【Python之路】第十九篇--Python操作MySQL

2023-07-31 14:34:34

本篇对于Python操作MySQL主要使用两种方式：

原生模块 pymsql
ORM框架 SQLAchemy

pymsql

pymsql是Python中操作MySQL的模块，其使用方法和MySQLdb几乎相同。

下载安装

pip3 install pymysql

使用操作

1、执行SQL

# 创建连接

conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='123456', db='db1',charset='utf8')

# 创建游标

cursor = conn.cursor()

# 执行SQL，并返回受影响行数

effect_row = cursor.execute("update hosts set host = '1.1.1.2' where nid > %s", (1,))

# 执行SQL，并返回受影响行数

effect_row = cursor.executemany("insert into hosts(host,color_id)values(%s,%s)", [("1.1.1.11",1),("1.1.1.11",2)])

# 提交，不然无法保存新建或者修改的数据

conn.commit()

# 关闭游标

cursor.close()

# 关闭连接

conn.close()

增,删,改需要执行 conn.commit()

2、获取新创建数据自增ID

import pymysql

conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='123', db='t1')

cursor = conn.cursor()

cursor.executemany("insert into hosts(host,color_id)values(%s,%s)", [("1.1.1.11",1),("1.1.1.11",2)])

conn.commit()

cursor.close()

conn.close()

# 获取最新自增ID  => 如果插入多条,只能拿到最后一条id

new_id = cursor.lastrowid

3、获取查询数据

import pymysql

conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='123', db='t1')

cursor = conn.cursor()

cursor.execute("select * from hosts")

# 获取第一行数据

row_1 = cursor.fetchone()

# => 再次执行:cursor.fetchone() 获得下一条数据,没有时为None

# 获取前n行数据

# row_2 = cursor.fetchmany(n)

# ==> 执行了n次fetchone()

# 获取所有数据

# row_3 = cursor.fetchall()

conn.commit()

cursor.close()

conn.close()

注：在fetch数据时按照顺序进行，可以使用cursor.scroll(num,mode)来移动游标位置，如：

cursor.scroll(-1,mode='relative') # 相对当前位置移动
cursor.scroll(2,mode='absolute') # 相对绝对位置移动

4、fetch数据类型

　　关于默认获取的数据是元祖类型，如果想要或者字典类型的数据，即：

import pymysql

conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='123456', db='t1')

# 游标设置为字典类型

cursor = conn.cursor(cursor=pymysql.cursors.DictCursor)

row = cursor.execute("select * from user")

result = cursor.fetchone()

print(result)

conn.commit()

cursor.close()

conn.close()

补充:

1.SQL注入

由于字符串拼接出现注入

"select name from user where name='%s' and password ='%s' " %(username,password)

pymysql 提供了转义功能:

"select name from user where name=%s and password =%s ",( username,password )

SQLAchemy

SQLAlchemy是Python编程语言下的一款ORM框架，该框架建立在数据库API之上，使用关系对象映射进行数据库操作，

简言之便是：将对象转换成SQL，然后使用数据API执行SQL并获取执行结果。

ORM:

ORM框架的作用就是把数据库表的一行记录与一个对象互相做自动转换。正确使用ORM的前提是了解关系数据库的原理。

ORM就是把数据库表的行与相应的对象建立关联，互相转换。由于关系数据库的多个表还可以用外键实现一对多、多对多等关联，

相应地， ORM框架也可以提供两个对象之间的一对多、多对多等功能。

SQLAlchemy:

本身无法操作数据库，其必须以pymsql等第三方插件，

Dialect用于和数据API进行交流，根据配置文件的不同调用不同的数据库API，从而实现对数据库的操作，如：

MySQL-Python

    mysql+mysqldb://<user>:<password>@<host>[:<port>]/<dbname>

pymysql

    mysql+pymysql://<username>:<password>@<host>/<dbname>[?<options>]

MySQL-Connector

    mysql+mysqlconnector://<user>:<password>@<host>[:<port>]/<dbname>

cx_Oracle

    oracle+cx_oracle://user:pass@host:port/dbname[?key=value&key=value...]

