inheritance - Determining Django Model Instance Types after a Query on a Base-class

Question

Is there a way to determine what the 'real' class of a Django database object is, after it has been returned from a query for on a base class?

For instance, if I have these models...

class Animal(models.Model):
    name= models.CharField(max_length=128)

class Person(Animal):
    pants_size = models.IntegerField(null=True)

class Dog(Animal):
    panting_rate = models.IntegerField(null=True)

And create these instances...

Person(name='Dave').save()
Dog(name='Mr. Rufflesworth').save()

If I do a query like Animal.objects.all(), I end up with two Animal instances, not an instance of Person and an instance of Dog. Is there any way to determine which instance is of which type?

---

FYI: I already tried doing this...

isinstance(Animal.objects.get(name='Dave'),Person) # <-- Returns false!

But that doesn't seem to work.

Answer 1

We implemented our own cast() function that works quite well (Without ContentType's):

class Base(models.Model):
    """
    If your class needs the basics, like created date, modified date etc, then
    inherit from this Base class.
    """
    created = models.DateTimeField(_('Created'), auto_now_add=True)
    modified = models.DateTimeField(_('Modified'), auto_now=True)

    class Meta:
        abstract = True

    def __str__(self):
        return '%s [%s]' % (self.__class__.__name__, self.id)

    def get_class_name(self):
        return str(self.__class__.__name__).lower()

    def to_json(self, include_related=True):
        return {
            'id': self.id,
            'created': self.created.isoformat(),
            'modified': self.modified.isoformat(),
            'class_name': self.__class__.__name__
        }

    def cast(self):
        """
        This method is quite handy, it converts "self" into its correct child class. For example:

        .. code-block:: python

           class Fruit(models.Model):
               name = models.CharField()

           class Apple(Fruit):
               pass

           fruit = Fruit.objects.get(name='Granny Smith')
           apple = fruit.cast()

        :return self: A casted child class of self
        """
        for name in dir(self):
            try:
                attr = getattr(self, name)
                if isinstance(attr, self.__class__):
                    return attr
            except:
                pass
        return self