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  • sqlalchemy的join使用

    ——、先看mysql的join链接方法

    #encoding: utf-8
    
    from sqlalchemy import create_engine,Column,Integer,String,Float,func,and_,or_,Enum,
        ForeignKey,DateTime
    from sqlalchemy.ext.declarative import declarative_base
    from sqlalchemy.orm import sessionmaker,relationship
    from random import randint
    from datetime import datetime
    HOSTNAME = '127.0.0.1'
    
    PORT = 3306
    
    DATABASE = 'first_sqlalchemy'
    
    USERNAME = 'root'
    
    PASSWORD = '123456'
    
    #dialect+driver://username:password@host:port/database
    DB_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)
    
    
    class User(Base):
        __tablename__ = 'user'
        id = Column(Integer,primary_key=True,autoincrement=True)
        username = Column(String(32),nullable=False)
    
        # articles = relationship("Article") #获取用户发布所有文章
        def __repr__(self):
            return '<User:%s>'%self.username
    
    
    class Article(Base):
        __tablename__ = 'article'
        id = Column(Integer,primary_key=True,autoincrement=True)
        title = Column(String(50),nullable=False)
        create_time = Column(DateTime,default=datetime.now)
        uid = Column(Integer,ForeignKey('user.id',ondelete='RESTRICT'))
        author = relationship('User',backref='articles') #sqlalchemy orm提供的
    
        def __repr__(self):
            return '<Article:%s>'%self.title
    
    
    # Base.metadata.drop_all()
    #
    # Base.metadata.create_all()
    #
    # user1 = User(username='zhiliao')
    # user2 = User(username='ketang')
    #
    # for x in range(1):
    #     article = Article(title='title%s'%x)
    #     article.author = user1
    #     session.add(article)
    # session.commit()
    #
    #
    # for x in range(1,3):
    #     article = Article(title='title%s'%x)
    #     article.author = user2
    #     session.add(article)
    # session.commit()
    
    
    #找到所有的用户,根据文章的数量进行排序
    
    result = session.query(User.username,func.count(Article.id)).join(Article,User.id==Article.uid).
        group_by(User.id).order_by(func.count(Article.id).desc()).all()
    print(result)#[('ketang', 2), ('zhiliao', 1)]
    
    '''
    SELECT user.username AS user_username, count(article.id) AS count_1 
    FROM user INNER JOIN article ON user.id = article.uid GROUP BY user.id ORDER BY count(article.id)
    '''
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  • 原文地址:https://www.cnblogs.com/wuheng-123/p/9719812.html
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