Python Sqlalchemy

Posted 2020-07-02 善恶美丑

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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

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,执行原生的SQL，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 -*-
  
from sqlalchemy import create_engine
  
  
engine = create_engine("mysql+mysqldb://root:123@127.0.0.1:3306/s11", max_overflow=5)
  
engine.execute(
    "INSERT INTO ts_test (a, b) VALUES (\'2\', \'v1\')"
)
  
engine.execute(
     "INSERT INTO ts_test (a, b) VALUES (%s, %s)",
    ((555, "v1"),(666, "v1"),)
)
engine.execute(
    "INSERT INTO ts_test (a, b) VALUES (%(id)s, %(name)s)",
    id=999, name="v1"
)
  
result = engine.execute(\'select * from ts_test\')
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。

#!/usr/bin/env python
# -*- coding:utf-8 -*-
 
from sqlalchemy import create_engine, Table, Column, Integer, String, MetaData, ForeignKey
 
metadata = MetaData() # metadata 作用：绑定创建的表对象，进行create_all创建
 
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+mysqldb://root@localhost:3306/test", max_overflow=5) # max_overflow 指定最大连接数
 
metadata.create_all(engine)

一个完整的创建库和插入数据的例子

from sqlalchemy import create_engine,and_,or_
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+mysqldb://root@localhost:3306/test",echo=False)
 
 
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=\'ubuntu\',ip_addr=\'192.168.2.243\',port=20000)
    #h3 = Host(hostname=\'ubuntu2\',ip_addr=\'192.168.2.244\',port=20000)
    #session.add(h3)
    #session.add_all( [h1,h2])

　　　 #session.add_all([
　　　 #　　Host(hostname="aa",ip_addr="192.168.1.11"),
　　　 #　　Host(hostname="bb",ip_addr="192.168.1.12")]
　　　 #　　)
　　　 # session.commit()



    #h2.hostname = \'ubuntu_test\' #只要没提交,此时修改也没问题
    #session.rollback()
    #session.commit() #提交

注意：sqlalchemy 存在一些问题，当你新增一个字段时，sqlalchemy 无法自动增加字段，因为表已经存在了他就不会再做操作，解决办法1：删除表，重新创建（sqlalchemy有一个开源的工具可以自动增加字段，需要单独安装）。。解决办法2：使用原生的sql进行操作，

查询

#查询

#简单查询
    res = session.query(Host).filter(Host.hostname=="ubuntu").first()#取一条数据
    print(res.hostname)
    # session.delete(res) #查询的结果可以删除
    # res.hostname="ubuntu2"  #也可以修改
    #session.commit()
    res = session.query(Host).filter(Host.id > 1).all()#取多条数据
for i in res:print i.hostname

#高级查询
# ret=session.query(Users).filter(Users.id > 2).first()
    # print(ret.groupname)#指定为first显示为这样显示
    # ret=session.query(Users).filter(Users.id > 2).all()
    # for i in ret:print(i.groupname) # 指定为返回的是一个列表，列表里包含类
    # ret=session.query(Users).filter_by(groupname="g1").all()#过滤器类型为filter_by时,可以过滤一些关键字
    # print(ret.groupname)#
    # for i in ret:print(i.groupname)
    # ret = session.query(Users).filter(Users.groupname.in_(["g1","g2"])).all()#.in_表示包含在后面的列表里的值
    # for i in ret:print(i.groupname)
    # ret = session.query(Users.groupname.label("wocao")).all()#label表示将表中的字段起一个别名
    # print (ret,type(ret))
    # ret = session.query(Users).order_by(Users.groupname).all()# order_by 排序，在此表示对Users下的groupname字段排序
    # for i in ret:print(i.groupname)
    # ret = session.query(Users).filter(Users.id > 1).order_by(Users.groupname).all()#order_by 排序，在此表示对Users下的id字段大于2的groupname排序
    # for i in ret:print(i.groupname)
    # ret = session.query(Users).filter(Users.id > 1).order_by(Users.groupname)[1:3]#order_by 排序，在此表示对Users下的id字段大于2的groupname排序,进行切片操作，获取第1个和第2个的值
    # for i in ret:print(i.groupname)
# use and_() 需要导入and_模块
ret = session.query(Host).filter(and_(Host.hostname.like("ub%"),Host.port >20)).all()
    for i in ret:print(i.hostname)
# or_()
from sqlalchemy import or_
    ret = session.query(Host).filter(or_(Host.hostname==\'ubunt\',Host.port==22)).all()
    for i in ret:print(i.hostname)

