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auto_now using signals

Author:
ddanier
Posted:
July 10, 2008
Language:
Python
Version:
.96
Tags:
datetime model auto_now
Score:
-2 (after 4 ratings)

There has been some discussion about removing auto_now and auto_now_add some time ago. auto_now_add can be replaced be using a callable default value, auto_now can't. So I wrote this litte function for my current project (older ones still use auto_add) to fill the gap...but I'm not sure if auto_now will be removed at all.

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# Takes model and fieldname and sets field to current datetime on pre_save
def auto_now_on_save(model, fieldname):
	from django.db.models import signals
	from django.dispatch import dispatcher
	def _update_datefield(instance):
		from datetime import datetime
		setattr(instance, fieldname, datetime.now())
	dispatcher.connect(_update_datefield, signal=signals.pre_save, sender=model, weak=False)

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Comments

ericflo (on July 10, 2008):

It's good to know that for now that Django's signals are a fairly large performance hit. To remedy this, you can simply do this:

def save(self):
    self.myfield = datetime.now()
    super(MyModel, self).save()

It's one more line than if you import your solution and apply it to a field, but doesn't incur the performance penalty that signals currently entail.

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