三种排序方式

#encoding: utf-8

from sqlalchemy import create_engine,Column,Integer,String,Float,func,and_,or_,Text,
    ForeignKey,DateTime
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker,relationship,backref
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)

#第三种排序方式根据一对多，多对对关系，进行排序，排序只能作用在多的关系上，


class User(Base):
    __tablename__ = 'user'
    id = Column(Integer, primary_key=True, autoincrement=True)
    username = Column(String(50),nullable=False)

class Article(Base):
    __tablename__ = 'article'
    id = Column(Integer,primary_key=True,autoincrement=True)
    title = Column(String(50),nullable=False)
    create_time = Column(DateTime,nullable=False,default=datetime.now)#datetime.now不能加括号，是文章生成插入数据库的时间
    uid = Column(Integer,ForeignKey('user.id'))
    #第三种排序方式，跟relationship结合使用，作用多的关系上
    author = relationship("User",back_ref=backref('articles',order_by=create_time.desc()))
    #第二种排序方式，使用魔术属性
    __mapper_args__ = {
        "order_by": create_time.desc()
    }

    def __repr__(self):
        return '<article:{0},create_time:{1}>'.format(self.title,self.create_time)
# Base.metadata.drop_all()
# Base.metadata.create_all()

# article = Article(title='123456')
# session.add(article)
# session.commit()

#一个order_by根据文章的发表时间进行查询
#字段前没有减号（-）就是升序排列
#字段前有减号（-）就是降序排列
# article = session.query(Article).order_by(-Article.create_time).all()
#或使用desc，来倒序
# article = session.query(Article).order_by(-Article.create_time.desc).all()
#或用字段名来倒叙
# article = session.query(Article).order_by("-create_time").all()
# print(article)
"""
SELECT article.id AS article_id, article.title AS article_title,
article.create_time AS article_create_time 
FROM article ORDER BY article.create_time
"""

#使用第二种排序方式试一试
articles = session.query(Article).all()
print(articles)#测试是可以的