修改

 #修改
    session.query(Host).filter(Host.id > 4).update({"groupname":"g1"})
    session.commit()

删除

    #删除
    session.query(Host).filter(Host.id >4).delete()
    session.commit()

外键关联

A one to many relationship places a foreign key on the child table referencing the parent.relationship() is then specified on the parent, as referencing a collection of items represented by the child

from sqlalchemy import Table, Column, Integer, ForeignKey
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base

首先来看看什么是外键，为什么要有外键

实例：一对多

import pymysql
from sqlalchemy import create_engine,MetaData,ForeignKey,and_,or_
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String
from  sqlalchemy.orm import sessionmaker,relationship
# 生成一个sqlorm基类
Base = declarative_base()
#创建一个引擎
engine = create_engine("mysql+pymysql://root:chen27@localhost:3306/chen",echo=False)

class Hosts(Base):
    __tablename__=\'hosts\'
    id = Column(Integer,primary_key=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(\'groups.id\')) # 外键关联groups下的id
    group = relationship("Groups") # 关联查询时候用，表示在Hosts表里通过什么字段(group)可以调用groups表（这里是表的类名Groups）里的字段信息 【其实就相当于反射，把Groups类的内存地址反射给group，从而获取到Groups下的所有字段，这个过程等同于实例化】
class Groups(Base):
    __tablename__=\'groups\'
    id = Column(Integer,primary_key=True)
    groupname = Column(String(64),unique=True,nullable=False)
Base.metadata.create_all(engine)

if __name__ == "__main__":
    sess = sessionmaker(bind=engine)
    session = sess()
    # g1 = Groups(groupname = "g1")
    # g2 = Groups(groupname = "g2")
    # g3 = Groups(groupname = "g3")
    # h1 = Hosts(hostname="h1",ip_addr="192.168.1.10",group_id="1")
    # h2 = Hosts(hostname="h2",ip_addr="192.168.1.11",group_id="2")
    #
    # session.add_all([h1,h2,g1,g2,g3])
    # session.commit()
    h1 = session.query(Hosts).filter(Hosts.hostname=="h1").first() # 查询主机对应的组
    print(h1.group.groupname) # 查询的时候group必须与字段指定的group字段一致 才能找到Groups类，获取到相对应的字段信息

上面的例子加入了关联查询的实例，通过主机查询对应的组，那我们如果想要通过组获取组下对应的主机呢？上面肯定是没法实现的，那么来看下面（在Groups下面也添加一个关联字段）

import pymysql
from sqlalchemy import create_engine,MetaData,ForeignKey,and_,or_
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String
from  sqlalchemy.orm import sessionmaker,relationship
# 生成一个sqlorm基类
Base = declarative_base()
#创建一个引擎
engine = create_engine("mysql+pymysql://root:chen27@localhost:3306/chen",echo=False)

class Hosts(Base):
    __tablename__=\'hosts\'
    id = Column(Integer,primary_key=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(\'groups.id\')) # 外键关联groups下的id
    group = relationship("Groups") # 关联查询时候用，表示在Hosts表里通过什么字段(group)可以调用groups表（这里是表的类名Groups）里的字段信息
class Groups(Base):
    __tablename__=\'groups\'
    id = Column(Integer,primary_key=True)
    groupname = Column(String(64),unique=True,nullable=False)
    hosts = relationship("Hosts") # Groups也添加一个关联查询的字段
Base.metadata.create_all(engine)

if __name__ == "__main__":
    sess = sessionmaker(bind=engine)
    session = sess()
    # g1 = Groups(groupname = "g1")
    # g2 = Groups(groupname = "g2")
    # g3 = Groups(groupname = "g3")
    # h1 = Hosts(hostname="h1",ip_addr="192.168.1.10",group_id="1")
    # h2 = Hosts(hostname="h2",ip_addr="192.168.1.11",group_id="2")
    #
    # session.add_all([h1,h2,g1,g2,g3])
    # session.commit()
    # h1 = session.query(Hosts).filter(Hosts.hostname=="h1").first()
    # print(h1.group.groupname)
    # h3 = Hosts(hostname="h3",ip_addr="192.168.1.12",group_id="1") # 新加了一条主机h3属于g1组
    # session.add(h3)
    # session.commit()
    g1 = session.query(Groups).filter(Groups.groupname=="g1").first() # 查询主机组下面包含了几个主机，
    print(g1.hosts)
    #[<__main__.Hosts object at 0x7ffb945af5f8>, <__main__.Hosts object at 0x7ffb945af668>]

