Updating two field from different models simultaneously

Question

I have a problem with keeping the Parent object's modification_date up to date. I want the Parents's modification_date field to update simultaneously with the Child's modification_date field.

class Parent(models.Model):
    modification_date = models.DateTimeField(auto_now=True)
    note = models.ManyToManyField('Child')

class Child(models.Model):
    modification_date = models.DateTimeField(auto_now=True)
    content = models.TextField()

I am using Django.

Answer 1

I would do a post_save signal function. So everytime you update Child Model it will trigger that function and you can change the Parent model:

from django.db.models.signals import post_save

# method for updating
def update_parent(sender, instance, **kwargs):
     parent = Parent.object.get() #the parent you need to update
     parent.modification_date = instance.modification_date
     parent.save()

# register the signal
post_save.connect(update_parent, sender=Child)