#encoding: utf-8 from sqlalchemy import create_engine,Column,Integer,String,Float,func,and_,or_,Text,\
ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker,relationship
from random import randint 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) #父表/从表
#user/article 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 class Article(Base):
__tablename__ = 'article'
id = Column(Integer,primary_key=True,autoincrement=True)
title = Column(String(50),nullable=False)
content = Column(Text,nullable=False)
uid = Column(Integer,ForeignKey('user.id',ondelete='RESTRICT'))
author = relationship('User',backref='articles') #sqlalchemy orm提供的 # Base.metadata.drop_all()
#
# Base.metadata.create_all()
#
#
# #添加数据
# user = User(username = 'xiaowu')
# session.add(user)
# session.commit()
#
# article = Article(title = '圣墟',content = '吹牛逼死坑的小说,天天吹水逼',uid = 1)
# session.add(article)
# session.commit() #现在有个需求,我要查询article表中关联user表的数据,同过uid查询
'''
article = session.query(Article).first()
uid = article.uid
user = session.query(User).get(uid) #get根据主键会对一个对象或None
print(user)
'''
#上面写法也行,但是有没有更简便的呢?
# from sqlalchemy.orm import relationship
#sqlalchemy为我们提供了 relationship article = session.query(Article).first() #获取user对象
user = article.author
print(user)
#通过author这个字段就能直接查询出User所有关联的内容
author_name = user.username
print(author_name) #我现在又另一个需求,获取用户发布的文章,该怎么做,
#首先我们要明白用户跟文章的关系,是 一对 多关系 user = session.query(User).first() article= user.articles
print(article)#获取文章对象 ,[<__main__.Article object at 0x0000021D7BA2FC18>]是列表 #获取用户发布的文件title article_title = article[0].title
print(article_title) #这时候就有疑问呢,同样是用relationship,为什么获取对象的类型却不一样,
'''
User (主表)对 Aritcle(子表) relationship 获取 aritcle的对象是列表包裹着的
而 Aritcle(子表) 对 User(主表)relationship 获取 user 的对象 就是 内存对象
要理解这种做法,就要理解一对多关系,user(用户)可以发表多篇文章,而 article(文章)
只能有一个用户发布,所以获取article的对象是列表包裹着的
''' #现在有一个需求 能不能 简化 relationship ,在子表显示
#author = relationship('User',backref='articles')
'''
backref 就是反关联的意思,反向引用,
article 通过 author 这个关键字 正向引用 user表中的字段
user 通过 articles 反向引用 article表中的字段
'''