更多详见：http://docs.sqlalchemy.org/en/latest/dialects/index.html

#!/usr/bin/env python

# -*-coding:utf-8 -*-

from sqlalchemy import create_engine,and_,or_,func,Table

from sqlalchemy.ext.declarative import declarative_base

from sqlalchemy import Column, Integer, String,ForeignKey

from  sqlalchemy.orm import sessionmaker,relationship

engine = create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/t1?charset=utf8", max_overflow=5)

Base = declarative_base()

def init_db():

    Base.metadata.create_all(engine)   

def drop_db():

    Base.metadata.drop_all(engine)

一、底层处理

使用 Engine/ConnectionPooling/Dialect 进行数据库操作，Engine使用ConnectionPooling连接数据库，然后再通过Dialect执行SQL语句。

#!/usr/bin/env python

# -*- coding:utf-8 -*-

from sqlalchemy import create_engine

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=5)

# 执行SQL

# cur = engine.execute(

#     "INSERT INTO hosts (host, color_id) VALUES ('1.1.1.22', 3)"

# )

# 新插入行自增ID

# cur.lastrowid

# 执行SQL

# cur = engine.execute(

#     "INSERT INTO hosts (host, color_id) VALUES(%s, %s)",[('1.1.1.22', 3),('1.1.1.221', 3),]

# )

# 执行SQL

# cur = engine.execute(

#     "INSERT INTO hosts (host, color_id) VALUES (%(host)s, %(color_id)s)",

#     host='1.1.1.99', color_id=3

# )

# 执行SQL

# cur = engine.execute('select * from hosts')

# 获取第一行数据

# cur.fetchone()

# 获取第n行数据

# cur.fetchmany(3)

# 获取所有数据

# cur.fetchall()

二、ORM功能使用

使用 ORM/Schema Type/SQL Expression Language/Engine/ConnectionPooling/Dialect 所有组件对数据进行操作。

根据类创建对象，对象转换成SQL，执行SQL。处理中文数据时,在连接数据库时要加上 ?charset=utf8

1.创建表

#!/usr/bin/env python

# -*- coding:utf-8 -*-

from sqlalchemy.ext.declarative import declarative_base

from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index

from sqlalchemy.orm import sessionmaker, relationship

from sqlalchemy import create_engine

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=5)

Base = declarative_base()

# 创建单表

class Users(Base):

    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)

    name = Column(String(32))

    extra = Column(String(16))

    # 设置索引:

    __table_args__ = (

    UniqueConstraint('id', 'name', name='uix_id_name'),

        Index('ix_id_name', 'name', 'extra'),

    )

    # 输出Users对象时,调用:

    def __repr__(self):

        return "%s-%s-%s" % (self.id, self.name , self.extra)

def init_db():

    Base.metadata.create_all(engine)   #创建表 

def drop_db():

    Base.metadata.drop_all(engine)    #删除表

一对多

# 一对多

class Favor(Base):

    __tablename__ = 'favor'

    nid = Column(Integer, primary_key=True)

    caption = Column(String(50), default='red', unique=True)

class Person(Base):

    __tablename__ = 'person'

    nid = Column(Integer, primary_key=True)

    name = Column(String(32), index=True, nullable=True)

    favor_id = Column(Integer, ForeignKey("favor.nid"))   # 外键

多对多

# 多对多

class Group(Base):

    __tablename__ = 'group'

    id = Column(Integer, primary_key=True)

    name = Column(String(64), unique=True, nullable=False)

    port = Column(Integer, default=22)

class Server(Base):

    __tablename__ = 'server'

    id = Column(Integer, primary_key=True, autoincrement=True)

    hostname = Column(String(64), unique=True, nullable=False)

class ServerToGroup(Base):

    __tablename__ = 'servertogroup'

    nid = Column(Integer, primary_key=True, autoincrement=True)

    server_id = Column(Integer, ForeignKey('server.id'))

    group_id = Column(Integer, ForeignKey('group.id'))

2.操作表

#!/usr/bin/env python

# -*- coding:utf-8 -*-

from sqlalchemy.ext.declarative import declarative_base

from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index

from sqlalchemy.orm import sessionmaker, relationship

from sqlalchemy import create_engine

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=5)

#生成一个SQLORM基类

Base = declarative_base()

# 创建单表

class Users(Base):

    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)

    name = Column(String(32))

    extra = Column(String(16))

    __table_args__ = (

    UniqueConstraint('id', 'name', name='uix_id_name'),

        Index('ix_id_name', 'name', 'extra'),

    )

    def __repr__(self):

        return "%s-%s" %(self.id, self.name)

# 一对多

class Favor(Base):

    __tablename__ = 'favor'

    nid = Column(Integer, primary_key=True)

    caption = Column(String(50), default='red', unique=True)

    def __repr__(self):

        return "%s-%s" %(self.nid, self.caption)

class Person(Base):

    __tablename__ = 'person'

    nid = Column(Integer, primary_key=True)

    name = Column(String(32), index=True, nullable=True)

    favor_id = Column(Integer, ForeignKey("favor.nid"))

    # 与生成表结构无关，仅用于查询方便

    favor = relationship("Favor", backref='pers')

# 多对多

class ServerToGroup(Base):

    __tablename__ = 'servertogroup'

    nid = Column(Integer, primary_key=True, autoincrement=True)

    server_id = Column(Integer, ForeignKey('server.id'))

    group_id = Column(Integer, ForeignKey('group.id'))

    group = relationship("Group", backref='s2g')

    server = relationship("Server", backref='s2g')

class Group(Base):

