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[Java教程]Python操作MySQL


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

#!/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IDnew_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:

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_basefrom sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Indexfrom sqlalchemy.orm import sessionmaker, relationshipfrom sqlalchemy import create_engineengine = 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-8 -*-from sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Indexfrom sqlalchemy.orm import sessionmaker, relationshipfrom sqlalchemy import create_engineengine = 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'),  )  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)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()

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

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  • session.query(Users).filter(Users.id > 2).update({"name" : "099"})session.query(Users).filter(Users.id > 2).update({Users.name: Users.name + "099"}, synchronize_session=False)session.query(Users).filter(Users.id > 2).update({"num": Users.num + 1}, synchronize_session="evaluate")session.commit()

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  • 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()

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  • 其他
    # 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()

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更多功能参见文档,猛击这里下载PDF