def get_prep_value(self, value):
        return self._flatten_value(value)
Given a list of nodes, attach each one's Content. Efficiently.
dataset/ETHPy150Open matthiask/plata/plata/fields.py/JSONField.get_prep_value--crossover with--dataset/ETHPy150Open fusionbox/django-widgy/widgy/models/base.py/Node.attach_content_instances