    __tablename__ = 'group'

    id = Column(Integer, primary_key=True)

    name = Column(String(64), unique=True, nullable=False)

    port = Column(Integer, default=22)

    # group = relationship('Group',secondary=ServerToGroup,backref='host_list')

class Server(Base):

    __tablename__ = 'server'

    id = Column(Integer, primary_key=True, autoincrement=True)

    hostname = Column(String(64), unique=True, nullable=False)

def init_db():

    Base.metadata.create_all(engine)

def drop_db():

    Base.metadata.drop_all(engine)

# 这两行触发sessionmaker类下的__call__方法，return得到 Session实例，赋给变量session，

# 所以session可以调用Session类下的add，add_all等方法

Session = sessionmaker(bind=engine)

session = Session()

.增

obj = Users(name="alex0", extra='sb')

session.add(obj)

session.add_all([

    Users(name="alex1", extra='sb'),

    Users(name="alex2", extra='sb'),

])

session.commit()

.删

session.query(Users).filter(Users.id > 2).delete()

session.commit()

.改

session.query(Users).filter(Users.id > 2).update({"name" : ""})

session.query(Users).filter(Users.id > 2).update({Users.name: Users.name + ""}, synchronize_session=False)

session.query(Users).filter(Users.id > 2).update({"num": Users.num + 1}, synchronize_session="evaluate")

session.commit()

.查

ret = session.query(Users).all()

ret = session.query(Users.name, Users.extra).all()

ret = session.query(Users).filter_by(name='alex').all()

ret = session.query(Users).filter_by(name='alex').first()

3.更多查询方法:

#!/usr/bin/env python

# -*-coding:utf-8 -*-

from sqlalchemy import create_engine,and_,or_,func,Table

from sqlalchemy.ext.declarative import declarative_base

from sqlalchemy import Column, Integer, String,ForeignKey

from  sqlalchemy.orm import sessionmaker,relationship

engine = create_engine('mysql+pymysql://root@127.0.0.1:3307/day40?charset=utf8')

Base = declarative_base()

class Man_To_Woman(Base):

    __tablename__ = 'man_to_woman'

    nid = Column(Integer,primary_key=True)

    man_id = Column(Integer,ForeignKey('man.nid'))

    woman_id = Column(Integer,ForeignKey('woman.nid'))

class Man(Base):

    __tablename__ = 'man'

    nid = Column(Integer,primary_key=True)

    name = Column(String(20),nullable=False)

    woman = relationship("Woman", secondary=Man_To_Woman.__table__)

class Woman(Base):

    __tablename__ = 'woman'

    nid = Column(Integer,primary_key=True)

    name = Column(String(20),nullable=False)

    man = relationship("Man",secondary=Man_To_Woman.__table__)

Base.metadata.create_all(engine)

MySession = sessionmaker(engine)

session = MySession()

事例: 表结构

1.filter_by( ... ) 填写键值对方式

ret = session.query(Man).filter_by(name='alex').first()

print(ret.nid,ret.name)

2.filter 填写条件判断

ret = session.query(Man).filter(Man.name=='eric').first()

ret = session.query(Man).filter(Man.name=='eric' , Man.nid > 0).first()

row = session.query(Man).filter(Man.nid.between(1,4)).all()

ret = session.query(Users).filter(Users.id.in_(session.query(Users.id).filter_by(name='eric'))).all()

3.and_ or_ 条件判断

from sqlalchemy import and_, or_

ret = session.query(Man).filter(and_(Man.name == 'eric',Man.nid == 2)).first()

ret = session.query(Man).filter(or_(Man.name == 'eric',Man.nid == 2)).first()

4.~ 取反

ret = session.query(Man).filter(Man.nid.in_([2,3])).first()

ret = session.query(Man).filter(~Man.nid.in_([2,3])).first()

5.like + % 通配符

ret = session.query(Man).filter(Man.name.like('%x')).first()

ret = session.query(Man).filter(~Man.name.like('%x')).first()

6.切片限制 ( 序号,前闭后开 )

row = session.query(Man)[1:3]

for ret in row:

    print(ret.nid, ret.name)

row = session.query(Man).limit(3).offset(1)

7.order_by 排序

row = session.query(Man).order_by(Man.nid.desc()).all()

row = session.query(Man).order_by(Man.nid.asc()).all()

