# 61 relationship方法中的cascade参数详解（2） ```text 续上... from sqlalchemy import create_engine, Column, Integer, Text, String, DateTime, String, Float, func, and_, or_, \ ForeignKey, Table from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker,relationship,backref HOSTNAME = '127.0.0.1' PORT = "3306" USERNAME = "root" PASSWORD = "123456" DATABASE = "xt_flask" DB_URI = "mysql+pymysql://{}:{}@{}:{}/{}?charset=utf8".format(USERNAME,PASSWORD,HOSTNAME,PORT,DATABASE) engine = create_engine(DB_URI) Base = declarative_base(engine) session = sessionmaker(engine)() class User(Base): __tablename__ = 'user' id = Column(Integer,primary_key=True,autoincrement=True) username = Column(String(50),nullable=False) # articles = relationship("Article",cascade="save-update,delete") # comments = relationship('Comment',cascade="save-update,delete") class Article(Base): __tablename__ = 'article' id = Column(Integer,primary_key=True,autoincrement=True) title = Column(String(50),nullable=False) uid = Column(Integer,ForeignKey("user.id")) # 不会执行添加操作 -- not add Article # author = relationship("User",backref="articles",cascade="") # 保存并更新数据 # delete:级删除 # author = relationship("User", backref="articles", cascade="save-update,delete") # author = relationship("User", backref="articles", cascade="delete") # author = relationship("User", cascade="save-update,delete") # single_parent=True,唯一的父表 # cascade="all"，除了delete-orphan都包含了 author = relationship("User", backref=backref("articles",cascade="save-update,delete,delete-orphan,merge,expunge"),cascade="save-update",single_parent=True) class Comment(Base): __tablename__ = "comment" id = Column(Integer,primary_key=True,autoincrement=True) content = Column(Text,nullable=False) uid = Column(Integer,ForeignKey('user.id')) author = relationship("User",backref="comments") def my_init_db(): Base.metadata.drop_all() Base.metadata.create_all() user = User(username="angle") article = Article(title="miku") article.author = user comment = Comment(content="xxxx") comment.author = user session.add(comment) session.add(article) session.commit() def operation(): # article = session.query(Article).first() # session.delete(article) # user = session.query(User).first() # # session.delete(user) # user.articles = [] # user = User(id=1,username="angle2") # article = Article(id=2,title="angle3") # user.articles.append(article) # # 合并，主键重复，替换值，不重复，添加进去 # session.merge(user) # session.merge(article) # 移除操作,与session.add()操作相反 user = User(username="angle2") article = Article(title="angle3") article.author = user session.add(user) session.add(article) # 只会从会话中删除数据，不会从数据库把数据删除 session.expunge(user) session.commit() """ 用户--文章 删除用户可以删除所有文章 删除一遍文章，不会删除用户 """ if __name__ == "__main__": # my_init_db() operation() ```