4.SQLAlchemy的使用

• 安装
  pip install SQLAlchemy
• 创建数据库

  create database test default charset utf8;
  

  • 此库的表参考3.pymysql的使用
• 使用SQLAlchemy的步骤
  1.创建到数据库的引擎
  2.生成实体类的基类
  3.创建实体类
  4.执行创建操作
  5.为了执行CRUD操作,需要创建到达数据库的会话类

  from sqlalchemy import create_engine, Column, Integer, String, Date, ForeignKey
  from sqlalchemy.ext.declarative import declarative_base
  from sqlalchemy.orm import sessionmaker
  # 创建到数据库的引擎
  engine = create_engine(
    # mysql+pymysql://用户名:密码@服务器/数据库?字符集参数
     'mysql+pymysql://root:[email protected]/test?charset=utf8',
    # 编码方案
    encoding='utf8',
    # echo=True   # 打开调试模式，生产环境不要设置
  )
  
  # 创建一个会话类，只有在CRUD，即增删改查时需要，本模  块文件实际上用不到
  # 为了在其他模块文件中可以直接调用，在本模块中创建
  Session = sessionmaker(bind=engine)
  
  # 生成实体类的基类
  Base = declarative_base()
  
  # 创建部门表的实体类，类名自定义，必须继承自Base
  class Departments(Base):
      __tablename__ = 'departments'  # 此类关联departments表
      dep_id = Column(Integer, primary_key=True)
      dep_name = Column(String(20), unique=True)
  
  # 创建员工表的实体类
  class Employees(Base):
      __tablename__ = 'employees'
      emp_id = Column(Integer, primary_key=True)
      emp_name = Column(String(20))
      birth_date = Column(Date)
      email = Column(String(50))
      # dep_id与departments的dep_id构成外键约束关系
      dep_id = Column(Integer, ForeignKey('departments.dep_id'))
  
  # 创建工资表的实体类
  class Salary(Base):
      __tablename__ = 'salary'
      id = Column(Integer, primary_key=True)
      date = Column(Date)
      emp_id = Column(Integer,ForeignKey('employees.emp_id'))
      basic = Column(Integer)
      awards = Column(Integer)
  
  if __name__ == '__main__':
      # 库中无表则创建，有表只是关联，不会再覆盖
      Base.metadata.create_all(engine)
    )
  

• 创建部门表的会话实例

  from dbconn import Departments, Employees, Salary, Session
  # 创建会话实例，用于连接数据库
  session = Session()
  # 创建部门实例
  hr = Departments(dep_id=1, dep_name='人事部')
  ops = Departments(dep_id=2, dep_name='运维部')
  dev = Departments(dep_id=3, dep_name='开发部')
  qa = Departments(dep_id=4, dep_name='测试部')
  finance = Departments(dep_id=5, dep_name='财务部')
  market = Departments(dep_id=6, dep_name='市场部')
  sales = Departments(dep_id=7, dep_name='销售部')
  # 在数据库中创建记录
  deps = [hr, ops, dev, qa, finance, market, sales]
  session.add_all(deps)
  session.commit()   # 确认至数据库
  
  # 关闭会话
  session.close()
  

• 创建员工信息表的会话实例

  from dbconn import Departments, Employees, Salay, Session
  
  #  创建会话实例，用于连接数据库
  session = Session()
  # 创建员工实例
  z1 = Employees(
     emp_id = 1,
     emp_name = '张一',
     birth_date = '1999-12-12',
     email = '[email protected]',
     dep_id = 1
  )
  
  z2 = Employees(
     emp_id = 2,
     emp_name = '张二',
     birth_date = '2000-12-12',
     email = '[email protected]',
     dep_id = 2
  )
  
  z3 = Employees(
     emp_id = 3,
     emp_name = '张三',
     birth_date = '2001-12-12',
     email = '[email protected]',
     dep_id = 3
  )
  
  z4 = Employees(
     emp_id = 4,
     emp_name = '张四',
     birth_date = '1994-12-12',
     email = '[email protected]',
     dep_id = 4
  )
  
