SQLAlchemy

一 介绍

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。

1. 安装：

pip3 install sqlalchemy

2. 框架与流程

组成部分：

• Engine，框架的引擎
• Connection Pooling ，数据库连接池
• Dialect，选择连接数据库的DB API种类
• Schema/Types，架构和类型
• SQL Exprression Language，SQL表达式语言

流程：

#1、使用者通过ORM对象提交命令
#2、将命令交给SQLAlchemy Core（Schema/Types  SQL Expression Language）转换成SQL
#3、使用 Engine/ConnectionPooling/Dialect 进行数据库操作
#3.1、匹配使用者事先配置好的egine
#3.2、egine从连接池中取出一个链接
#3.3、基于该链接通过Dialect调用DB API，将SQL转交给它去执行

上述流程分析，可以大致分为两个阶段

#第一个阶段（流程1-2）：将SQLAlchemy的对象换成可执行的sql语句

#第二个阶段（流程3）：将sql语句交给数据库执行

SQLAlchemy本身无法操作数据库，其必须以来pymsql等第三方插件，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：http://docs.sqlalchemy.org/en/latest/dialects/index.html

　　

二 使用

执行原生SQL语句

from sqlalchemy import create_engine

#1 准备
# 需要事先安装好pymysql
# 需要事先创建好数据库:create database db1 charset utf8;

#2 创建引擎
engine = create_engine(
    "mysql+pymysql://root:123@127.0.0.1:3306/t1?charset=utf8",
    max_overflow=0,  # 超过连接池大小外最多创建的连接
    pool_size=5,  # 连接池大小
    pool_timeout=30,  # 池中没有线程最多等待的时间，否则报错
    pool_recycle=-1  # 多久之后对线程池中的线程进行一次连接的回收（重置）
)

#3 执行sql
# egine.execute('create table if not EXISTS t1(id int PRIMARY KEY auto_increment,name char(32));')

# cur=egine.execute('insert into t1 values(%s,%s);',[(1,"zhou"),(2,"jun"),(3,"egon3")]) #按位置传值

# cur=egine.execute('insert into t1 values(%(id)s,%(name)s);',name='hao',id=4) #按关键字传值

#4 新插入行的自增id
# print(cur.lastrowid)

#5 查询
cur=egine.execute('select * from t1')

cur.fetchone() #获取一行
cur.fetchmany(2) #获取多行
cur.fetchall() #获取所有行

#############
def task(arg):
    conn = engine.raw_connection()
    cursor = conn.cursor()
    cursor.execute(
        "select * from t1"
    )
    result = cursor.fetchall()
    cursor.close()
    conn.close()
 
 
for i in range(20):
    t = threading.Thread(target=task, args=(i,))
    t.start()


############
def task(arg):
    conn = engine.contextual_connect()
    with conn:
        cur = conn.execute(
            "select * from t1"
        )
        result = cur.fetchall()
        print(result)


for i in range(20):
    t = threading.Thread(target=task, args=(i,))
    t.start()

注意: 查看连接 show status like 'Threads%';　　

创建表

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import datetime
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, Text, ForeignKey, DateTime, UniqueConstraint, Index

Base = declarative_base()


class Users(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    name = Column(String(32), index=True, nullable=False) #nullable为False是不允许为空
    # email = Column(String(32), unique=True)
    # ctime = Column(DateTime, default=datetime.datetime.now)
    # extra = Column(Text, nullable=True)

    __table_args__ = (
        # 联合唯一索引
        # UniqueConstraint('id', 'name', name='uix_id_name'),
        # 联合索引
        # Index('ix_id_name', 'name', 'email'),
           'mysql_engine': 'InnoDB', #指定存储引擎
           'mysql_charset': 'utf8'  #指定表的字符编码

    )


def init_db():
    """
    根据类创建数据库表
    :return: 
    """
    engine = create_engine(
        "mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8",
        max_overflow=0,  # 超过连接池大小外最多创建的连接
        pool_size=5,  # 连接池大小
        pool_timeout=30,  # 池中没有线程最多等待的时间，否则报错
        pool_recycle=-1  # 多久之后对线程池中的线程进行一次连接的回收（重置）
    )

    Base.metadata.create_all(engine)


def drop_db():
    """
    根据类删除数据库表
    :return: 
    """
    engine = create_engine(
        "mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8",
        max_overflow=0,  # 超过连接池大小外最多创建的连接
        pool_size=5,  # 连接池大小
        pool_timeout=30,  # 池中没有线程最多等待的时间，否则报错
        pool_recycle=-1  # 多久之后对线程池中的线程进行一次连接的回收（重置）
    )

    Base.metadata.drop_all(engine)


if __name__ == '__main__':
    #drop_db()
    init_db()

    

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import datetime
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, Text, ForeignKey, DateTime, UniqueConstraint, Index
from sqlalchemy.orm import relationship

Base = declarative_base()


