#encoding: utf-8from sqlalchemy import create_engine,Column,Integer,String,Float,func,and_,or_,Text,\    ForeignKey,Tablefrom sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy.orm import sessionmaker,relationship,backreffrom random import randintHOSTNAME = '127.0.0.1'PORT = 3306DATABASE = 'first_sqlalchemy'USERNAME = 'root'PASSWORD = '123456'#dialect+driver://username:password@host:port/databaseDB_URI = "mysql+pymysql://{username}:{password}@{host}:{port}/" \         "{db}?charset=utf8".format(username=USERNAME,password=PASSWORD,host=HOSTNAME,port=PORT,db=DATABASE)engine = create_engine(DB_URI)Base = declarative_base(engine)# Session = sessionmaker(engine)# session = Session()session = sessionmaker(engine)() #Session(**local_kw)#使用Table这个类来实现多对多关系的第三张表article_tag = Table(    'article_tag',#第三张表名    Base.metadata, #元类的数据    Column('article_id',Integer,ForeignKey('article.id'),primary_key=True),#关联文章的字段    Column('tag_id',Integer,ForeignKey('tag.id'),primary_key=True),#标签的外键关联字段    #两字段primary_key都等于True，组合主键唯一，防止内容一样)class Article(Base):    __tablename__ = 'article'    id = Column(Integer,primary_key=True,autoincrement=True)    title = Column(String(50),nullable=False)    #反向关联，Tag关联的表，Article同tags关联Tag，Tag通过articles反向关联，    #secondary就是第三张表    tags = relationship('Tag',backref='articles',secondary=article_tag)class Tag(Base):    __tablename__ = 'tag'    id = Column(Integer, primary_key=True, autoincrement=True)    name = Column(String(50),nullable=False)# Base.metadata.drop_all()## Base.metadata.create_all()#多对多关系，所获取得对象都是，外层列表包裹着对象，记住只要是多得关系都是#列表包裹着对象# article1 = Article(title='武动乾坤')# article2 = Article(title='斗破苍穹')## tag1 = Tag(name='玄幻')# tag2 = Tag(name='YY小说')## article1.tags.append(tag1)# article1.tags.append(tag2)## session.add(article1)# session.add(article2)## session.commit()#多对多的查tag1 = session.query(Tag).filter(Tag.name == 'YY小说').all()print(tag1) #用all（)方法都是列表，first（）方法都是单个的对象print(tag1[0].articles)