【转】MySQL— pymysql and SQLAlchemy

#!/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='', db='t1')

# 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'")

  

# 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()

b. 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='', 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()

# 获取最新自增ID

new_id = cursor.lastrowid

cursor.close()

conn.close()

c. 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='', 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

d. fetch数据类型

关于默认获取的数据是元组类型，如果想要获得字典类型的数据，即：

#!/usr/bin/env python

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

import pymysql

  

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

二、SQLAlchemy

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。

1. 下载安装

#在终端直接运行

pip3 install SQLAlchemy

2. SQLAlchemy依赖关系

SQLAlchemy本身无法操作数据库，其必须依赖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。

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

3. 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。

a. 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

#表明依赖关系并创建连接，最大连接数为5 

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'    # 表名

    id = Column(Integer, primary_key=True,autoincrement=True)    # id列，主键自增

    name = Column(String(32))    # name列

    extra = Column(String(16))    # extra列

 

    __table_args__ = (

    UniqueConstraint('id', 'name', name='uix_id_name'),    # 创建联合唯一索引

        Index('ix_id_name', 'name', 'extra'),    # 创建普通索引

    )

 

 

# 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"))    # 创建外键

 

 

# 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'))    # 创建外键

    group_id = Column(Integer, ForeignKey('group.id'))    # 创建外键

 

 

def init_db():

    Base.metadata.create_all(engine)

 

 

def drop_db():

    Base.metadata.drop_all(engine)

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

b. 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)

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

b.1 增

#单条增加

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

session.add(obj)

#多条增加

session.add_all([

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

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

])

#提交

session.commit()

b.2 删

#先查询到要删除的记录，再delete

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

session.commit()

b.3 改

#先查询，再更新

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

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

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

session.commit()

b.4 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()

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()

b.5 其它

#　条件

ret = session.query(Users).filter_by(name='alex').all()    # 条件内为关键字表达式

ret = session.query(Users).filter(Users.id > 1, Users.name == 'eric').all()    # 条件内为SQL表达式

ret = session.query(Users).filter(Users.id.between(1, 3), Users.name == 'eric').all()    # between

ret = session.query(Users).filter(Users.id.in_([1,3,4])).all()    # in

ret = session.query(Users).filter(~Users.id.in_([1,3,4])).all()    # not in

ret = session.query(Users).filter(Users.id.in_(session.query(Users.id).filter_by(name='eric'))).all()    # 子查询条件

from sqlalchemy import and_, or_

ret = session.query(Users).filter(and_(Users.id > 3, Users.name == 'eric')).all()    # and

ret = session.query(Users).filter(or_(Users.id < 2, Users.name == 'eric')).all()    # or

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()    # e开头

ret = session.query(Users).filter(~Users.name.like('e%')).all()    # 非e开头

# 限制

ret = session.query(Users)[1:2]    # 相当于limit

# 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 func

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()

# 连表

ret = session.query(Users, Favor).filter(Users.id == Favor.nid).all()    # 笛卡儿积连表

ret = session.query(Person).join(Favor).all()    # 默认内连 inner join

ret = session.query(Person).join(Favor, isouter=True).all()    # 左连

# 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()

参考资料：

1. Python开发【第十九篇】：Python操作MySQL