# ##################### 一对多示例 #########################
class Hobby(Base):
    __tablename__ = 'hobby'
    id = Column(Integer, primary_key=True)
    caption = Column(String(50), default='篮球')


class Person(Base):
    __tablename__ = 'person'
    nid = Column(Integer, primary_key=True)
    name = Column(String(32), index=True, nullable=True)
    hobby_id = Column(Integer, ForeignKey("hobby.id"))

    # 与生成表结构无关，仅用于查询方便
    hobby = relationship("Hobby", backref='pers')


# ##################### 多对多示例 #########################

class Server2Group(Base):
    __tablename__ = 'server2group'
    id = Column(Integer, primary_key=True, autoincrement=True)
    server_id = Column(Integer, ForeignKey('server.id'))
    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)

    # 与生成表结构无关，仅用于查询方便
    servers = relationship('Server', secondary='server2group', backref='groups')


class Server(Base):
    __tablename__ = 'server'

    id = Column(Integer, primary_key=True, autoincrement=True)
    hostname = Column(String(64), unique=True, nullable=False)

执行数据库操作

#!/usr/bin/env python
# -*- coding:utf-8 -*-
from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from models import Users
  
engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)
  
# 每次执行数据库操作时，都需要创建一个session
session = Session()
  
# ############# 执行ORM操作 #############
obj1 = Users(name="alex1")
session.add(obj1)
  
# 提交事务
session.commit()
# 关闭session
session.close()

基本的增删改查

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import time
import threading

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy import create_engine
from sqlalchemy.sql import text

from db import Users, Hosts

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/demo1", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)

session = Session()

# ################ 添加 ################
"""
obj1 = Users(name="wupeiqi")
session.add(obj1)

session.add_all([
    Users(name="wupeiqi"),
    Users(name="alex"),
    Hosts(name="c1.com"),
])
session.commit()
"""

# ################ 删除 ################
"""
session.query(Users).filter(Users.id > 2).delete()
session.commit()
"""
# ################ 修改 ################
"""
session.query(Users).filter(Users.id > 0).update({"name" : "099"})
session.query(Users).filter(Users.id > 0).update({Users.name: Users.name + "099"}, synchronize_session=False) #非运算操作指定synchronize_session=False
session.query(Users).filter(Users.id > 0).update({"age": Users.age + 1}, synchronize_session="evaluate")# 运算操作时指定参数为synchronize_session="evaluate"
session.commit()
"""
# ################ 查询 ################
"""
r1 = session.query(Users).all() # 查所有
r2 = session.query(Users.name.label('xx'), Users.age).all() #查指定字段
r3 = session.query(Users).filter(Users.name == "alex").all() # 值过滤
r4 = session.query(Users).filter_by(name='alex').all() # 属性过滤
r5 = session.query(Users).filter_by(name='alex').first() # 取结果的第一个
r6 = session.query(Users).filter(text("id<:value and name=:name")).params(value=224, name='fred').order_by(Users.id).all()
r7 = session.query(Users).from_statement(text("SELECT * FROM users where name=:name")).params(name='ed').all()
"""


session.close()

#!/usr/bin/env python
# -*- coding:utf-8 -*-
from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session
from models import Users

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)

"""
# 线程安全，基于本地线程实现每个线程用同一个session
# 特殊的：scoped_session中有原来方法的Session中的一下方法：

public_methods = (
    '__contains__', '__iter__', 'add', 'add_all', 'begin', 'begin_nested',
    'close', 'commit', 'connection', 'delete', 'execute', 'expire',
    'expire_all', 'expunge', 'expunge_all', 'flush', 'get_bind',
    'is_modified', 'bulk_save_objects', 'bulk_insert_mappings',
    'bulk_update_mappings',
    'merge', 'query', 'refresh', 'rollback',
    'scalar'
)
"""
session = scoped_session(Session)


# ############# 执行ORM操作 #############
obj1 = Users(name="alex1")
session.add(obj1)



# 提交事务
session.commit()
# 关闭session
session.close()

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import time
import threading

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy import create_engine
from db import Users

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)


def task(arg):
    session = Session()

    obj1 = Users(name="alex1")
    session.add(obj1)

    session.commit()


for i in range(10):
    t = threading.Thread(target=task, args=(i,))
    t.start()

常用操作

#　条件
ret = session.query(Users).filter_by(name='alex').all()
ret = session.query(Users).filter(Users.id > 1, Users.name == 'eric').all()

# 在什么到什么之间
ret = session.query(Users).filter(Users.id.between(1, 3), Users.name == 'eric').all()

# in 与 notin
ret = session.query(Users).filter(Users.id.in_([1,3,4])).all()
ret = session.query(Users).filter(~Users.id.in_([1,3,4])).all()
ret = 
session.query(Users).filter(Users.id.in_(session.query(Users.id).filter_by(name='eric'))).all()

