# 59 ORM层面删除数据注意事项 ORM层面删除数据，会无视mysql级别的外键约束，直接会对将对应的数据删除，然后将从表中的那个外键设置为NULL,如果想要避免这种行为，应该将从表中的外键的"nullable=False" ```text class User(Base): __tablename__ = "user" id = Column(Integer,primary_key=True,autoincrement=True) username = Column(String(50),nullable=False) class Article(Base): __tablename__ = "article" id = Column(Integer,primary_key=True,autoincrement=True) title = Column(String(50),nullable=False) # 会起到限制 uid = Column(Integer,ForeignKey('user.id'),nullable=False) # uid = Column(Integer,ForeignKey('user.id')) author = relationship("User",backref="articles") # Base.metadata.drop_all() # Base.metadata.create_all() # # user = User(username = 'angle1') # article = Article(title = 'angle2') # # article.author = user # # session.add(article) # session.commit() user = session.query(User).first() # 删除user表，article表的外键修改为null session.delete(user) session.commit() ```