python之sqlalchemy

                                                     

ORM:

ORM框架的作用就是把数据库表的一行记录与一个对象互相做自动转换。 正确使用ORM的前提是了解关系数据库的原理。 ORM就是把数据库表的行与相应的对象建立关联，互相转换。 由于关系数据库的多个表还可以用外键实现一对多、多对多等关联，相应地， ORM框架也可以提供两个对象之间的一对多、多对多等功能。

一 单表操作（不涉及一对多，多对多）

#coding:utf8
import sqlalchemy
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String
from sqlalchemy.orm import sessionmaker
print(sqlalchemy.__version__)


engine = create_engine('sqlite:///dbyuan1.db', echo=True)

Base = declarative_base()#生成一个SQLORM基类

class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    name = Column(String)
    fullname = Column(String)
    password = Column(String)

    def __repr__(self):
       return "<User(name='%s', fullname='%s', password='%s')>" % (
                            self.name, self.fullname, self.password)

Base.metadata.create_all(engine)  #创建所有表结构

ed_user = User(name='xiaoyu', fullname='Xiaoyu Liu', password='123')
print(ed_user)
#这两行触发sessionmaker类下的__call__方法，return得到 Session实例，赋给变量session，所以session可以调用Session类下的add，add_all等方法
MySession = sessionmaker(bind=engine)
session = MySession()

session.add(ed_user)
# our_user = session.query(User).filter_by(name='ed').first()
# SELECT * FROM users WHERE name="ed" LIMIT 1;
# session.add_all([
#     User(name='alex', fullname='Alex Li', password='456'),
#     User(name='alex', fullname='Alex old', password='789'),
#     User(name='peiqi', fullname='Peiqi Wu', password='sxsxsx')])

session.commit()

#print(">>>",session.query(User).filter_by(name='ed').first())
#print(session.query(User).all())
# for row in session.query(User).order_by(User.id):
#      print(row)
# for row in session.query(User).filter(User.name.in_(['alex', 'wendy', 'jack'])):＃这里的名字是完全匹配
#     print(row)
# for row in session.query(User).filter(~User.name.in_(['ed', 'wendy', 'jack'])):
#     print(row)
#print(session.query(User).filter(User.name == 'ed').count())
#from sqlalchemy import and_, or_

# for row in session.query(User).filter(and_(User.name == 'ed', User.fullname == 'Ed Jones')):
#     print(row)
# for row in session.query(User).filter(or_(User.name == 'ed', User.name == 'wendy')):
#     print(row)

 

 二  一对多的关联表操作

实例1:

#coding:utf8

import sqlalchemy
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String,ForeignKey
from sqlalchemy.orm import sessionmaker,relationship


engine = create_engine('sqlite:///dbyuan2.db', echo=True)

Base = declarative_base()

class Father(Base):
    __tablename__ = 'father'
#id = Column(Integer, primary_key=True)里的数据类型一定写整型(Integer)
    id = Column(Integer, primary_key=True)
    name = Column(String(20))
    def __repr__(self):
         return "<Father(name='%s')>" % self.name


class Son(Base):
    __tablename__ = 'son'

    id = Column(Integer, primary_key=True)
    name = Column(String(20))
    #ForeignKey建在多的一方
    father_id = Column(String(20), ForeignKey('father.id'))
    father=relationship("Father",backref="son", order_by=id)
    def __repr__(self):
         return "<Son(name='%s')>" % self.name

Base.metadata.create_all(engine)

Session = sessionmaker(bind=engine)
session = Session()


f1= Father(name='zhangsan')
f2= Father(name='lisi')
f3= Father(name='wangwu')

f1.son = [Son(name='zhangdasan'),Son(name='zhangersan')]


session.add(f1)
session.commit()

for u, a in session.query(Father, Son).\
                    filter(Father.id==Son.id).\
                    all():
    print u, a   #<Father(name='zhangsan')> <Son(name='zhangdasan')>

   

   

实例2:

#__ *__ coding:utf8__*__

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String,and_,or_,ForeignKey
from  sqlalchemy.orm import sessionmaker,relationship

Base = declarative_base() #生成一个SqlORM 基类


engine = create_engine('sqlite:///dbyuan3.db', echo=True)


class Host(Base):
    __tablename__ ='host'
    id = Column(Integer,primary_key=True,autoincrement=True)
    hostname = Column(String(64),unique=True,nullable=False)
    ip_addr = Column(String(128),unique=True,nullable=False)
    port = Column(Integer,default=22)
    #前提 一个主机只能属于一个组
    group_id=Column(Integer,ForeignKey('group.id'))
    group=relationship('Group',backref='host')
    def __repr__(self):
        return "id:%s hostname:%s port:%s"%(self.id,self.hostname,self.port)


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

    def __repr__(self):
        return "id:%s hostname:%s"%(self.id,self.name)


