Python ORM框架之SQLALchemy

ORM框架本质: 让面向对象的类跟数据库中的表做个对应关系

ORM与原生SQL比较：

1. 原生SQL性能较好
2. 原生SQL的可维护性相对差一些
3. ORM操作、开发起来比较简单、快捷

Python ORM框架：SQLALchemy、Django、Storm、SQLObject

SQLALchemy与Django比较：

• Django操作起来更简单，双下划线跨表查询更方便
• Django支持自动生成第三张表
• SQLALchemy更接近原生SQL
• 两者都是通过DB API（pymysql 、mysqlDB）模块连接数据库
• 默认SQLALchemy不能修改表的字段，只能创建表、删除表

SQLALchemy框架：

•  Engine： 框架的引擎
• Connection Pooling ： 数据库连接池
• Dialect ： 选择连接数据库的DB API类型
• Schema / Type ： 架构和类型
• SQL Expression Language： SQL表达式语言

SQLALchemy本身无法操作数据库，需要依赖pymysql第三方模块，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

使用pymysql连接数据库格式：

    mysql+pymysql://<username>:<password>@<host>/<dbname>[?<options>]

 

import datetime
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, Text, ForeignKey, DateTime, UniqueConstraint, Index
from sqlalchemy.orm import relationship, sessionmaker
from sqlalchemy.sql import text

Base = declarative_base()


class Users(Base):
    """
    单表创建
    """
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String(32), index=True, nullable=False)
    email = Column(String(32), unique=True)
    ctime = Column(DateTime, default=datetime.datetime.now)
    extra = Column(Text, nullable=True)

    __table_args__ = (
        UniqueConstraint('id', 'name', name='uix_id_name'),
        Index('ix_id_name', 'name', 'email'),
    )


# 一对多示例
class Hobby(Base):
    __tablename__ = 'hobby'
    id = Column(Integer, primary_key=True)
    caption = Column(String(50), nullable=True)


class Person(Base):
    __tablename__ = 'person'
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String(32), nullable=False)
    hobby_id = Column(Integer, ForeignKey("hobby.id"))  # hobby.id 中的hobby指的是tablename

    # 与生成表结构无关， 仅用于查询方便
    hobby = relationship('Hobby', backref='pers')  # 此处Hobby指的是类名


# 多对多示例
class Server(Base):
    __tablename__ = 'server'
    id = Column(Integer, primary_key=True, autoincrement=True)
    hostname = Column(String(64), unique=True, nullable=False)


class Group(Base):
    __tablename__ = 'group'
    id = Column(Integer, primary_key=True)
    name = Column(String(64), unique=True, nullable=False)

    # 与生成表无关，仅用于查询方便
    servers = relationship('Server', secondary='server2group', backref='groups')


class Server2Grouop(Base):
    __tablename__ = 'server2group'
    id = Column(Integer, primary_key=True, autoincrement=True)
    server_id = Column(Integer, ForeignKey('server.id'))
    group_id = Column(Integer, ForeignKey('group.id'))


def init_db():
    """
    根据类创建数据库表
    :return:
    """
    engine = create_engine(
        'mysql+pymysql://root:mysql@127.0.0.1:3306/t1?charset=utf8',
        max_overflow=0,  # 超过连接池大小后 最多创建的连接
        pool_size=3,  # 连接池大小
        pool_timeout=10,  # 连接池中没有线程最多等待时间，否则报错
        pool_recycle=-1,  # 多久对线程池进行一次连接回收
    )
    Base.metadata.create_all(engine)


def drop_db():
    """
    根据类删除数据库表
    :return:
    """
    engine = create_engine(
        'mysql+pymysql://root:mysql@127.0.0.1:3306/t1?charset=utf-8',
        max_overflow=0,
        pool_size=3,
        pool_timeout=5,
        pool_recycle=-1,
    )
    Base.metadata.drop_all(engine)

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.sql import text

Base = declarative_base()

#  基本增删改查示例
def db_action():
    """
    基本数据库操作
    :return:
    """
    engine = create_engine(
        'mysql+pymysql://root:mysql@127.0.0.1:3306/t1?charset=utf8',
        max_overflow=0,
        pool_size=3,
        pool_timeout=5,
        pool_recycle=-1,
    )
    Session = sessionmaker(bind=engine)

    session = Session()

    # 添加操作
    obj1 = Users(name='AABB')
    session.add(obj1)

    session.add_all([
        Users(name='tom'),
        Users(name='lily'),
        Users(name='oobb'),
    ])
    session.commit()

    # 删除操作
    session.query(Users).filter(Users.id > 2).delete()
    session.commit()

    # 修改操作
    session.query(Users).filter(Users.id > 0).update({"name": "110"})
    session.query(Users).filter(Users.id > 0).update({Users.name: Users.name + "110"}, synchronize_session=False)
    session.query(Users).filter(Users.id > 0).update({"age": Users.age + 1}, synchronize_session="evaluate")
    session.commit()

    # 查询操作
    r1 = session.query(Users).all()
    r2 = session.query(Users.name.label('别名'), Users.email).all()
    r3 = session.query(Users).filter(Users.name == 'OOBB').all()
    r4 = session.query(Users).filter_by(name='oobb').all()
    r5 = session.query(Users).filter_by(name='oobb').first()
    r6 = session.query(Users).filter(text("id<:value and name=:name")).params(value=110, name='aa').order_by(
        Users.id).all()
    r7 = session.query(Users).from_statement(text("select * from users where name=:name")).params(name='oobb').all()

    # 常用操作
    # [条件查询]
    m1 = session.query(Users).filter_by(name='oouu').all()
    m2 = session.query(Users).filter(Users.id > 1, Users.name == 'yyuu').all()
    m3 = session.query(Users).filter(Users.id.between(1, 5, 2), Users.email == 'cc@qq.com').all()
    m4 = session.query(Users).filter(Users.id.in_([1, 2, 5])).all()
    m5 = session.query(Users).filter(~Users.id.in_([2, 3, 4])).all()  # not in
    m6 = session.query(Users).filter(Users.id.in_(session.query(Users.id).filter_by(name='aa'))).all()


    from sqlalchemy import and_, or_

    m7 = session.query(Users).filter(and_(Users.id > 10, Users.name == 'oo')).all()
    m8 = session.query(Users).filter(or_(Users.id < 2, Users.email=='cc@qq.com')).all()
    m9 = session.query(Users).filter(
        or_(
            Users.id < 3,
            and_(Users.email=='cc@qq.com', Users.name=='cc'),
            Users.extra !=''
        )
    )

    # 通配符
    n = session.query(Users).filter(Users.name.like('m%')).all()
    n1 = session.query(Users).filter(~Users.name.like('m%')).all()

    # 限制
    n2 = session.query(Users)[1:5]

    # 排序
    n3 = session.query(Users).order_by(Users.id.desc()).all()
    n4 = session.query(Users).order_by(Users.id.desc(), Users.name.asc()).all()

    # 跨表查询
    a = session.query(Hobby, Person).filter(Hobby.id == Person.hobby_id).all()
    a1 = session.query(Person).join(Hobby).all()
    a2 = session.query(Person).join(Hobby, isouter=True).all()

    # 组合查询
    b = session.query(Person.name).filter(Person.id>2)
    b1 = session.query(Hobby.caption).filter(Hobby.id<10)
    result = b.union(b1).all()
    result2 = b.union_all(b1).all()