MySQL（Python+ORM）

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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

1	`pip3 install pymysql`

使用操作

1、执行SQL

#!/usr/bin/env python

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

import pymysql

# 创建连接

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

# 创建游标

cursor = conn.cursor()

# 执行SQL，并返回收影响行数

effect_row = cursor.execute("update hosts set host = '1.1.1.2'")

# 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()

2、获取新创建数据自增ID

#!/usr/bin/env python

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

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

new_id = cursor.lastrowid

3、获取查询数据

#!/usr/bin/env python

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

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()

# 获取前n行数据

# row_2 = cursor.fetchmany(3)

# 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：

#!/usr/bin/env python

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

import pymysql

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

# 游标设置为字典类型

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

r = cursor.execute("call p1()")

result = cursor.fetchone()

conn.commit()

cursor.close()

conn.close()

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。

安装：

1	`pip3 install SQLAlchemy`

SQLAlchemy本身无法操作数据库，其必须以来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

一、内部处理

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。

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))

__table_args__ = (

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

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

)

# 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"))

# 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'))

def init_db():

Base.metadata.create_all(engine)

def drop_db():

Base.metadata.drop_all(engine)

注：设置外检的另一种方式 ForeignKeyConstraint(['other_id'], ['othertable.other_id'])

2、操作表

#!/usr/bin/env python
# -*- coding:utf- -*-
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_engineengine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=)Base = declarative_base()# 创建单表
class Users(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String())
extra = Column(String()) __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(), 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(), 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(), unique=True, nullable=False)
port = Column(Integer, default=)
# group = relationship('Group',secondary=ServerToGroup,backref='host_list')class Server(Base):
__tablename__ = 'server' id = Column(Integer, primary_key=True, autoincrement=True)
hostname = Column(String(), unique=True, nullable=False)def init_db():
Base.metadata.create_all(engine)def drop_db():
Base.metadata.drop_all(engine)Session = sessionmaker(bind=engine)
session = Session()

表结构 + 数据库连接

obj = Users(name="alex0", extra='sb')
session.add(obj)
session.add_all([
Users(name="alex1", extra='sb'),
Users(name="alex2", extra='sb'),
])
session.commit()

增

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

删

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()

改

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()ret = session.query(Users).filter(text("id<:value and name=:name")).params(value=224, name='fred').order_by(User.id).all()ret = session.query(Users).from_statement(text("SELECT * FROM users where name=:name")).params(name='ed').all()

查

#条件
ret = session.query(Users).filter_by(name='alex').all()
ret = session.query(Users).filter(Users.id > 1, Users.name == 'eric').all()
ret = session.query(Users).filter(Users.id.between(1, 3), Users.name == 'eric').all()
ret = session.query(Users).filter(Users.id.in_([1,3,4])).all()
ret = session.query(Users).filter(~Users.id.in_([1,3,4])).all()
ret = session.query(Users).filter(Users.id.in_(session.query(Users.id).filter_by(name='eric'))).all()
from sqlalchemy import and_, or_
ret = session.query(Users).filter(and_(Users.id > 3, Users.name == 'eric')).all()
ret = session.query(Users).filter(or_(Users.id < 2, Users.name == 'eric')).all()
ret = session.query(Users).filter(
or_(
Users.id < 2,
and_(Users.name == 'eric', Users.id > 3),
Users.extra != ""
)).all()# 通配符
ret = session.query(Users).filter(Users.name.like('e%')).all()
ret = session.query(Users).filter(~Users.name.like('e%')).all()# 限制
ret = session.query(Users)[1:2]# 排序
ret = session.query(Users).order_by(Users.name.desc()).all()
ret = session.query(Users).order_by(Users.name.desc(), Users.id.asc()).all()# 分组
from sqlalchemy.sql import funcret = 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()# 连表ret = session.query(Users, Favor).filter(Users.id == Favor.nid).all()ret = session.query(Person).join(Favor).all()ret = session.query(Person).join(Favor, isouter=True).all()# 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()