python 学习笔记十一 SQLALchemy ORM(进阶篇)

SqlAlchemy ORM　　

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.

Python MySQL API (DBAPI)

通过 pymysql 连接管理mysql

create table students
    (
        id int  not null auto_increment primary key,
        name char(8) not null,
        sex char(4) not null,
        age tinyint unsigned not null,
        tel char(13) null default "-"
    );

创建表

1.插入数据

import pymysql

conn  = pymysql.connect("127.0.0.1",user='root',db='test')

cur = conn.cursor()

recount = cur.execute("insert into students(name,sex,age,tel) values('koka','man',18,'10000')")
recount2 = cur.execute("insert into students(name,sex,age,tel) values('akok','man',20,'10010')")

li = [    ("hehe","man",11,"110"), ("xixi","falme",12,"112")]
recount3 = cur.executemany("insert into students(name,sex,age,tel) values(%s,%s,%s,%s)",li)

conn.commit()
cur.close()
conn.close()

print(recount, recount2, recount3)

2.删除数据

import pymysql 

conn = pymysql.connect("127.0.0.1",user='root',db='test') 
cur = conn.cursor()

recount = cur.execute("delete from students where name='akok';")

conn.commit()
cur.close()
conn.close()

3.修改数据

import pymysql 

conn = pymysql.connect("127.0.0.1",user='root',db='test') 
cur = conn.cursor()

recount = cur.execute("update students set age=24 where name='alex';")

conn.commit()
cur.close()
conn.close()

4.查数据

import pymysql 

conn = pymysql.connect("127.0.0.1",user='root',db='test') 
cur = conn.cursor()

recount = cur.execute("update students set age=24 where name='alex';")
recount = cur.execute("select * from students;")
print(cur.fetchone()) #匹配一条
print(cur.fetchone())
#cur.scroll(-1,mode="relative") #回退一条
print(cur.fetchone())
print(cur.fetchone())
cur.scroll(0,mode='absolute')#重置
print(cur.fetchone())
print(cur.fetchone())

conn.commit()
cur.close()
conn.close()

############################## fetchall  ##############################
import pymysql 

conn = pymysql.connect("127.0.0.1",user='root',db='test') 
cur = conn.cursor()
recount = cur.execute("select * from user;")
nret = cur.fetchall() #所有查询到的数据以元组返回
conn.commit()
cur.close()
conn.close()
print(nret)
for i in nret:
    print(i[0],i[1])

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

步骤一：

使用 Engine/ConnectionPooling/Dialect 进行数据库操作，Engine使用ConnectionPooling连接数据库，然后再通过Dialect执行SQL语句。

from sqlalchemy import create_engine
import pymysql

engine = create_engine("mysql+pymysql://root@127.0.0.1:3306/test",max_overflow=5)

engine.execute(
        "INSERT INTO hosts (hostname,ip_addr,port,group_id) VALUES ('web4','4.4.4.4',22,3)"
)

result = engine.execute("select * from hosts")

result.fetchall()

步骤二：

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

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

#生成metadata类
metadata = MetaData()

#创建user表，继承metadata类
#Engine使用Schama Type创建一个特定的结构对象
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)))

#通过ConnectionPooling 连接数据库
engine = create_engine("mysql+pymysql://root@127.0.0.1:3306/test", max_overflow=5,echo=True)
#通过Dialect执行SQL
#metadata.create_all(engine) #创建表结构

增删改查操作

""""增删改查"""""
conn = engine.connect()

#conn.execute(user.insert(),{'id':2,"name":"koka"})
#conn.close()

#sql = user.insert().values(id=2, name='akok')
#conn.execute(sql)
#conn.close()

#sql = user.delete().where(user.c.id >1)
#conn.execute(sql)
#conn.close()

#sql = user.update().values(fullname=user.c.name)
#sql = user.update().where(user.c.name == "koka").values(name="okak")
#conn.execute(sql)
#conn.close()

#sql = select([user, ]) => selct * from user

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

#sql = select([user.c.name,color.c.name]).where(user.c.id==color.c.id) =>
#SELECT user.name, color.name FROM user, color WHERE user.id = color.id

#sql = select([user.c.name]).order_by(user.c.name) =>
#SELECT user.name FROM user ORDER BY user.name

#sql = select([user, ]).group_by(user.c.name) =>
#SELECT user.id, user.name FROM user GROUP BY user.name

#conn.execute(sql)
#conn.close()