上面又在groups下面添加了一个relationship，对应Hosts类，还有一个比较简单的方法，直接在Host类下面做一个反向关联，需要额外导入一个模块backref

import pymysql
from sqlalchemy import create_engine,MetaData,ForeignKey,and_,or_
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String
from  sqlalchemy.orm import sessionmaker,relationship,backref#反向关联模块
# 生成一个sqlorm基类
Base = declarative_base()
#创建一个引擎
engine = create_engine("mysql+pymysql://root:chen27@localhost:3306/chen",echo=False)

class Hosts(Base):
    __tablename__=\'hosts\'
    id = Column(Integer,primary_key=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(\'groups.id\')) # 外键关联groups下的id
    group = relationship("Groups",backref=\'hosts_list\') # backref表示反向关联hosts_list可以指定任意字符串，但是你调用的时候必须一致
class Groups(Base):
    __tablename__=\'groups\'
    id = Column(Integer,primary_key=True)
    groupname = Column(String(64),unique=True,nullable=False)
    # hosts = relationship("Hosts")
Base.metadata.create_all(engine)

if __name__ == "__main__":
    sess = sessionmaker(bind=engine)
    session = sess()
    # g1 = Groups(groupname = "g1")
    # g2 = Groups(groupname = "g2")
    # g3 = Groups(groupname = "g3")
    # h1 = Hosts(hostname="h1",ip_addr="192.168.1.10",group_id="1")
    # h2 = Hosts(hostname="h2",ip_addr="192.168.1.11",group_id="2")
    #
    # session.add_all([h1,h2,g1,g2,g3])
    # session.commit()
    # h1 = session.query(Hosts).filter(Hosts.hostname=="h1").first()
    # print(h1.group.groupname)
    # h3 = Hosts(hostname="h3",ip_addr="192.168.1.12",group_id="1")
    # session.add(h3)
    # session.commit()
    g1 = session.query(Groups).filter(Groups.groupname=="g1").first()
    print(g1.hosts_list)#这里的hosts_list必须与刚才反向关联的一致
    for i in g1.hosts_list:print(i.hostname)
    #[<__main__.Hosts object at 0x7f8553ca2668>, <__main__.Hosts object at 0x7f8553ca26d8>]
    #　　h1  h3

附，原生sql join查询

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

INNER JOIN: Returns all rows when there is at least one match in BOTH tables
LEFT JOIN: Return all rows from the left table, and the matched rows from the right table
RIGHT JOIN: Return all rows from the right table, and the matched rows from the left table

inner join sql

select * from hosts inner join groups on hosts.group_id = groups.id;
+----+----------+--------------+------+----------+----+-----------+
| id | hostname | ip_addr      | port | group_id | id | groupname |
+----+----------+--------------+------+----------+----+-----------+
|  2 | h1       | 192.168.1.10 |   22 |        1 |  1 | g1        |
|  3 | h2       | 192.168.1.11 |   22 |        2 |  2 | g2        |
|  4 | h3       | 192.168.1.12 |   22 |        1 |  1 | g1        |
+----+----------+--------------+------+----------+----+-----------+

inner join sqlalchemy

    ret = session.query(Hosts).join(Hosts.group).filter(Groups.groupname=="g1").all() # query(表的类) .join(关联查询的字段)
    for i in ret:print(i.hostname)
    print(len(ret))
\'\'\'
h1
h3
2
\'\'\'

left join sql

#首先我们先插入一个数据 以便看到效果
mysql> insert into hosts(hostname,ip_addr) values("h4","192.168.1.13");
Query OK, 1 row affected (0.01 sec)

mysql> select * from hosts;
+----+----------+--------------+------+----------+
| id | hostname | ip_addr      | port | group_id |
+----+----------+--------------+------+----------+
|  2 | h1       | 192.168.1.10 |   22 |        1 |
|  3 | h2       | 192.168.1.11 |   22 |        2 |
|  4 | h3       | 192.168.1.12 |   22 |        1 |
|  6 | h4       | 192.168.1.13 | NULL |     NULL |
+----+----------+--------------+------+----------+


