准备工作
from sqlalchemy import create_engine, Column, Integer, String, Float, Text, ForeignKeyfrom sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy.orm import sessionmaker, relationship, backref # 数据库信息host = ‘127.0.0.1‘port = ‘3306‘database = ‘db_to_sqlalchemy‘username = ‘root‘password = ‘123456‘ # 数据库类型+连接数据库的插件,这里使用的pymysqlDB_URI = f‘mysql+pymysql://{username}:{password}@{host}:{port}/{database}‘ engine = create_engine(DB_URI) # 创建引擎Base = declarative_base(engine) # 使用declarative_base创建基类session = sessionmaker(engine)()
创建模型
class User(Base): __tablename__ = ‘user‘ id = Column(Integer, primary_key=True, autoincrement=True) username = Column(String(50), nullable=False) def __repr__(self): return f‘User(username: {self.username})‘ 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‘)) author = relationship(‘User‘, backref=‘article‘) def __repr__(self): return f‘Article(title: {self.title})‘ Base.metadata.drop_all() # 删除所有表Base.metadata.create_all() # 创建表
插入数据
user = User(username=‘aaa‘)article = Article(title=‘xxxxxxx‘)article.author = user session.add(article)session.commit()
写SQL删除user信息,报外键约束
使用sqlalchemy删除,成功
user = session.query(User).first()session.delete(user)session.commit()
可见,sqlalchemy删除时会将外键设置为null,所以为了使用外键约束,需在建表的时候,设置外键nullable=False,即不允许为空
class User(Base): __tablename__ = ‘user‘ id = Column(Integer, primary_key=True, autoincrement=True) username = Column(String(50), nullable=False) def __repr__(self): return f‘User(username: {self.username})‘ 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‘), nullable=False) author = relationship(‘User‘, backref=‘article‘) def __repr__(self): return f‘Article(title: {self.title})‘ Base.metadata.drop_all() # 删除所有表Base.metadata.create_all() # 创建表 user = User(username=‘aaa‘)article = Article(title=‘xxxxxxx‘)article.author = user session.add(article)session.commit()
再次删除,就会报错
user = session.query(User).first()session.delete(user)session.commit()
原文地址:https://www.cnblogs.com/zhongyehai/p/11816432.html
时间: 2024-07-30 01:21:49