# 59 ORM層面刪除數據注意事項 ORM層面刪除數據，會無視mysql級別的外鍵約束，直接會對將對應的數據刪除，然后將從表中的那個外鍵設置為NULL,如果想要避免這種行為，應該將從表中的外鍵的"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) # 會起到限制 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() # 刪除user表，article表的外鍵修改為null session.delete(user) session.commit() ```