python成长之路13

一：SqlAlchemy ORM　　

ORM：Object Relational Mapping 对象关系映射是一种程序技术，用于实现面向对象编程语言里不同类型系统的数据之间的转换

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：

建立在SQL AQI至上，不需要写原生SQL语句，是将对象封装并转成原生语句

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  #适用于python 2使用MySQL-python模块
    mysql+mysqldb://<user>:<password>@<host>[:<port>]/<dbname>

pymysql #适用于python 3，因为python 3里面的mysql模块变为pymysql
    mysql+pymysql://<username>:<password>@<host>/<dbname>[?<options>]

MySQL-Connector #使用mysql connector连接数据库
    mysql+mysqlconnector://<user>:<password>@<host>[:<port>]/<dbname>

cx_Oracle #连接到oracle数据库
    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

1、使用 sqlalchemy + pymysql创建表：

import pymysql
from sqlalchemy import create_engine, Table, Column, Integer, String, MetaData, ForeignKey
metadata = MetaData()
#创建user和color两个表，metadata封装语句
user = Table('user', 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+pymysql://root:zhang@123@localhost:3306/test", max_overflow=5) #连接到数据库，最大连接池5个
metadata.create_all(engine) #创建数据库

2、增加数据：

import pymysql
from sqlalchemy import create_engine, Table, Column, Integer, String, MetaData, ForeignKey
metadata = MetaData()
user = Table('user', 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+pymysql://root:zhang@123@localhost:3306/test", max_overflow=5)
conn = engine.connect()
sql = user.insert().values(id=1,name='wu') #id可以不写，会自增
conn.execute(sql)
conn.close()

数据库验证：

3、删除数据：

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

import pymysql
from sqlalchemy import create_engine, Table, Column, Integer, String, MetaData, ForeignKey
metadata = MetaData()
user = Table('user', 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+pymysql://root:zhang@123@localhost:3306/test", max_overflow=5)
conn = engine.connect()

sql1 = user.delete().where(user.c.id == 1) #匹配id为1
sql2 = user.delete().where(user.c.name == 'li') #匹配条件name为li
conn.execute(sql1) #执行语句
conn.execute(sql2)
conn.close()

4、改数据：

import pymysql
from sqlalchemy import create_engine, Table, Column, Integer, String, MetaData, ForeignKey
metadata = MetaData()
user = Table('user', 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+pymysql://root:zhang@123@localhost:3306/test", max_overflow=5)
conn = engine.connect()

#sql1 = user.insert().values(name="zhang") #添加数据
sql1 = user.update().where(user.c.name == 'zhang').values(name='jack') #匹配套件并改数据
conn.execute(sql1)
conn.close()

5、查数据：

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

import pymysql
from sqlalchemy import create_engine, select,Table, Column, Integer, String, MetaData, ForeignKey
metadata = MetaData()
user = Table('user', 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+pymysql://root:zhang@123@localhost:3306/test", max_overflow=5)
conn = engine.connect()
sql = select([user,])
res = conn.execute(sql)
print(res.fetchall())
conn.close()

实际使用方法介绍：

创建表并插入数据：

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

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

Base = declarative_base() #生成一个SqlORM 基类
engine = create_engine("mysql+pymysql://root:zhang@123@localhost:3306/test",echo=True)

class Host(Base):
    __tablename__ = 'hosts'
    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)

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

if __name__ == '__main__':
    SessionCls = sessionmaker(bind=engine) #创建与数据库的会话session class ,注意,这里返回给session的是个class,不是实例
    session = SessionCls()
    h1 = Host(hostname='localhost',ip_addr='127.0.0.1')
    h2 = Host(hostname='Centos',ip_addr='192.168.10.254',port=2021)
    session.add_all([h1,h2])
    session.commit() #提交

查询并更改数据：

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

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

Base = declarative_base() #生成一个SqlORM 基类
engine = create_engine("mysql+pymysql://root:zhang@123@localhost:3306/test",echo=True)

class Host(Base):
    __tablename__ = 'hosts'
    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)

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

if __name__ == '__main__':
    SessionCls = sessionmaker(bind=engine) #创建与数据库的会话session class ,注意,这里返回给session的是个class,不是实例
    session = SessionCls()
    h1 = Host(hostname='localhost',ip_addr='127.0.0.1')
    h2 = Host(hostname='Centos',ip_addr='192.168.10.254',port=2021)
    session.add_all([h1,h2])

    #session.rollback()
    #h3 = Host(hostname='ubuntu2',ip_addr='192.168.2.244',port=20000)
    #session.add(h3)
    #session.add_all( [h1,h2])
    #h2.hostname = 'ubuntu_test' #只要没提交,此时修改也没问题

    res = session.query(Host).filter(Host.hostname.in_(['ubuntu2','localhost'])).first() #all所有，first第一个，last最后一个

