Fix chunkator when the primary key is a OneToOneField

[zebuline]

django-chunkator orders by pk.

But sometimes, you want to order by an explicit field.

For example:

class ModelA(models.Model):
    name = models.CharField(max_length=20)

    class Meta:
        ordering = ['name']


class ModelB(models.Model):
    modela = models.OneToOneField(ModelA, primary_key=True)

(with django 1.8 ?) when we write this queryset: ModelB.objects.order_by('pk'), it will in background order by modela__name.
We need to order the queryset by modela_id explicitely:

from chunkator import chunkator
for item in chunkator(ModelB.objects.all(), 200, order_by='modela_id'):
    do_something(item)

Edit: it is possible to fix this case without changing the API. See PR #20

[brunobord]

closed by #20