Use method of model class within save method

Question

I'm trying to override the save method of one of my models. Within that save method I would like to use another method of the model, like this:

class MyModel(models.Model):
    name = models.CharField(max_length=255)

    def do_something(self):
        pass

    def save(self,*args, **kwargs):
        self.do_something()
        super(MyModel, self).save(*args, **kwargs)

This doesn't work because when django executes the save, the object is a generic ModelBase class and not my subclass of ModeBase. So I get:

unbound method do_something() must be called with MyModel instance as first argument (got ModelBase instance instead)

What is the right way to do this?

Can you call the method super(MyModel, self).save(*args, **kwargs) before you call self.do_something()? So just switch the two so that the object will get created first. — nates
– nates, Commented May 25, 2012 at 23:05
I have tried that--it doesn't seem to help. Also, I'd like to make sure the 'do_something' completes successfully before I save the model. — prauchfuss
– prauchfuss, Commented May 26, 2012 at 19:15

juliomalegria · Accepted Answer · 2012-05-26 04:41:55Z

1

You should put args and kwargs to overridden save()method too:

class MyModel(models.Model):
    name = models.CharField(max_length=255)

    def do_something(self):
        pass

    def save(self, *args, **kwargs):
        self.do_something()
        super(MyModel, self).save(*args, **kwargs)

You also forgot self parameter in do_something()!

UPDATE

I don't quite understand your problem. If you want to call unbound method do_something, define it outside the class MyModel with one and just call it from save() like `do_something(self):

class MyModel(class.Model):
  def save(self, *args, **kwargs):
    do_something(self)
    super(MyModel, self).save(*args, **kwargs)

def do_someting(my_model_instance):
  assert isinstance(my_model_instance, MyModel)
  ...

edited May 26, 2012 at 4:41

juliomalegria

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answered May 25, 2012 at 20:33

Aleš Kotnik

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4 Comments

prauchfuss Over a year ago

Thanks. Should be good now. It's hard debugging made up code!

Aleš Kotnik Over a year ago

Welcome. If that answer solved your problem, consider clicking checkmark to mark this answer Accepted.

prauchfuss Over a year ago

That really doesn't solve the actual problem. We'll see what else comes in.

prauchfuss Over a year ago

That's what I'd like to avoid really. Obviously I can take all my methods outside the model.

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