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 = ''

#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)
'''