Python—sqlalchemy

时间：2021-12-05 09:59:28

SQLAlchemy

　　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。

#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:

'''

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...]

'''

1、使用 Schema Type/SQL Expression Language/Engine/ConnectionPooling/Dialect 进行数据库操作。

#!/usr/bin/env python

# -*- coding:utf-8 -*-

from sqlalchemy import create_engine, Table, Column, Integer, String, MetaData, ForeignKey,select

metadata = MetaData()

user = Table('pepole', metadata,

    Column('id', Integer, primary_key=True),

    Column('name', String(20)),

)

color = Table('color', metadata,

    Column('id', Integer, primary_key=True),

    Column('name', String(20)),

)

engine = create_engine("mysql+mysqldb://root:123456@172.16.8.47:3306/test" ,max_overflow=5)

#metadata.create_all(engine)创建表

conn = engine.connect()

#--增

#sql = user.insert().values(id=3, name='lisi')

#conn.execute(sql)

#conn.close()

#--删

#sql = user.delete().where(user.c.id == 1)

#conn.execute(sql)

#conn.close()

#--改

#sql = user.update().where(user.c.name == 'zhangsan').values(name='lisi')

#conn.execute(sql)

#conn.close()

#--查

#sql = select([user, ])

#sql = select([user.c.id, ])

#sql = select([user.c.name, color.c.name]).where(user.c.id==color.c.id)#查找user和color表中id相等的name

#sql = select([user.c.name]).order_by(user.c.name)

#result = conn.execute(sql)

#print result.fetchall()

2、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。

#!/usr/bin/env python

# -*- coding:utf-8 -*-

from sqlalchemy.ext.declarative import declarative_base

from sqlalchemy import Column, Integer, String

from sqlalchemy.orm import sessionmaker

from sqlalchemy import create_engine

engine = create_engine("mysql+mysqldb://root:123456@192.168.0.110:3306/test" ,max_overflow=5)#echo=True显示过程

Base = declarative_base()

class Host(Base):

    __tablename__ = 'hosts'

    id = Column(Integer, primary_key=True)

    name = Column(String(50))

# 寻找Base的所有子类，按照子类的结构在数据库中生成对应的数据表信息

Base.metadata.create_all(engine)

增、删、改、查

Session = sessionmaker(bind=engine)

session = Session()

#--------增

u = Host(id=2, name='zhansgan')

session.add(u)

session.add_all([

                 Host(id=3, name='lisi'),

                 Host(id=4, name='wangwu')

     ])

session.commit()
#--------删

session.query(Host).filter(Host.id > 2).delete()

session.commit()
#--------改

session.query(Host).filter(Host.id == 2).update({'name' : "wangwu"})

session.commit()
#--------查

result=session.query(Host).filter_by(id=2).first()#first()第一个 all()全部

print result

offs=session.query(Host).offset(1).all()#从第4条数据开始

print(offs)

ret = session.query(Host).order_by(Host.id).all()#排序

ret = session.query(Host).order_by(Host.id)[0:3]#找出前3条记录

print(ret)

session.commit()
query = session.query(Host.name)

print query.all()

print query.limit(1).all() # 最多返回 1 条记录

print query.offset(1).all() # 从第 2 条记录开始返回

print query.order_by(Host.name).all() # 排序

print query.order_by(Host.name.desc()).all()

filter其他常用功能：

equals

query.filter(User.name == 'ed')

not equals

query.filter(User.name != 'ed')

LIKE:

query.filter(User.name.like('%ed%'))

IN:

query.filter(User.name.in_(['ed', 'wendy', 'jack']))#在列表内存在就找出

# works with query objects too:

query.filter(User.name.in_(

　　　　　　session.query(User.name).filter(User.name.like('%ed%'))

))#先找出符合%ed%的列表在判断是否在该列表内

NOT IN:

query.filter(~User.name.in_(['ed', 'wendy', 'jack']))

IS NULL:

query.filter(User.name == None)

# alternatively, if pep8/linters are a concern

query.filter(User.name.is_(None))

