• ORM框架SQLAchemy的使用


    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:

    1
    pip3 install SQLAlchemy

    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:

    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

    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()

    表结构 + 数据库连接


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

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

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

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

    • 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()

      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()

    • 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()


      复制代码
      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()
      复制代码
    • 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()

      复制代码
      # 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()
     
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  • 原文地址:https://www.cnblogs.com/mashuqi/p/16035359.html
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