    #res.hostname = "test hostname" #将查到的数据改值
    session.delete(res) #删除查询到的数据
    session.commit() #提交

ORM 外键关联多对多: 一个组可以包含多个主机，一个主机也可以在多个组，即一个主机可以在多个组里面，如下：

class Parent(Base):  #父类
    __tablename__ = 'parent'
    id = Column(Integer, primary_key=True)
    children = relationship("Child")

class Child(Base):  #子类
    __tablename__ = 'child'  #定义表名称
    id = Column(Integer, primary_key=True)  #id的值类型
    parent_id = Column(Integer, ForeignKey('parent.id'))  #关联父类的'parent.id即可完成与父类的外键关联

测试；

sqlalchemy无法在已经存在的表里面增加新的字段，因此可以将表删除重新创建，或自己使用原生SQL语句创建，也可以使用sqlalchemy的三方工具，我们这里将以前的表删除再重建：

mysql> drop tables  hosts;
Query OK, 0 rows affected (0.22 sec)

Pyhton 代码：

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

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

Base = declarative_base() #生成一个SqlORM 基类
engine = create_engine("mysql+pymysql://root:zhang@123@localhost:3306/test",echo=True)

class Host(Base):
    __tablename__ = 'hosts'
    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_id = Column(Integer, ForeignKey('group.id'))

class Group(Base):
    __tablename__ = 'group'
    id = Column(Integer,primary_key=True)
    name = Column(String(64),unique=True,nullable=False)
    child_id = Column(Integer)
Base.metadata.create_all(engine) #创建所有表结构

if __name__ == '__main__':
    SessionCls = sessionmaker(bind=engine) #创建与数据库的会话session class ,注意,这里返回给session的是个class,不是实例
    session = SessionCls()
    session.commit() #提交

验证：

mysql> desc hosts;
+----------+--------------+------+-----+---------+----------------+
| Field    | Type         | Null | Key | Default | Extra          |
+----------+--------------+------+-----+---------+----------------+
| id       | int(11)      | NO   | PRI | NULL    | auto_increment |
| hostname | varchar(64)  | NO   | UNI | NULL    |                |
| ip_addr  | varchar(128) | NO   | UNI | NULL    |                |
| port     | int(11)      | YES  |     | NULL    |                |
| group_id | int(11)      | YES  | MUL | NULL    |                |
+----------+--------------+------+-----+---------+----------------+
5 rows in set (0.01 sec) 
#group_id 行的Key的值是Mul

查看group表：

mysql> desc test.group;
+----------+-------------+------+-----+---------+----------------+
| Field    | Type        | Null | Key | Default | Extra          |
+----------+-------------+------+-----+---------+----------------+
| id       | int(11)     | NO   | PRI | NULL    | auto_increment |
| name     | varchar(64) | NO   | UNI | NULL    |                |
| child_id | int(11)     | YES  |     | NULL    |                |
+----------+-------------+------+-----+---------+----------------+
3 rows in set (0.01 sec)

创建关联的数据：

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

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

Base = declarative_base() #生成一个SqlORM 基类
engine = create_engine("mysql+pymysql://root:zhang@123@localhost:3306/test",echo=True)

class Host(Base):
    __tablename__ = 'hosts'
    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_id = Column(Integer, ForeignKey('group.id'))

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

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

if __name__ == '__main__':
    SessionCls = sessionmaker(bind=engine) #创建与数据库的会话session class ,注意,这里返回给session的是个class,不是实例
    session = SessionCls()

    g3 = Group(name='g3')
    session.add_all([g3,])
    h1 = Host(hostname='localhost',ip_addr='1.1.1.1',group_id=g3.id) #由于数据库还没有g3的内容，所以这样关联不成功
    session.add_all([h1,])
    session.commit() #提交

更改关联数据：

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

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

Base = declarative_base() #生成一个SqlORM 基类
engine = create_engine("mysql+pymysql://root:zhang@123@localhost:3306/test",echo=True)

class Host(Base):
    __tablename__ = 'hosts'
    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_id = Column(Integer, ForeignKey('group.id'))

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

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

if __name__ == '__main__':
    SessionCls = sessionmaker(bind=engine) #创建与数据库的会话session class ,注意,这里返回给session的是个class,不是实例
    session = SessionCls()
    g3 = session.query(Group).filter(Group.name=='g3').first()  #查到一个已经存在的组
    h = session.query(Host).filter(Host.hostname=='localhost').update({'group_id': g3.id}) #查到一个主机的信息并更新其group_id为上一步查到的组的id，即完成了外键的管理
    session.commit() #提交