CODEWITHSUNDEEP
django
Crazy Frog
Crazy Frog

Reputation: 525

Getting model instance by variable model name and pk

I am using Django 1.9, and now trying to override save method behaviour. The problem is that when I do instance.some_field = some_value, the self object is already modified, whereas I need to know that was the original value of some_field. To do this, the only way out seems to be fetching object from database by self's pk.

So I wonder what is GENERIC syntax - if there's any - to fetch instance from the database? By saying GENERIC, I imply that I don't want to explicitly type the model name (like MYMODEL.objects.get(...)), but rather make Django figure out the right model based on target instance's model.

To make the question clearer, let me illustrate my goal in a pseudo-code:

def save_extented(self, *args, **kwargs):
   original_object = (self model).objects.get(pk = self.pk)

Is it possible ? Or maybe I don't need this, and there's some smart Django hack to fetch the instance with rolled back field values ?

Upvotes: 0

Views: 326

Answers (1)

afilardo
afilardo

Reputation: 527

You can use django-dirtyfields and pre_save signal:

@receiver(pre_save, sender=MyModel)
def pre_save_logic(sender, instance, **kwargs):
    if 'my_field' in instance.get_dirty_fields():
        do_some_logic()

Upvotes: 1

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