python 之sqlalchemy many to one

通过查询多个父亲，对应一个儿子

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
@author: zengchunyun
"""
from sqlalchemy import Column, Integer, String, Float, DateTime, ForeignKey
from sqlalchemy.orm import sessionmaker, relationship, backref
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine

Base = declarative_base()
engine = create_engine('mysql+pymysql://root:123@127.0.0.1:3306/day11',echo=True)



class Parent(Base):
    __tablename__ = 'parent'
    id = Column(Integer, primary_key=True)
    name = Column(String(64))
    child_id = Column(Integer, ForeignKey("child.id"))
    childr = relationship("Child")


class Child(Base):
    __tablename__ = 'child'
    id = Column(Integer, primary_key=True)
    name = Column(String(64))



Base.metadata.create_all(engine)

DBSession = sessionmaker()
DBSession.configure(bind=engine)
session = DBSession()  # 打开数据连接




ret = session.query(Parent).filter(Parent.name == 'zeng').one()
print(ret)
print(ret.childr.name)
ret = session.query(Parent).filter(Parent.name == 'chunyun').one()
print(ret)
print(ret.childr.name)

ret = session.query(Parent).filter(Parent.name == 'chun').one()
print(ret)
print(ret.childr.name)

many to one 第二式

class Parent(Base):
    __tablename__ = 'parent'
    id = Column(Integer, primary_key=True)
    name = Column(String(64))
    child_id = Column(Integer, ForeignKey("child.id"))
    childr = relationship("Child", back_populates="parents")


class Child(Base):
    __tablename__ = 'child'
    id = Column(Integer, primary_key=True)
    name = Column(String(64))
    parents = relationship("Parent", back_populates="childr")找到父亲

＃通过双向建立映射关系，能让父亲查到儿子，也能让儿子

many to one 终极版

class Parent(Base):
    __tablename__ = 'parent'
    id = Column(Integer, primary_key=True)
    name = Column(String(64))
    child_id = Column(Integer, ForeignKey("child.id"))
    childr = relationship("Child", backref="parents")  # 这段代码,变相的等于在Child类中添加了parents = relationship("Parent", back_populates="childr")


class Child(Base):
    __tablename__ = 'child'
    id = Column(Integer, primary_key=True)
    name = Column(String(64))