sqlalchemy一对一关系映射

Posted 2021-01-08 python成长中

#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,backref
from random import randint

HOSTNAME = ‘127.0.0.1‘

PORT = 3306

DATABASE = ‘first_sqlalchemy‘

USERNAME = ‘root‘

PASSWORD = ‘123456‘

#dialect+driver://username:[email protected]: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)

    # 一对一的情况，这里要设置下,uselist设置成false,关闭列表让一对多，变成一对一的关系

    # extend = relationship(‘UserExtend‘,uselist=False)
    # articles = relationship("Article") #获取用户发布所有文章


#把不常用到的数据，放到另一张表里，这里就用到一对一

class UserExtend(Base):
    __tablename__ = ‘user_extend‘
    id = Column(Integer, primary_key=True, autoincrement=True)
    school = Column(String(50))
    uid = Column(Integer,ForeignKey(‘user.id‘))
    #一对一的时候使用下面情况：
    user = relationship(‘User‘,backref=backref(‘extend‘,uselist=False))

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()


user = User(username=‘辰东‘)

article1 = Article(title = ‘圣墟‘,content=‘这都是些啥‘)
article2 = Article(title = ‘遮天‘,content=‘这又是啥‘)

# user.articles 是什么数据类型

print(user.articles,type(user.articles)) #sqlalchemy.orm.collections.InstrumentedList

from sqlalchemy.orm.collections import InstrumentedList

#InstrumentedList是
‘‘‘
class InstrumentedList(list):
    """An instrumented version of the built-in list."""
‘‘‘
# user.articles.append(article1)
# user.articles.append(article2)
#
# session.add(user)
# session.commit()

#怎么反向添加呢

# article1.author = user #通过子表的关联字段反向的绑定主表的主键（这个是比较常见的）
#
# article2.author = user
#
# session.add(article1)
# session.add(article2)
#
# session.commit()

#这里尝试一下一对一的关系
user = User(username=‘xiaowu‘)
extend_user = UserExtend(school=‘大渡口中学‘)
# extend_user_1 = UserExtend(school=‘大同中学‘)

user.extend = extend_user
# extend.append(extend_user_1)

session.add(user)
session.commit()