python-- pymsql外键

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 pymsql 外键

本片是以上一篇pymsql操作MySQL的补充,主要演示pymysql的外键操作使用

 

一、一对一外键关联

1、示意图

2、一对一外键关联示例

2.1、创建表结构,插入数据

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

connect = create_engine("mysql+pymysql://root:123456@localhost:3306/test",
                        encoding="utf-8",
                        echo=False)  # 连接数据库,echo=True =>把所有的信息都打印出来


Base = declarative_base()  # 生成ORM基类


class Student(Base):  # 学生表
    __tablename__ = "student"
    id = Column(Integer, primary_key=True)
    name = Column(String(32), nullable=False)
    register_date = Column(DATE, nullable=False)

    def __repr__(self):
        return "<{0} name:{1}>".format(self.id, self.name)


class StudentRecord(Base):   # 学生学习记录表
    __tablename__ = "study_record"
    id = Column(Integer, primary_key=True)
    day = Column(Integer, nullable=False)
    status = Column(String(32), nullable=False)
    stu_id = Column(Integer, ForeignKey("student.id"))  # 关联外键
    #关联student表,然后我需要在study_record里通过student这个字段,就可以去查Student类里面所有的字段,
    # 反过来利用backref="my_study_record"中的my_study_record,在student表里通过my_study_record这个字段反查study_record类里面的所有字段,
    Student = relationship("Student", backref="my_study_record")

    def __repr__(self):
        return "<name:{0} day:{1} stu_id:{2}>".format(self.Student.name, self.day, self.stu_id)

Base.metadata.create_all(connect)  # 创建学生表和学生记录表,在第一次创建后注释


session_class = sessionmaker(connect)  # 创建与数据库的会话session class ,这里返回给session的是个class,不是实例
session = session_class()  # 生成session实例


#在两个表中插入数据
stu1 = Student(name="test", register_date="2017-05-30")
stu2 = Student(name="test2", register_date="2017-06-30")
record1 = StudentRecord(day=1, status="Y", stu_id=1)
record2 = StudentRecord(day=2, status="Y", stu_id=1)
session.add_all([record1, record2])
session.commit()

2.2、根据关联外键,查对应表中信息

stu_obj = session.query(Student).filter_by(name="test").first()
print(stu_obj.my_study_record)  # 在学生表里查学生对应的学习记录

record_obj = session.query(StudentRecord).first()
print(record_obj.Student.name)  # 在学生记录表里面查学习记录对应学生的名字



#输出
[<name:test day:1 stu_id:1>, <name:test day:2 stu_id:1>]

test

 

 

二、一对多外键关联

案例一创建的是:一对一的外键关系,现在是一对多的外键关系

1、一对多外键关联示例:

1.1、创建表结构

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

Base = declarative_base()  # orm基类


class Customer(Base):   # 消费者表
    __tablename__ = "customer"
    id = Column(Integer, primary_key=True)
    name = Column(String(64))
    #创建两个外键,都指向address.id
    billing_address_id = Column(Integer, ForeignKey("address.id"))
    shipping_address_id = Column(Integer, ForeignKey("address.id"))

    #因为有两个外键,需要通过foreign_keys=[外键字段]告诉sqlalchemy关联哪个外键了,不然就会报错
    billing_address = relationship("Address", foreign_keys=[billing_address_id])
    shipping_address = relationship("Address", foreign_keys=[shipping_address_id])


class Address(Base):   # 收货地址表
    __tablename__ = "address"
    id = Column(Integer, primary_key=True)
    street = Column(String(64))
    city = Column(String(64))
    state = Column(String(64))

    def __repr__(self):
        return self.state + "-" + self.city + "-" + self.street


connect = create_engine("mysql+pymysql://root:123456@localhost:3306/test",
                        encoding="utf-8",
                        echo=False)  # 连接数据库,echo=True =>把所有的信息都打印出来

Base.metadata.create_all(connect)  # 创建所有的表

1.2、插入数据(默认规则创建数据表结构在一个.py文件,增删查改等操作不与表结构.py文件在一起)

import many_foreign_key # 导出表结构创建模块
from sqlalchemy.orm import sessionmaker

#创建session与数据库会话类,生成session实例
session_class = sessionmaker(bind=many_foreign_key.connect)
session = session_class()
#创建address
address1 = many_foreign_key.Address(street="nanshanqu", city="shenzhen", state="guangdong")
address2 = many_foreign_key.Address(street="baoanqu", city="shenzhen", state="guangdong")
#创建consumers
c1 = many_foreign_key.Customer(name="test", billing_address=address1, shipping_address=address1)
c2 = many_foreign_key.Customer(name="test1", billing_address=address2, shipping_address=address1)
#添加session提交
session.add_all([address1, address2, c1, c2])
session.commit()

