sqlalchemy外键的一些东西

数据库：

联表查询：

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

engine = create_engine("mysql+pymysql://root:[email protected]/mysqltest")
Base = declarative_base()

class Student(Base):
    __tablename__ = ‘student‘
    id = Column(Integer, primary_key=True)
    name = Column(String(32))
    sex = Column(String(32))
    def __repr__(self):
        return "%s,%s,%s" %(self.id, self.name, self.sex)

class Study_record(Base):
    __tablename__ = ‘study_record‘
    id = Column(Integer, primary_key=True)
    day = Column(Integer)
    status = Column(String(32))
    stu_id = Column(Integer)
    def __repr__(self):
        return "%s,%s,%s" %(self.day, self.status, self.stu_id)

Session_class = sessionmaker(bind=engine)
session = Session_class()

# select a.*,b.* from a,b where a.id=b.s_id
result = session.query(Student, Study_record).filter(Student.id==Study_record.stu_id).all()
print(result)  # [(1,alex,男, 1,YES,1), (1,alex,男, 2,NO,1), (2,jack,男, 1,YES,2), (2,jack,男, 2,YES,2)]
# 此处报错！！有外键关联的时候才能用，而且外键也需要用类映射出来。真TM麻烦！
result1 = session.query(Student).join(Study_record).all()
print(result1)

外键关联之双向反查：

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

engine = create_engine("mysql+pymysql://root:[email protected]/mysqltest")
Base = declarative_base()

#   学员表student跟考勤表study_record是一对多的关系
class Student(Base):
    __tablename__ = ‘student‘
    id = Column(Integer, primary_key=True)
    name = Column(String(32))
    sex = Column(String(32))
    def __repr__(self):
        return "%s,%s,%s" %(self.id, self.name, self.sex)

class Study_record(Base):
    __tablename__ = ‘study_record‘
    id = Column(Integer, primary_key=True)
    day = Column(Integer)
    status = Column(String(32))
    stu_id = Column(Integer, ForeignKey(‘student.id‘))
    # 双向反查关系，通过student字段可以看记录对应的学生，反过来通过my_study_record可看学生对应的记录
    student = relationship("Student", backref="my_study_record")
    def __repr__(self):   # self.student.name  这是它的牛逼之处：
        return "%s,%s,%s" %(self.day, self.status, self.student.name)

Session_class = sessionmaker(bind=engine)
session = Session_class()

# 上面加了外键关联，可以用了
result1 = session.query(Student).join(Study_record, isouter=True).all()
print(result1)  # [1,alex,男, 2,jack,男, 3,rose,女]

alex = session.query(Student).filter(Student.name == ‘alex‘).first()
print(alex)  # 1,alex,男
# 如果想查Alex的上课记录咋查呢？在上面加一个双向反查关系
print(alex.my_study_record)  # [1,YES,alex, 2,NO,alex]

顾客表有两个外键，两个外键指向同一张表，此时的双向查询：

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

engine = create_engine("mysql+pymysql://root:[email protected]/mysqltest")
Base = declarative_base()

# 顾客表Customer有两个外键，订单地址ID，邮寄地址ID。都关联了同一张表
class Customer(Base):
    __tablename__ = ‘customer‘
    id = Column(Integer, primary_key=True)
    name = Column(String(32))

    bill_addr_id = Column(Integer, ForeignKey("address.id"))
    post_addr_id = Column(Integer, ForeignKey("address.id"))

    bill_addr = relationship("Address", foreign_keys=[bill_addr_id], backref="bill_customers")
    post_addr = relationship("Address", foreign_keys=[post_addr_id], backref="post_customers")

    def __repr__(self):
        return "%s" %(self.name)

class Address(Base):
    __tablename__ = ‘address‘
    id = Column(Integer, primary_key=True)
    detail_address = Column(String(32))
    def __repr__(self):
        return "%s" %(self.detail_address)

Base.metadata.create_all(engine)

orms模块

from sqlalchemy.orm import sessionmaker
import orms

Session_class = sessionmaker(bind=orms.engine)
session = Session_class()
a1 = orms.Address(detail_address="BeiJing")
a2 = orms.Address(detail_address="ShangHai")
a3 = orms.Address(detail_address="TianJin")

session.add_all([a1, a2, a3])
# 注意这里赋值的牛逼之处！！！直接用对象进行赋值
c1 = orms.Customer(name="Alex", bill_addr=a1, post_addr=a2)
c2 = orms.Customer(name="Jack", bill_addr=a2, post_addr=a3)
c3 = orms.Customer(name="Rain", bill_addr=a3, post_addr=a3)

session.add_all([c1, c2, c3])
session.commit()

init_data模块

from sqlalchemy.orm import sessionmaker
import orms

Session_class = sessionmaker(bind=orms.engine)
session = Session_class()

alex = session.query(orms.Customer).filter(orms.Customer.name=="Alex").first()
print(alex.bill_addr, alex.post_addr)  # BeiJing ShangHai

sh = session.query(orms.Address).filter(orms.Address.detail_address=="ShangHai").first()
print(sh.bill_customers)  # [Jack]

原文地址：https://www.cnblogs.com/staff/p/9998761.html