003-sqlalchemy-外键与relationship的关系

使用外键与relationship，可以完成两个张表的关联。

如下例，son表中father_id外键关联到father表中id.

通过在father表对象中添加son这个relationship。

就实现了从一个father对象查询的结果中读取到son对象中的内容。

同时也可以实现从son对象来读取father对象内容。

import sqlalchemy
from sqlalchemy import create_engine
from sqlalchemy import Column,String,Integer,ForeignKey
from sqlalchemy.orm import sessionmaker,relationship
from sqlalchemy.ext.declarative import declarative_base

engine = create_engine("mysql+pymysql://root:root123@192.168.10.241/oldboydb2?charset=utf8")

Base = declarative_base()

class Father(Base):
    __tablename__ = "father"

    id = Column(Integer,primary_key=True,autoincrement=True)
    name = Column(String(40),unique=True)
    age = Column(Integer)
    son = relationship('Son',backref="father")
    #son = relationship('Son')

class Son(Base):
    __tablename__ = 'son'

    id = Column(Integer,primary_key=True,autoincrement=True)
    name = Column(String(40),unique=True)
    age = Column(Integer)
    #father = relationship('Father')

    father_id = Column(Integer,ForeignKey('father.id'))

# Base.metadata.create_all(engine)

MySession = sessionmaker(bind=engine)
session = MySession()

ret = session.query(Father).filter_by(id=1).first()
print(ret.son[0].name) #多个结果[<__main__.Son object at 0x0000000003F192B0>,
# <__main__.Son object at 0x0000000003F19320>]
#需要循环取值

ret = session.query(Son).filter_by(id=1).first()
print(ret.father.name)#一个结果<__main__.Father object at 0x0000000003F196D8>
#直接取值