Base.metadata.create_all(engine) #创建所有表结构

if __name__ == '__main__':
    SessionCls = sessionmaker(bind=engine,autoflush=False)
    session = SessionCls()

    g1=Group(name='g1')
    g2=Group(name='g2')
    g3=Group(name='g3')
    session.add_all([g1,g2,g3])
    session.commit()

    h1 = Host(hostname='localhost',ip_addr='127.0.0.1',group_id=g1.id)#g1如果在这之前没有提交，group_id拿到的永远是一个空值
    h2 = Host(hostname='ubuntu',ip_addr='192.168.2.243',port=20000)
    session.add_all([h1,h2])

    session.commit()

    g1=session.query(Group).filter(Group.name=='g1').first()
    h=session.query(Host).filter(Host.hostname=='localhost').first()#注意要加上first()，否则报错，注意与all()结果的不同

    print "<<<",g2
    print ">>>",h

    print(h.group.name)
    print g1.host
    print g1.host[0].hostname

    #g2.host什么结果？（未绑定，无结果）

   

   

三 多对多的关联表操作

#!/usr/bin/env python
# -*- coding:utf-8 -*-

from sqlalchemy import create_engine,and_,or_,func,Table
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String,ForeignKey
from  sqlalchemy.orm import sessionmaker,relationship

Base = declarative_base() #生成一个SqlORM 基类


Host2Group = Table('host_2_group',Base.metadata,
    Column('host_id',ForeignKey('host.id'),primary_key=True),
    Column('group_id',ForeignKey('group.id'),primary_key=True),)


engine = create_engine('sqlite:///dbyuan4.db', echo=True)

class Host(Base):
    __tablename__ = 'host'

    id = Column(Integer,primary_key=True,autoincrement=True)
    hostname = Column(String(64),unique=True,nullable=False)
    ip_addr = Column(String(128),unique=True,nullable=False)
    port = Column(Integer,default=22)
    group = relationship('Group',
                          secondary=Host2Group,
                          backref='host_list')

    #group =relationship("Group",back_populates='host_list')
    def __repr__(self):
        return  "<id=%s,hostname=%s, ip_addr=%s>" %(self.id,
                                                    self.hostname,
                                                    self.ip_addr)
class Group(Base):
    __tablename__ = 'group'
    id = Column(Integer,primary_key=True)
    name = Column(String(64),unique=True,nullable=False)

    def __repr__(self):
        return  "<id=%s,name=%s>" %(self.id,self.name)

Base.metadata.create_all(engine) #创建所有表结构

if __name__ == '__main__':
    SessionCls = sessionmaker(bind=engine,autoflush=False)
    session = SessionCls()


    g1 = Group(name='g1')
    g2 = Group(name='g2')
    g3 = Group(name='g3')
    g4 = Group(name='g4')
    session.add_all([g1,g2,g3,g4])
    session.commit()


    #g4 = session.query(Group).filter(Group.name=='g4').first()
    #h = session.query(Host).filter(Host.hostname=='localhost').update({'group_id':g4.id})
    #h = session.query(Host).filter(Host.hostname=='localhost').first()
    #print("h1:",h.group.name )
    #print("g:",g4.host_list )


    h1 = Host(hostname='h1',ip_addr='192.168.1.56')
    h2 = Host(hostname='h2',ip_addr='192.168.1.57',port=10000)
    h3 = Host(hostname='ubuntu',ip_addr='192.168.1.58',port=10000)
    session.add_all([h1,h2,h3])
    session.commit()

    groups = session.query(Group).all()
    g1 = session.query(Group).first()

    h2 = session.query(Host).filter(Host.hostname=='h2').first()
    h2.group = groups[1:-1]
    print("===========>",h2.group)

    #objs = #session.query(Host).join(Host.group).group_by(Group.name).all()
    #objs = session.query(Host,func.count(Group.name)).\
    #join(Host.group).group_by(Group.name).all()
    #print("-->objs:",objs)
    #print("++>",obj)
    #obj.hostname = "test server"
    #session.delete(obj)
    #objs = session.query(Host).filter(and_(Host.hostname.like("ub%"), Host.port > 20)).all()

    session.commit()

　   

      

      

 

注意：

      1   Session = sessionmaker(bind=engine,autoflush=False) 

      2   session.add添加数据到数据后，一定要session.commit()后才能增删改查，否则结果只能为none

      3   session.query(Group).filter(Group.name=='g1').first() 注意有无first()的区别

 

 

再注意：

       1   关于 session.add   session.query   session.commit的顺序问题？

就是说在同一个会话中， insert into table (xxxx)后，可以select * from xxx;可以查询到插入的数据，只是不能在其他会话，比如我另开一个客户端去连接数据库不能查询到刚刚插入的数据。

这个数据已经到数据库。值是数据库吧这个数据给锁了。只有插入数据的那个session可以查看到，其他的session不能查看到，可以理解提交并解锁吧。

      2  第三张表必须利用table创建吗？NO

      3   联合唯一

      4   一对多的第二个例子，如何理解去掉第一个commit后就报错的现象