Python sqlalchemy orm 多外键关联

 多外键关联

注：在两个表之间进行多外键链接

如图：

案例：

# 创建两张表并添加外键主键

# 调用Column创建字段 加类型
from sqlalchemy import Integer, ForeignKey, String, Column

# 调用基类Base
from sqlalchemy.ext.declarative import declarative_base

# 调用操作链接,反查
from sqlalchemy.orm import relationship

# 调用链接数据库
from sqlalchemy import create_engine

Base = declarative_base()

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

    # 以Address表id字段 设置两个外键
    billing_address_id = Column(Integer, ForeignKey("address.id"))
    shipping_address_id = Column(Integer, ForeignKey("address.id"))

    # relationship -允许你在Student表里通过backref字段反向查出所有它在表里的关联项-
    # foreign_keys=绑定外键 多次relationship 反差会识别不出指定数据所以添加foreign_keys参数。
    billing_address = relationship("Address",foreign_keys=[billing_address_id])
    shipping_address = relationship("Address",foreign_keys=[shipping_address_id])

class Address(Base):
    __tablename__ = 'address'
    id = Column(Integer, primary_key=True)
    street = Column(String(64))
    city = Column(String(64))
    state = Column(String(64))

    # 返回一个可以用来表示对象的可打印字符串
    def __repr__(self):
        return self.street


# encoding='utf-8' 链接字符集 ，echo=True 把所有信息打印出来
engine = create_engine("mysql+pymysql://root:123456@192.168.1.100/xiang",encoding='utf-8',
                       #echo=True
                       )

#---------------1.创建表-----------------#
# 创建表结构
Base.metadata.create_all(engine)
#---------------------------------------#

# 插入表内字段数据，测试访问

from www import orm_fk
from sqlalchemy.orm import sessionmaker

# bind=engine 绑定engine socket实例
Session_class = sessionmaker(bind=orm_fk.engine)

# 生成session实例，如同pymysql内的cursor
Session = Session_class()


#---------------2.写入数据-----------------#

# 写入数据
# addr1 = orm_fk.Address(street="Tiantongyuan",city="ChangPing",state="BJ")
# addr2 = orm_fk.Address(street="Wudaokou",city="Haidian",state="BJ")
# addr3 = orm_fk.Address(street="Yanjiao",city="Langfang",state="HB")

# 插入数据
# Session.add_all([addr1,addr2,addr3])

# 写入数据 并调用 Address字段插入数据 为 Customer数据
# c1 = orm_fk.Customer(name="kevin",billing_address=addr1,shipping_address=addr2)
# c2 = orm_fk.Customer(name="Jack",billing_address=addr3,shipping_address=addr3)

# 插入数据
# Session.add_all([c1,c2])
#---------------------------------------#


#---------------3.查询数据-----------------#

# 取出Customer内的 内存对象
obj = Session.query(orm_fk.Customer).filter(orm_fk.Customer.name=="kevin").first()

# 通过内存 调用第一行name字段数据，
# 调用billing_address对应外键id的对应数据，
# 调用obj.shipping_address对应外键id的对应数据。
print(obj.name,obj.billing_address,obj.shipping_address)
#---------------------------------------#


# 执行事务
Session.commit()

# 表customer
+----+-------+--------------------+---------------------+
| id | name  | billing_address_id | shipping_address_id |
+----+-------+--------------------+---------------------+
|  1 | kevin |                  1 |                   2 |
|  2 | Jack  |                  3 |                   3 |
+----+-------+--------------------+---------------------+

# 表address
+----+--------------+-----------+-------+
| id | street       | city      | state |
+----+--------------+-----------+-------+
|  1 | Tiantongyuan | ChangPing | BJ    |
|  2 | Wudaokou     | Haidian   | BJ    |
|  3 | Yanjiao      | Langfang  | HB    |
+----+--------------+-----------+-------+