Flask一对多级联删除，需要在反向关系中添加cascade='all, delete-orphan'参数，实列如下：

class Person(db.Model) :
    __tablename__ = 'person'
    id = db.Column(db.Integer, primary_key = True)
    name = db.Column(db.String(32))
# 添加cascade='all, delete-orphan'参数
    books = db.relationship('Book', backref='person', lazy='dynamic',cascade='all, delete-orphan')
    
class Book(db.Model) :
    __tablename__ = 'book '
    id = db.Column(db.Integer, primary_key = True)
    name = db.Column(db.String(32))
# 外键添加ondelete='CASCADE')属性
    person_id = db.Column(db.Integer, db.ForeignKey('person.id',ondelete='CASCADE'))