搜索
您的当前位置：首页正文

MySQL—pymysqlandSQLAlchemy

2020-11-09 来源：二三四教育网

目录

一、pymysql

二、SQLAlchemy

一、pymysql

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

1. 下载安装

#在终端直接运行
pip3 install pymysql

2. 使用操作

a. 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='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()# 获取最新自增IDnew_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='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

    • 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='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()

    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：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_basefrom sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Indexfrom sqlalchemy.orm import sessionmaker, relationshipfrom 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_basefrom sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Indexfrom sqlalchemy.orm import sessionmaker, relationshipfrom 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deletesession.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" : "099"}) # 直接更改session.query(Users).filter(Users.id > 2).update({Users.name: Users.name + "099"}, 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() # betweenret = session.query(Users).filter(Users.id.in_([1,3,4])).all() # inret = session.query(Users).filter(~Users.id.in_([1,3,4])).all() # not inret = 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() # andret = session.query(Users).filter(or_(Users.id < 2, Users.name == 'eric')).all() # orret = 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 joinret = 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

    Copyright © 2019- how234.cn 版权所有
    赣ICP备2023008801号-2

    Top