Python开发【第十九篇】：Python操作MySQL

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：

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：

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。

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

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_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()

• 增
  

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

  View Code
• 删
  

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

  View Code
• 改
  

  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()

  View Code
• 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()

  View Code
• 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 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()
  
  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()

  View Code

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Python开发【第十九篇】：Python操作MySQL

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