8.group_by 分组

row = session.query(func.count('*')).select_from(Man).all()

row = session.query(func.count('*')).filter(Man_To_Woman.nid > 1).all()

row = session.query(func.count('*')).select_from(Man_To_Woman).group_by(Man_To_Woman.man_id).all()

row = session.query(func.count('*')).select_from(Man_To_Woman).group_by(Man_To_Woman.man_id).limit(1).all()

row = session.query(Man_To_Woman).group_by(Man_To_Woman.man_id).all()

ret = session.query(Users).group_by(Users.extra).all()

ret = session.query(

    func.max(Users.id),

    func.sum(Users.id),

    func.min(Users.id)).group_by(Users.name).all()

ret = session.query(

    func.max(Users.id),

    func.sum(Users.id),

    func.min(Users.id)).group_by(Users.name).having(func.min(Users.id) >2).all()

9.join 连表

row = session.query(Users, Favor).filter(Users.id == Favor.nid).all()

ret = session.query(Son).join(Father).all()

ret = session.query(Son).join(Father, isouter=True).all()

10.union 组合

q1 = session.query(Users.name).filter(Users.id > 2)

q2 = session.query(Favor.caption).filter(Favor.nid < 2)

ret = q1.union(q2).all()

q1 = session.query(Users.name).filter(Users.id > 2)

q2 = session.query(Favor.caption).filter(Favor.nid < 2)

ret = q1.union_all(q2).all()

更多功能参见文档，猛击这里下载PDF

补充 Relationship:

改变数据输出的方式:可以在表的类中定义一个特殊成员:__repr__, return一个自定义的由字符串拼接的数据连接方式.
数据库中表关系之间除了MySQL中标准的外键(ForeignKey)之外,还可以创建一个虚拟的关系,比如 group = relationship("Group",backref='uuu'),一般此虚拟关系与foreignkey一起使用.

relationship : 通过relatioinship 找到绑定关系的数据 !!!

一对多,连表操作:

class Father(Base):

    __tablename__ ='father'

    nid = Column(Integer,primary_key=True)

    name = Column(String(32))

    son = relationship('Son')

class Son(Base):

    __tablename__ = 'son'

    nid = Column(Integer, primary_key=True)

    name = Column(String(32))

    father_id = Column(Integer,ForeignKey('father.nid'))

    father = relationship('Father')

表结构

正向查询:

需求:查询Son表中所有数据,并且显示对应的Father表中的数据.

ret = session.query(Son).all()

for obj in ret:

    print(obj.nid,obj.name,obj.father_id,obj.father.name)

反向查询:

需求:查询Father表中, 属于 alvin 的所有儿子Son.

obj = session.query(Father).filter(Father.name=='alvin').first()

row = obj.son

for ret in row:

    print(ret.nid,ret.name,ret.father.name)

多对多,连表操作:

#!/usr/bin/env python

# -*-coding:utf-8 -*-

from sqlalchemy import create_engine,and_,or_,func,Table

from sqlalchemy.ext.declarative import declarative_base

from sqlalchemy import Column, Integer, String,ForeignKey

from  sqlalchemy.orm import sessionmaker,relationship

engine = create_engine('mysql+pymysql://root@127.0.0.1:3307/day40?charset=utf8')

Base = declarative_base()

class Man_To_Woman(Base):

    __tablename__ = 'man_to_woman'

    nid = Column(Integer,primary_key=True)

    man_id = Column(Integer,ForeignKey('man.nid'))

    woman_id = Column(Integer,ForeignKey('woman.nid'))

class Man(Base):

    __tablename__ = 'man'

    nid = Column(Integer,primary_key=True)

    name = Column(String(20),nullable=False)

    woman = relationship("Woman", secondary=Man_To_Woman.__table__)

class Woman(Base):

    __tablename__ = 'woman'

    nid = Column(Integer,primary_key=True)

    name = Column(String(20),nullable=False)

    man = relationship("Man",secondary=Man_To_Woman.__table__)

Base.metadata.create_all(engine)

MySession = sessionmaker(engine)

session = MySession()

表结构

正,反向操作:

1.alex的所有女人

2.凤姐的所有男人

man1 = session.query(Man).filter(Man.name=='alex').first()

print(man1)

for ret in man1.woman:

    print(ret.nid,ret.name)

woman1 = session.query(Woman).filter(Woman.name=='fengjie').first()

print(woman1)

for ret in woman1.man:

    print(ret.nid,ret.name)

relatioinship 语句的简写: ,我添加到Man表中

woman = relationship("Woman", secondary=Man_To_Woman.__table__,backref='man')

1 关于 session.add session.query session.commit的顺序问题？

在同一个会话中， insert into table (xxxx)后，可以接着 select * from xxx; 查询到刚刚插入的数据；

只是不能在其他会话，比如我另开一个客户端去连接数据库不能查询到刚刚插入的数据。

这个数据已经到数据库。值是数据库吧这个数据给锁了。只有插入数据的那个session可以查看到，其他的session不能查看到，可以理解提交并解锁吧。

码农公寓

pymsql

SQLAchemy

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