1.3、查询数据

import many_foreign_key
from sqlalchemy.orm import sessionmaker

obj = session.query(many_foreign_key.Customer).filter_by(name="test1").first()
print(obj.name, obj.billing_address, obj.shipping_address)

#输出
test1 guangdong-shenzhen-baoanqu guangdong-shenzhen-nanshanqu

 

 

三、多对多外键关联

通过数据库模拟设计“图书”与“作者”的关系的表结构,从而来演示多对多外键关联:

  1. 一本书可以有好几个作者一起出版
  2. 一个作者可以写好几本书

1、多对多外键关联示例:

1.1、创建表结构

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


Base = declarative_base()  # 创建orm基类

# 创建一张中间表,用于对book表和author表之前的多对多关联, 中间表建立后由ORM自动维护
book_m2m_author = Table("book_m2m_author", Base.metadata,
                        Column("id", Integer, primary_key=True),
                        Column(\'books_id\', Integer, ForeignKey("books.id")),
                        Column(\'authors_id\', Integer, ForeignKey("authors.id")))


class Book(Base):
    __tablename__ = "books"
    id = Column(Integer, primary_key=True)
    name = Column(String(64))
    pub_date = Column(DATE)

    #关联authors表和中间表book_m2m_author,即可通过books反查出Author表中的数据或者#通过authors反查出books表中的数据
    authors = relationship("Author", secondary=book_m2m_author, backref="books")

    def __repr__(self):
        return self.name


class Author(Base):
    __tablename__ = "authors"
    id = Column(Integer,primary_key=True)
    name = Column(String(32))

    def __repr__(self):
        return self.name

connect = create_engine("mysql+pymysql://root:123456@localhost:3306/test?charset=utf8",
                        echo=False)  # 连接数据库,echo=True =>把所有的信息都打印出来

Base.metadata.create_all(connect)  # 创建所有表

数据关联示意图:

1.2、插入数据

import m2m_foreign_key
from sqlalchemy.orm import sessionmaker

#创建session与数据库会话类,生成session实例
session_class = sessionmaker(bind=m2m_foreign_key.connect)
session = session_class()
#创建book信息
b1 = m2m_foreign_key.Book(name="Python", pub_date="2017-08-08")
b2 = m2m_foreign_key.Book(name="JAVA", pub_date="2017-10-08")
b3 = m2m_foreign_key.Book(name="C", pub_date="2017-11-08")
#创建author信息
a1 = m2m_foreign_key.Author(name="test")
a2 = m2m_foreign_key.Author(name="test1")
a3 = m2m_foreign_key.Author(name="test2")
#创建中间表信息
b1.authors = [a1, a3]
b2.authors = [a1, a2, a3]

session.add_all([b1, b2, b3, a1, a2, a3])

session.commit()

1.3、查询数据

import m2m_foreign_key
from sqlalchemy.orm import sessionmaker

#创建session与数据库会话类,生成session实例
session_class = sessionmaker(bind=m2m_foreign_key.connect)
session = session_class()


authors_obj = session.query(m2m_foreign_key.Author).filter_by(name="test").first()
print(authors_obj.books)  # 通过books反查出books表中的数据
book_obj = session.query(m2m_foreign_key.Book).filter(m2m_foreign_key.Book.id == 2).first()
print(book_obj.authors)  # 通过authors反查出authors表中的数据
#输出
[Python, JAVA]
[test, test1, test2]

1.4、删除数据

删除数据时不用管book_m2m_authors , sqlalchemy会自动帮你把对应的数据删除

import m2m_foreign_key
from sqlalchemy.orm import sessionmaker

#创建session与数据库会话类,生成session实例
session_class = sessionmaker(bind=m2m_foreign_key.connect)
session = session_class()


#通过书删除作者
author_obj = session.query(m2m_foreign_key.Author).filter_by(name="test1").first()
book_obj = session.query(m2m_foreign_key.Book).filter_by(name="JAVA").first()
book_obj.authors.remove(author_obj)  # 从一本书里删除一个作者
session.commit()

#删除作者,会把这个作者跟所有书的关联关系数据也自动删除
author_obj =session.query(m2m_foreign_key.Author).filter_by(name="test").first()
# print(author_obj.name , author_obj.books)
s.delete(author_obj)
s.commit()

 

 

注:处理中文

sqlalchemy设置编码字符集一定要在数据库访问的URL上增加charset=utf8,否则数据库的连接就不是utf8的编码格式

eng = create_engine(\'mysql://root:root@localhost:3306/test2?charset=utf8\',echo=True)

  

 

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