#left joiin sql
mysql> select * from hosts left join groups on hosts.group_id = groups.id;
+----+----------+--------------+------+----------+------+-----------+
| id | hostname | ip_addr      | port | group_id | id   | groupname |
+----+----------+--------------+------+----------+------+-----------+
|  2 | h1       | 192.168.1.10 |   22 |        1 |    1 | g1        |
|  3 | h2       | 192.168.1.11 |   22 |        2 |    2 | g2        |
|  4 | h3       | 192.168.1.12 |   22 |        1 |    1 | g1        |
|  6 | h4       | 192.168.1.13 | NULL |     NULL | NULL | NULL      |
+----+----------+--------------+------+----------+------+-----------+
4 rows in set (0.00 sec)

right join sql

mysql> select * from hosts right join groups on hosts.group_id = groups.id;
+------+----------+--------------+------+----------+----+-----------+
| id   | hostname | ip_addr      | port | group_id | id | groupname |
+------+----------+--------------+------+----------+----+-----------+
|    2 | h1       | 192.168.1.10 |   22 |        1 |  1 | g1        |
|    3 | h2       | 192.168.1.11 |   22 |        2 |  2 | g2        |
|    4 | h3       | 192.168.1.12 |   22 |        1 |  1 | g1        |
| NULL | NULL     | NULL         | NULL |     NULL |  3 | g3        |
+------+----------+--------------+------+----------+----+-----------+

full join （因mysql不支持full join 只能通过union的替代方法实现）

mysql> select * from hosts left join groups on hosts.group_id = groups.id union select * from hosts right join groups on hosts.group_id = groups.id;
+------+----------+--------------+------+----------+------+-----------+
| id   | hostname | ip_addr      | port | group_id | id   | groupname |
+------+----------+--------------+------+----------+------+-----------+
|    2 | h1       | 192.168.1.10 |   22 |        1 |    1 | g1        |
|    3 | h2       | 192.168.1.11 |   22 |        2 |    2 | g2        |
|    4 | h3       | 192.168.1.12 |   22 |        1 |    1 | g1        |
|    6 | h4       | 192.168.1.13 | NULL |     NULL | NULL | NULL      |
| NULL | NULL     | NULL         | NULL |     NULL |    3 | g3        |
+------+----------+--------------+------+----------+------+-----------+

group by sql过滤重复的字段（分类聚合）

mysql> select * from hosts;
+----+----------+--------------+------+----------+
| id | hostname | ip_addr      | port | group_id |
+----+----------+--------------+------+----------+
|  1 | h1       | 192.168.1.10 |   22 |        1 |
|  2 | h2       | 192.168.1.11 |   22 |        2 |
|  3 | h3       | 192.168.1.12 |   22 |        1 |
+----+----------+--------------+------+----------+
3 rows in set (0.00 sec)

mysql> select * from hosts group by group_id;
+----+----------+--------------+------+----------+
| id | hostname | ip_addr      | port | group_id |
+----+----------+--------------+------+----------+
|  1 | h1       | 192.168.1.10 |   22 |        1 |
|  2 | h2       | 192.168.1.11 |   22 |        2 |
+----+----------+--------------+------+----------+
2 rows in set (0.00 sec)

------------------------------------------------------------------------
mysql> select * from hosts right join groups on hosts.group_id = groups.id;    
+------+----------+--------------+------+----------+----+-----------+
| id   | hostname | ip_addr      | port | group_id | id | groupname |
+------+----------+--------------+------+----------+----+-----------+
|    1 | h1       | 192.168.1.10 |   22 |        1 |  1 | g1        |
|    2 | h2       | 192.168.1.11 |   22 |        2 |  2 | g2        |
|    3 | h3       | 192.168.1.12 |   22 |        1 |  1 | g1        |
| NULL | NULL     | NULL         | NULL |     NULL |  3 | g3        |
+------+----------+--------------+------+----------+----+-----------+
4 rows in set (0.00 sec)

