MySQL— pymysql and SQLAlchemy

Posted 2021-01-24 langqi250

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#!/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=\'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：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" : "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()    # 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()