这是我的类(class):classPresentation(db.Document):title=db.StringField(max_length=120,required=True)author=db.StringField(required=True)pages=db.DocumentField(Page,required=False)tags=db.StringField(max_length=120,required=False)id=db.IntField(required=True)currentPage=db.IntField()def__str__(self):re