Required functionality.

def save(self, obj):
        """Required functionality."""
        if not obj.id:
            obj.id = uuid()

        stored_data = {
            '_id': obj.id,
            'value': json.loads(obj.to_data())
        }

        index_vals = obj.indexes() or {}
        for key in obj.__class__.index_names() or []:
            val = index_vals.get(key, '')
            stored_data[key] = str(val)

        coll = self.get_collection(obj.__class__.get_table_name())
        coll.update({"_id": obj.id}, stored_data, upsert=True)