Python-ORM-SQLALchemy

ORM（object relational mopper）:关系对象映射。
作用：将对象转换成SQL语句，然后使用数据API执行SQL并获取执行结果。

SQLALchemy：是python提供的一个ORM模块，用来将对象转化为sql语句来操作数据库，其处于DB-API之上；

下面对上图执行步骤进行层层模拟：

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

准备工作安装，
依然是使用pip安装
pip install SQLAlchemy

第一步：
Engine使用ConnectionPooling连接数据库，然后再通过Dialect执行SQL语句。

#!/usr/bin/env python# -- coding = 'utf-8' --# Author Allen Lee# Python Version 3.5.1# OS Windows 7from  sqlalchemy import create_engine#创建连接engine = create_engine('mysql+pymysql://root:123@127.0.0.1:3306/mytest',max_overflow=3)#插入单条数据engine_execute(    "insert into  my_test (host,name) values ('127.0.0.1','Meta')")#插入多条数据engine_execute(    "insert into my_test (host,name) values (%s,%s)",(('192.168.132.127','Allen'),('10.0.0.32','Natasha'),))engine_execute(    "insert into my_test (host,name) VALUES (%(ip)s,%(username)s)",ip="10.127.2.66," , username='tl_ccs')#将执行结果返回给一个对象，然后在通过它的fetchall方法获取结果result = engine.execute("select * from my_test")result.fetchall()#查看数据库连接ret = engine_execute("show status like 'Threads% '")#事务操作with engine.begin() as conn:    conn.execute("insert into table (a,b,c) values (123,321,312)")    conn.execute("my_first_procedure(3)")conn = engine.connect()with conn.begin():    conn.execute("some statsment",{'a':2,'b':321})

第二步：
ngine使用Schema Type创建一个特定的结构对象，之后通过SQL Expression Language将该对象转换成SQL语句，然后通过 ConnectionPooling 连接数据库，再然后通过 Dialect 执行SQL，并获取结果。

# #!/usr/bin/env python# # -- coding = 'utf-8' --# # Author Allen Lee# # Python Version 3.5.1# # OS Windows 7#!/usr/bin/env python# -*- coding:utf-8 -*-from sqlalchemy import create_engine, Table, Column, Integer, String, MetaData, ForeignKeymetadata = 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:123@127.0.0.1:3306/mytest", max_overflow=5)conn = engine.connect()# 创建SQL语句，INSERT INTO "user" (id, name) VALUES (:id, :name)conn.execute(user.insert(),{'id':7,'name':'seven'})#增# sql = user.insert().values(id=123, name='wu')#删# sql = user.delete().where(user.c.id > 1)#改# sql = user.update().values(fullname=user.c.name)# sql = user.update().where(user.c.name == 'jack').values(name='ed')#查sql = select([user.c.name, color.c.name]).where(user.c.id==color.c.id)# sql = select([user.c.name]).order_by(user.c.name)# sql = select([user]).group_by(user.c.name)#获取查询结果result = conn.execute(sql)print(result.fetchall())#关闭连接conn.close()

第三步：
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' --# # Author Allen Lee# # Python Version 3.5.1# # OS Windows 7#!/usr/bin/env python# -*- coding:utf-8 -*-from sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy import Column, Integer, Stringfrom sqlalchemy.orm import sessionmakerfrom sqlalchemy import create_engineengine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/my_test", max_overflow=5)Base = declarative_base()class User(Base):    __tablename__ = 'users'    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)Session = sessionmaker(bind=engine)session = Session()########## 增 ##########u = User(id=2, name='allen')session.add(u)session.add_all([    User(id=3, name='natasha'),    User(id=4, name='meta')])session.commit()########## 删除 ##########session.query(User).filter(User.id > 2).delete()session.commit()########## 修改 ##########session.query(User).filter(User.id > 2).update({'cluster_id' : 0})session.commit()########## 查 ##########ret = session.query(User).filter_by(name='allen').first()ret = session.query(User).filter_by(name='meta').all()print(ret)ret = session.query(User).filter(User.name.in_(['natasha','allen'])).all()print(ret)ret = session.query(User.name.label('name_label')).all()print(ret,type(ret))ret = session.query(User).order_by(User.id).all()print(ret)ret = session.query(User).order_by(User.id)[1:3]print(ret)session.commit()