实例：

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

Base = declarative_base() #生成一个SQLORM基类

engine = create_engine("mysql+pymysql://root@127.0.0.1:3306/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)

    def __repr__(self):
        return "<Host(hostname='%s',ip_addr='%s')>" % (self.hostname,self.ip_addr)

"""
# 无法删除之前创建的hosts表，
# 这可能是MySQL在InnoDB中设置了foreign key关联，造成无法更新或删除数据。
# 可以通过设置FOREIGN_KEY_CHECKS变量来避免这种情况。
# SET FOREIGN_KEY_CHECKS = 0;

CREATE TABLE hosts (
    id INTEGER NOT NULL AUTO_INCREMENT,
    hostname VARCHAR(64) NOT NULL,
    ip_addr VARCHAR(128) NOT NULL,
    port INTEGER,
    PRIMARY KEY (id),
    UNIQUE (hostname),
    UNIQUE (ip_addr)
)
"""

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

if __name__ == "__main__":
    SessionCls = sessionmaker(bind=engine) 
    session = SessionCls()
    #h1 = Host(hostname="localhost", ip_addr="127.0.0.1")
    #h2 = Host(hostname="mysql", ip_addr="1.1.1.1", port=3306)
    #h3 = Host(hostname="web", ip_addr="10.0.0.10", port=8080)
    #session.add(h1)
    #h2.hostname = "mysqldb" #只要没提交,此时修改也没问题
    #session.add_all([h1, h2, h3])
    #session.rollback()
    #session.commit()

    res = session.query(Host).filter(Host.hostname.in_(["localhost", "mysqldb"])).all()
    print(res)
    """
    [<Host(hostname='localhost',ip_addr='127.0.0.1')>, <Host(hostname='mysqldb',ip_addr='1.1.1.1')>]
    """

更多内容详见：

http://www.jianshu.com/p/e6bba189fcbd

http://docs.sqlalchemy.org/en/latest/core/expression_api.html

注：SQLAlchemy无法修改表结构，如果需要可以使用SQLAlchemy开发者开源的另外一个软件Alembic来完成.

步骤三：

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。

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

engine = create_engine("mysql+pymysql://root@127.0.0.1:3306/test", max_overflow=5, echo=True) #echo显示sql语句创建过程

Base = declarative_base() #生成一个SQLORM基类

#创建表
class User(Base):
    __tablename__ = "users"
    id = Column(Integer, primary_key=True)
    name = Column(String(50))
    def __repr__(self):
        return "<User(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)

if __name__ == "__main__":
    Session = sessionmaker(bind=engine)
    session = Session()
    #增
    #sql1 = User(id=1,name="haha")
    #sql2 = User(id=2,name="hehe")
    #session.add(sql1)
    #session.add_all([sql1, sql2])
    #session.commit()

    #改
    #session.query(User).filter(User.id >1).update({"name":"xixi"})
    #session.commit()

    #删
    #session.query(User).filter(User.id == 1).delete()
    #session.commit()

    #查
    r1 = session.query(User).filter_by(name="xixi").first()

    r2 = session.query(User).filter_by(name="xixi").all()

    r3 = session.query(User).filter(User.name.in_(["haha", "hehe", "xixi"])).all()

    r4 = session.query(User.name.label("name_label")).all()
    #SELECT users.name AS name_label FROM users


    r5 = session.query(User).order_by(User.id).all()
    #SELECT users.id AS users_id, users.name AS users_name FROM users ORDER BY users.id

    r6 = session.query(User).order_by(User.id)[1:2]
    #SELECT users.id AS users_id, users.name AS users_name FROM users ORDER BY users.id LIMIT 1,2


    print(r1, r2, r3, r4, r5, r6)
    session.commit()

外键关联

FOREIGN KEY 约束是大多数(但不是所有)的关系型数据库中可以链接到主键列，或者拥有UNIQUE约束的列。
FOREIGN KEY 能够引用多重列主键，并且其自身拥有多重列，被称为“复合外键”(composite foreign key)。其也能够引用这些列的子集(subset)。
FOREIGN KEY 列作为对于其引用的列或者行的变化的响应能够自动更新其自。
FOREIGN KEY 能够引用其自身的表，这个就涉及到“自引用”(self-referential)的外键了。

一多对关系表，一个主机属于一个组，一个组可以拥有多个主机

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

engine = create_engine("mysql+pymysql://root@127.0.0.1:3306/test", max_overflow=5)

