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

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。

#!/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)

#创建一个ts_test表

engine.execute("create TABLE ts_test(a VARCHAR(100) ,b VARCHAR(100))")

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()

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)

metadata.create_all(engine)

增删改查

#!/usr/bin/env python

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

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+mysqldb://root:123@127.0.0.1:3306/s11", 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'})

conn.close()

#增数据

# sql = user.insert().values(id=123, name='wu')

# conn.execute(sql)

# conn.close()

#删除数据

# 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, ])

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

# 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)

# result = conn.execute(sql)

# print result.fetchall()

# conn.close()

一个简单的完整例子

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+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])

#h2.hostname = 'ubuntu_test' #只要没提交,此时修改也没问题

#session.rollback()

#session.commit() #提交

res = session.query(Host).filter(Host.hostname.in_(['ubuntu2','localhost'])).all()

print(res)

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。

#!/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:123@127.0.0.1:3306/s11", 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='sb')

# session.add(u)

# session.add_all([

# User(id=3, name='sb'),

# User(id=4, name='sb')

# ])

# 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='sb').first()

# ret = session.query(User).filter_by(name='sb').all()

# print ret

# ret = session.query(User).filter(User.name.in_(['sb','bb'])).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()

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

Base = declarative_base()

class Parent(Base):

__tablename__ = 'parent'

id = Column(Integer, primary_key=True)

children = relationship("Child")

class Child(Base):

__tablename__ = 'child'

id = Column(Integer, primary_key=True)

parent_id = Column(Integer, ForeignKey('parent.id’))

To establish a bidirectional relationship in one-to-many, where the “reverse” side is a many to one, specify an additional relationship() and connect the two using therelationship.back_populates parameter:

class Parent(Base):

__tablename__ = 'parent'

id = Column(Integer, primary_key=True)

children = relationship("Child", back_populates="parent")

class Child(Base):

__tablename__ = 'child'

id = Column(Integer, primary_key=True)

parent_id = Column(Integer, ForeignKey('parent.id'))

parent = relationship("Parent", back_populates="children”)

Child will get a parent attribute with many-to-one semantics.

Alternatively, the backref option may be used on a single relationship() instead of usingback_populates:

class Parent(Base):

__tablename__ = 'parent'

id = Column(Integer, primary_key=True)

children = relationship("Child", backref="parent”)

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

select host.id,hostname,ip_addr,port,host_group.name from host right join host_group on host.id = host_group.host_id

in SQLAchemy

session.query(Host).join(Host.host_groups).filter(HostGroup.name=='t1').group_by("Host").all()

group by 查询

select name,count(host.id) as NumberOfHosts from host right join host_group on host.id= host_group.host_id group by name;

in SQLAchemy

from sqlalchemy import func

session.query(HostGroup, func.count(HostGroup.name )).group_by(HostGroup.name).all()

#another example

session.query(func.count(User.name), User.name).group_by(User.name).all() SELECT count(users.name) AS count_1, users.name AS users_name

FROM users GROUP BY users.name

文档采用：http://www.cnblogs.com/alex3714/articles/5248247.html

转载于:https://www.cnblogs.com/TaleG/p/6686951.html

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