# and 与 or
from sqlalchemy import and_, or_
ret = session.query(Users).filter(and_(Users.id > 3, Users.name == 'eric')).all()
ret = session.query(Users).filter(or_(Users.id < 2, Users.name == 'eric')).all()
ret = session.query(Users).filter(
    or_(
        Users.id < 2,
        and_(Users.name == 'eric', Users.id > 3),
        Users.extra != ""
    )).all()


# 通配符
ret = session.query(Users).filter(Users.name.like('e%')).all() # e开头对所有
ret = session.query(Users).filter(~Users.name.like('e%')).all() # ～取反

# 限制
ret = session.query(Users)[1:2:1]  #对结果切片

# 排序
# desc降序，asc升序
ret = session.query(Users).order_by(Users.name.desc()).all()
ret = session.query(Users).order_by(Users.name.desc(), Users.id.asc()).all()

# 分组
from sqlalchemy.sql import func

ret = session.query(Users).group_by(Users.extra).all()
ret = session.query(
    func.max(Users.id),
    func.sum(Users.id),
    func.min(Users.id)).group_by(Users.name).all()

ret = session.query(
    func.max(Users.id),
    func.sum(Users.id),
    func.min(Users.id)).group_by(Users.name).having(func.min(Users.id) >2).all()

# 连表

ret = session.query(Users, Favor).filter(Users.id == Favor.nid).all()

ret = session.query(Person).join(Favor).all()

ret = session.query(Person).join(Favor, isouter=True).all()


# 组合  

# 把两次查询的结果组合到一个列表
q1 = session.query(Users.name).filter(Users.id > 2)
q2 = session.query(Favor.caption).filter(Favor.nid < 2)
ret = q1.union(q2).all()

q1 = session.query(Users.name).filter(Users.id > 2)
q2 = session.query(Favor.caption).filter(Favor.nid < 2)
ret = q1.union_all(q2).all()

　　

多对一查询及relationship反查

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import time
import threading

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy import create_engine
from sqlalchemy.sql import text
from sqlalchemy.engine.result import ResultProxy
from db import Users, Hosts, Hobby, Person

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)
session = Session()


# 使用relationship正向查询
"""
v = session.query(Person).first()
print(v.name)
print(v.hobby.caption) # 结果是一个对象
"""

# 使用relationship反向查询
"""
v = session.query(Hobby).first()
print(v.caption)
print(v.pers) # 结果是一个列表，列表内是关联的所有对象
"""

session.close()

　　

多对多查询及relationship反查

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import time
import threading

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy import create_engine
from sqlalchemy.sql import text
from sqlalchemy.engine.result import ResultProxy
from db import Users, Hosts, Hobby, Person, Group, Server, Server2Group

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)
session = Session()



# 使用relationship正向查询
"""
v = session.query(Group).first()
print(v.name)
print(v.servers) # 得到一个列表，里面是所有关联的对象
"""

# 使用relationship反向查询
"""
v = session.query(Server).first()
print(v.hostname)
print(v.groups)  # 得到一个列表，里面是所有关联的对象
"""


session.close()

子查询

#示例:查出id大于2的员工,当做子查询的表使用

#原生SQL:
# select * from (select * from emp where id > 2);

#ORM:
res=session.query(
    session.query(Emp).filter(Emp.id > 8).subquery()
).all()

#示例:#查出销售部门的员工姓名

#原生SQL:
# select ename from emp where dep_id in (select id from dep where dname='销售');

#ORM:
res=session.query(Emp.ename).filter(Emp.dep_id.in_(
    session.query(Dep.id).filter_by(dname='销售'), #传的是参数
    # session.query(Dep.id).filter(Dep.dname=='销售') #传的是表达式
)).all()

#示例:查询所有的员工姓名与部门名

#原生SQL:
# select ename as 员工姓名,(select dname from dep where id = emp.dep_id) as 部门名 from emp;

#ORM:
sub_sql=session.query(Dep.dname).filter(Dep.id==Emp.dep_id) #SELECT dep.dname FROM dep, emp WHERE dep.id = emp.dep_id
sub_sql.as_scalar() #as_scalar的功能就是把上面的sub_sql加上了括号

res=session.query(Emp.ename,sub_sql.as_scalar()).all()

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import time
import threading

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy import create_engine
from sqlalchemy.sql import text, func
from sqlalchemy.engine.result import ResultProxy
from db import Users, Hosts, Hobby, Person, Group, Server, Server2Group

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/demo?charset=utf8", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)
session = Session()

# 关联子查询
subqry = session.query(func.count(Server.id).label("sid")).filter(Server.id == Group.id).correlate(Group).as_scalar()
result = session.query(Group.name, subqry)
"""
SELECT `group`.name AS group_name, (SELECT count(server.id) AS sid 
FROM server 
WHERE server.id = `group`.id) AS anon_1 
FROM `group`
"""


# 原生SQL
"""
# 查询
cursor = session.execute('select * from users')
result = cursor.fetchall()

# 添加
cursor = session.execute('insert into users(name) values(:value)',params={"value":'wupeiqi'})
session.commit()
print(cursor.lastrowid)
"""

session.close()