mysql> select * from hosts right join groups on hosts.group_id = groups.id group by groupname;
+------+----------+--------------+------+----------+----+-----------+
| id   | hostname | ip_addr      | port | group_id | id | groupname |
+------+----------+--------------+------+----------+----+-----------+
|    1 | h1       | 192.168.1.10 |   22 |        1 |  1 | g1        |
|    2 | h2       | 192.168.1.11 |   22 |        2 |  2 | g2        |
| NULL | NULL     | NULL         | NULL |     NULL |  3 | g3        |
+------+----------+--------------+------+----------+----+-----------+
3 rows in set (0.00 sec)

mysql> select count(*),groups.groupname from hosts inner join groups on hosts.group_id = groups.id group by groups.groupname;
+----------+-----------+
| count(*) | groupname |
+----------+-----------+
| 2 | g1 |
| 1 | g2 |
+----------+-----------+
2 rows in set (0.00 sec)

group by sqlalchemy

    ret = session.query(Hosts,func.count(Groups.groupname)).join(Hosts.group).group_by(Groups.groupname).all()
    print(ret)

上述的情况是一个组对应多个主机，那如果一个主机想要对应多个组呢？上述的表结构就无法实现了

many to many 多对多

1、

# 多对多
# 1、创建另一个表 与hosts和groups表相关联
Hosts_2_Groups = Table(\'Hosts_2_Groups\',Base.metadata,
    # Column(\'id\',nullable=False,autoincrement=True),
    Column(\'host_id\',ForeignKey(\'hosts.id\'),primary_key=True),
    Column(\'group_id\',ForeignKey(\'groups.id\'),primary_key=True),
)
class Hosts(Base):
    __tablename__=\'hosts\'
    id = Column(Integer,primary_key=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(\'groups.id\')) #这里外键关联到groups就取消了，
    group = relationship("Groups",backref="hosts_list",secondary=Hosts_2_Groups) #secondary指定中间表的实例
    def __repr__(self): # 返回一些信息
        return "<id=%s,hostname=%s,ip_addr=%s>" %(self.id,
                                                  self.hostname,
                                                  self.ip_addr)
class Groups(Base):
    __tablename__=\'groups\'
    id = Column(Integer,primary_key=True)
    groupname = Column(String(64),unique=True,nullable=False)
    def __repr__(self):
        return "id=%s,groupname=%s"%(self.id,self.groupname)
Base.metadata.create_all(engine)

2、插入数据

    sess = sessionmaker(bind=engine)
    session = sess()
    # g1 = Groups(groupname = "g1")
    # g2 = Groups(groupname = "g2")
    # g3 = Groups(groupname = "g3")
    # g4 = Groups(groupname = "g4")
    # h1 = Hosts(hostname="h1",ip_addr="192.168.1.10")
    # h2 = Hosts(hostname="h2",ip_addr="192.168.1.11")
    # h3 = Hosts(hostname="h3",ip_addr="192.168.1.12")
    # #
    # session.add_all([h1,h2,h3,g1,g2,g3,g4])
    # session.commit()

3、关联第三张表（你也可以直接在插入数据的时候指定组，例如：

\'\'\'
g1 = Groups(groupname = "g1"
 h1 = Hosts(hostname="h1",ip_addr="192.168.1.10"
h1.group = [g1,g2,g3...])
)
）
\'\'\'

    # h1 = session.query(Hosts).filter(Hosts.hostname=="h2").first()
    # groups = session.query(Groups).all()
    # h1.group= groups
    # session.commit()

4、查询

# 查询组对应的主机
g2 = session.query(Groups).filter(Groups.groupname=="g2").first()
    print(g2.hosts_list)
>>>[<id=1,hostname=h1,ip_addr=192.168.1.10>, <id=2,hostname=h2,ip_addr=192.168.1.11>]

#查询主机对应的组
    h1 = session.query(Hosts).filter(Hosts.hostname=="h1").first()
    print(h1.group)
>>>
[id=1,groupname=g1, id=2,groupname=g2, id=3,groupname=g3]

更多ORM内容点击这里 http://119.90.25.39/files.cnblogs.com/files/wupeiqi/sqlalchemy.pdf.zip

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