Base = declarative_base()

class Host(Base):
    __tablename__ = 'host1'
    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("group1.id"))  #主机关联组id
    #表示在group表中可以通过host_list查看host表内容，在host表中可以通过group查看group表内容
    group = relationship("Group", backref="host") 
    #group_list = relationship("Group",back_populates="host_list") #使用populates两边名称要一致

class Group(Base):
    __tablename__ = "group1"
    id = Column(Integer, primary_key=True)
    name = Column(String(64),unique=True, nullable=False)
    #host_id = Column(Integer, ForeignKey("hosts.id")) #创建一个组就要指定一个主机id变成一对一的关系
    #host_list = relationship("Host",back_populates="group_list") #使用populates两边名称要一致,两个表对应设置名称group_list和host_list

#Base.metadata.create_all(engine) #构建表

if __name__ == "__main__":
    SessionCls = sessionmaker(bind=engine)
    session = SessionCls()
    #建组
    g1 = Group(name="g1")
    g2 = Group(name="g2")
    g3 = Group(name="g3")
　　#建主机,关联组
    h1 = Host(hostname="localhost1", ip_addr="127.0.0.1",group_id="1")
    h2 = Host(hostname="web2", ip_addr="192.168.1.10",group_id="2")
    h3 = Host(hostname="agent2", ip_addr="192.168.1.20",group_id="3")
    session.add_all([g1, g2, g3])
    session.add_all([h1, h2, h3])
    session.commit()
    #两个表relationshap后，通过host表查询h1记录再通过group_id查找group表中对应的name
    h = session.query(Host).filter(Host.id == 1).first()
    print("h1:"h.group.name)
    session.commit()

映射关系

更多内容详见：http://www.xker.com/page/e2015/04/179550.html

多对多关系表，需要第三张表关联两张表

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

Base = declarative_base()

engine = create_engine("mysql+pymysql://root@127.0.0.1:3306/test", max_overflow=5, echo=True)

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)
                   )

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)
    groups = relationship("Group",
                          secondary=Host2Group,
                          backref="host_list")
    #用于显示查询结果
    def __repr__(self):
        return "<id=%s, hostame=%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) #创建数据结构

if __name__ == "__main__":
    SessionCls = sessionmaker(bind=engine)
    session = SessionCls()
　　
    #创建组
    #h1 = Host(hostname="localhost",ip_addr="127.0.0.1")
    #h2 = Host(hostname="roomsvr",ip_addr="10.10.10.10")
    #session.add(h1)
    #session.add_all([h1, h2])

    #创建主机
    #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()

    #组和主机关联
    groups = session.query(Group).all()
    g1 = session.query(Group).first()
    g2 = session.query(Group).filter(Group.name=="g2").first()
    h2 = session.query(Host).filter(Host.hostname=="localhost").first()
    h2.groups = groups #将主机同主机组关联
    #h2.groups.append(groups)
    session.commit()
    
    #关联表查询
    print("=====>",h2.groups)
    print("=====g1>",g1.host_list)
    print("=====g2>",g2.host_list)
    #h2.groups.pop()
    session.commit()

join

几个Join的区别 http://stackoverflow.com/questions/38549/difference-between-inner-and-outer-joins

left join(左联接) 返回包括左表中的所有记录和右表中交集的记录
right join(右联接) 返回包括右表中的所有记录和左表中交集的记录
inner join(等值连接) 只返回两个表中的交集字段

    #join 接上例代码

    objs = session.query(Host).join(Host.groups).group_by(Group.name).all()#取两个表的交集，按组名排序

    #SELECT * FROM host INNER JOIN host_2_group ON host.id = host_2_group.host_id
    #INNER JOIN `group` ON `group`.id = host_2_group.group_id GROUP BY `group`.id
    
    #count

    objs = session.query(Host, func.count(Host.hostname)).group_by(Host.id).all()

    #SELECT * count(host.hostname) FROM host GROUP BY host.id
    
    objs = session.query(Host,func.count(Group.name)).
        join(Host.groups).group_by(Group.name).all()

    #SELECT host.id,host.hostname,host.ip_addr,host.port,count(`group`.name) as count_1 FROM host
    #INNER JOIN host_2_group  ON host.id = host_2_group.host_id INNER JOIN `group` ON `group`.id = 
    #host_2_group.group_id GROUP BY `group`.name

    #print(objs)
    session.commit()

更多ORM内容:

http://files.cnblogs.com/files/wupeiqi/sqlalchemy.pdf.zip