def value_from_object(self, obj):
		relobj = super(ForeignKeyAttribute, self).value_from_object(obj)
		return getattr(relobj, 'pk', None)
Converts the default value type (a model instance) to a pk.
dataset/ETHPy150Open ithinksw/philo/philo/models/fields/entities.py/ForeignKeyAttribute.value_from_object