  z5 = Employees(
     emp_id = 5,
     emp_name = '张五',
     birth_date = '1995-12-12',
     email = '[email protected]',
     dep_id = 3
  )    
  
  z6 = Employees(
     emp_id = 6,
     emp_name = '张六',
     birth_date = '1996-12-12',
     email = '[email protected]',
     dep_id = 5
  )
  
  z7 = Employees(
     emp_id = 7,
     emp_name = '张七',
     birth_date = '1997-12-12',
     email = '[email protected]',
     dep_id = 3
  )
  
  z8 = Employees(
     emp_id = 8,
     emp_name = '张八',
     birth_date = '1998-12-12',
     email = '[email protected]',
     dep_id = 2
  )
  
  # 在数据库中创建记录
  emps = [z1, z2, z3, z4, z5, z6, z7, z8]
  session.add_all(emps)
  session.commit()   # 确认至数据库
  
  # 关闭会话
  session.close()
  

• 对数据进行CRUD操作

  from dbconn import Session, Departments, Employees
  # 1. 创建一个会话实例
  session = Session()
  
  #################################
  # 查询数据库，返回实体类的实例
  # qset1 = session.query(Departments)
  # print(qset1)  # 此时只是一条SQL语句，不真正连接数据库
  # print(list(qset1))  # 取值的时候，才会连接数据库
  # for dep in qset1:
  #     print('部门ID: %s, 部门名称: %s' % (dep.dep_id,   dep.dep_name))  
  #################################
  # 如果查询某些字段，返回的是元组
  # qset2 = session.query(Employees.emp_name,   Employees.email)
  # print(qset2)   # qset2是SQL语句
  # print(list(qset2))   # 取值是元组
  #################################
  # 排序，可以对执行结果进一步操作
  # qset3 =     session.query(Departments).order_by(Departments.dep_id)  
  # for dep in qset3:
  #     print(dep.dep_id, dep.dep_name)
  #################################
  # 排序，取切片
  # qset4 = session.query(Departments).order_by(Departments.dep_id)[2:4]
  # print(qset4)  # 因为qset4执行了切片取值，所以它不是sql语句了
  # for dep in qset4:
  #     print(dep.dep_id, dep.dep_name)
  #################################
  # 过滤，查找2号部门的员工
  # qset5 =   session.query(Employees).filter(Employees.dep_id==2)
  # for emp in qset5:
  #     print(emp.emp_name, emp.email)
  #################################
  # 过滤，查找2号部门使用163邮箱的员工
  # qset6 = session.query(Employees).filter(Employees.dep_id==2)\
  #     .filter(Employees.email.like('%163.com'))
  # for emp in qset6:
  #     print(emp.emp_name, emp.email)
  #################################
  # all方法返回列表, first方法返回结果的第一项
  # qset7 =   session.query(Departments).order_by(Departments.dep_id)
  # print(qset7.all())
  # print(qset7.first())
  # dep = qset7.first()
  # print(dep.dep_id, dep.dep_name)
  #################################
  # 多表查询，查询员工所在部门
  # qset8 = session.query(Employees.emp_name,   Departments.dep_name)\
  #     .join(Departments)
  # for item in qset8:
  #     print(item)
  # 多表查询时，query的第一个参数是  Employees.emp_name，join时要写Departments  
  # 如果query的第一个参数是Departments.dep_name, join时要写Employees
  # qset9 = session.query(Departments.dep_name,     Employees.emp_name)\  
  #     .join(Employees)  
  # for item in qset9:
  #     print(item)
  #################################
  # 更新，首先找到记录对应的实例，然后对实例重新赋值即  可
    # 注意，filter的结果是列表的形式
    # qset10 = session.query(Departments).filter(Departments.dep_name=='  人事部')
  # hr = qset10[0]  # 从列表中取出第一个元素
  # hr.dep_name = '人力资源部'
  # session.commit()  # 增删改都要commit
  #################################
  # 删除，将7号部门删除
  qset11 = session.query(Departments).filter(Departments.dep_id==7)
  sales = qset11[0]
  session.delete(sales)
  session.commit()
  
  

以上代码,经过测试,可以正常运行,如有错误,请批评指正,不用客气.