IS NOT NULL:

query.filter(User.name != None)

# alternatively, if pep8/linters are a concern

query.filter(User.name.isnot(None))

AND:

from sqlalchemy import and_

query.filter(and_(User.name == 'ed', User.fullname == 'Ed Jones'))

OR:

from sqlalchemy import or_

query.filter(or_(User.name == 'ed', User.name == 'wendy'))

外键关联

一对多的关联引用parent.relationship()

class User(Base):

    __tablename__ = 'user'

    id = Column(Integer, primary_key=True)

    name = Column(String(50))

    group_id=Column(Integer,ForeignKey("group.id"))#关联

    group=relationship("Group",backref="group_list")#可以通过group获取Group表里的数据，backref:反向关联

class Group(Base):

    __tablename__ = 'group'

    id = Column(Integer, primary_key=True)

    name = Column(String(50))
#在表Group插入两个组

g1=Group(name="g1")

g2=Group(name="g2")

session.add_all([g1,g2])

session.commit()
#插入一个用户

g1=session.query(Group).filter(Group.name=="g1").first()

u = User(id=1, name='zhangsan',group_id=g1.id)

session.add(u)

#可以通过User表查看zhangsan在Group表里对应的组

h=session.query(User).filter(User.name=="zhangsan").first()

print(h.group.name)

relationship()中的backref（反向关联）

#查看g1组下有几个用户关联

gg=session.query(Group).filter(Group.name=="g1").first()

print(gg.group_list)

join查询

INNER JOIN:

aa=session.query(User).join(User.group).all()

print(aa)

aa=session.query(User).join(User.group).filter(Group.name=="g1").all()#加条件

print(aa)

多对多关联查询（需创建一个中间表）

#!/usr/bin/env python

# -*- coding:utf-8 -*-

from sqlalchemy.ext.declarative import declarative_base

from sqlalchemy import Column, Integer, String,ForeignKey,Table

from sqlalchemy.orm import sessionmaker,relationship

from sqlalchemy import create_engine

engine = create_engine("mysql+mysqldb://root:123456@172.16.8.47:3306/test" ,max_overflow=5)#echo=True显示过程

Base = declarative_base()

#创建中间表，关联另外两个表

HostGroup = Table("Host_Group",Base.metadata,

                  Column("host_id",ForeignKey("host.id"),primary_key=True),

                  Column("group_id",ForeignKey("group.id"),primary_key=True),

                  )

class Host(Base):

    __tablename__ = 'host'

    id = Column(Integer, primary_key=True)

    name = Column(String(50))

    #group_id=Column(Integer,ForeignKey("group.id"))

    group=relationship("Group",

                       secondary=HostGroup,#指定中间表的实例

                       backref="group_list")

    def __repr__(self):

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

class Group(Base):

    __tablename__ = 'group'

    id = Column(Integer, primary_key=True)

    name = Column(String(50),unique=True,nullable=False)

    def __repr__(self):

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

# 寻找Base的所有子类，按照子类的结构在数据库中生成对应的数据表信息

Base.metadata.create_all(engine)

创建组和主机

Session = sessionmaker(bind=engine)

session = Session()

#创建组

g1 = Group(name="g1")

g2 = Group(name="g2")

g3 = Group(name="g3")

session.add_all([g1,g2,g3])

#创建主机

h1 = Host(name="172.0.0.1")

h2 = Host(name="172.0.0.2")

h3 = Host(name="172.0.0.3")

session.add_all([h1,h2,h3])

进行关联

groups = session.query(Group).all()#找出所有组

h1=session.query(Host).filter(Host.name=="172.0.0.1").first()#找出h1

h2=session.query(Host).filter(Host.name=="172.0.0.2").first()#找出h2

h1.group=groups#h1关联3个组

h2.group=groups[1:-1]#h2关联两个组

查询

g1=session.query(Group).filter(Group.name=="g1").first()

h2=session.query(Host).filter(Host.name=="172.0.0.1").first()

print(g1.group_list)#查看g1组下有哪些主机

print(h2.group)#查看172.0.0.1属于哪些组

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