_fields
)