python - Django BigInteger auto-increment field as primary key?

Question

I'm currently building a project which involves a lot of collective intelligence. Every user visiting the web site gets created a unique profile and their data is later used to calculate best matches for themselves and other users.

By default, Django creates an INT(11) id field to handle models primary keys. I'm concerned with this being overflown very quickly (i.e. ~2.4b devices visiting the page without prior cookie set up). How can I change it to be represented as BIGINT in MySQL and long() inside Django itself?

I've found I could do the following (http://docs.djangoproject.com/en/dev/ref/models/fields/#bigintegerfield):

class MyProfile(models.Model):
    id = BigIntegerField(primary_key=True)

But is there a way to make it autoincrement, like usual id fields? Additionally, can I make it unsigned so that I get more space to fill in?

Thanks!

Answer 1

Inspired by lfagundes but with a small but important correction:

class BigAutoField(fields.AutoField):
    def db_type(self, connection):  # pylint: disable=W0621
        if 'mysql' in connection.__class__.__module__:
            return 'bigint AUTO_INCREMENT'
        return super(BigAutoField, self).db_type(connection)

add_introspection_rules([], [r"^a.b.c.BigAutoField"])

Notice instead of extending BigIntegerField, I am extending AutoField. This is an important distinction. With AutoField, Django will retrieve the AUTO INCREMENTed id from the database, whereas BigInteger will not.

One concern when changing from BigIntegerField to AutoField was the casting of the data to an int in AutoField.

Notice from Django's AutoField:

def to_python(self, value):
    if value is None:
        return value
    try:
        return int(value)
    except (TypeError, ValueError):
        msg = self.error_messages['invalid'] % str(value)
        raise exceptions.ValidationError(msg)

and

def get_prep_value(self, value):
    if value is None:
        return None
    return int(value)

It turns out this is OK, as verified in a python shell:

>>> l2 = 99999999999999999999999999999
>>> type(l2)
<type 'long'>
>>> int(l2)
99999999999999999999999999999L
>>> type(l2)
<type 'long'>
>>> type(int(l2))
<type 'long'>

In other words, casting to an int will not truncate the number, nor will it change the underlying type.