orm可以将数据库存储的数据封装成对象，同时，如果封装的好的话，所有的数据库操作都可以封装到对象中。这样的代码在组织结构上会非常的清晰，并且相对与使用sql语句在sql注入方面会极具降低。

SQLAlchemy中的映射关系有四种，分别是一对多，多对一，一对一，多对多

实现这种映射关系只需要外键(ForeignKey),和relationship

 

一对多：

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, CHAR
from sqlalchemy import ForeignKey
from sqlalchemy.orm import relationship, backref

Base = declarative_base()

class Parent(Base):
    __table__ = "parent"
    id = Column(Integer, Primary_key=True)
    name = Column(CHAR(50))
    child = relationship("child", backref="parent")

class Child(Base):
    __table__ = "child"
    id = Column(Integer, Primary_key=True)
    name = Column(CHAR(50))
    parent_id = Column(Integer,ForeignKey('parent.id'))

 

多对一：（建议）

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, CHAR
from sqlalchemy import ForeignKey
from sqlalchemy.orm import relationship, backref

Base = declarative_base()

class Parent(Base):
    __table__ = "parent"
    id = Column(Integer, Primary_key=True)
    name = Column(CHAR(50))

class Child(Base):
    __table__ = "child"
    id = Column(Integer, Primary_key=True)
    name = Column(CHAR(50))
    parent_id = Column(Integer,ForeignKey('parent.id'))
    parent = relationship("parent", backref="child")