SQLALchemy

SQLAlchemy是一个基于Python实现的ORM框架。该框架建立在 DB API之上，使用关系对象映射进行数据库操作 ，也就是将类和对象转换成SQL，然后使用数据API执行SQL并获取执行结果。

安装：pip3 install sqlalchemy

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

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

SQLALchemy，ORM框架

1、什么是orm框架
orm：对象关系映射
类   ---  表
对象 ---  一条记录
当有了对应关系之后，不需要再编写sql语句，直接操作，类，对象
2、sql vs orm
sql查询速度快，开发效率低
orm开发效率高，查询速度较低
3、概念理解
　　-db first      根据数据库的表生成类
　　-code first    根据类生成数据库的表
4、orm是怎么实现的
　　根据对象和类通过字符串格式化转化成sql语句
　　DDD中：unit of work 

使用原生sql语句

import time
import threading
import sqlalchemy
from sqlalchemy import create_engine
from sqlalchemy.engine.base import Engine
 
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）
)
 
 
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()

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import time
import threading
import sqlalchemy
from sqlalchemy import create_engine
from sqlalchemy.engine.base import Engine

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=0, pool_size=5)


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()

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import time
import threading
import sqlalchemy
from sqlalchemy import create_engine
from sqlalchemy.engine.base import Engine
from sqlalchemy.engine.result import ResultProxy
engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=0, pool_size=5)


def task(arg):
    cur = engine.execute("select * from t1")
    result = cur.fetchall()
    cur.close()
    print(result)


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

使用orm语句

创建数据库表

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, DateTime,ForeignKey,UniqueConstraint
from sqlalchemy import create_engine
from sqlalchemy.orm import relationship
import datetime

Base = declarative_base()

# 创建单表
class Classes(Base):
    __tablename__ = 'classes'
    id = Column(Integer, primary_key=True,autoincrement=True)
    name = Column(String(32))

class Student(Base):
    __tablename__="student"
    id =Column(Integer,primary_key=True,autoincrement=True)
    user=Column(String(32))
    pwd=Column(String(32))
    ctime=Column(DateTime,default=datetime.datetime.now)  #不要加()
    class_id=Column(Integer,ForeignKey("classes.id"))

    #不会生成字段，用于链表查询，backref用于反向链表查表
    cls = relationship("Classes", backref='stus')

class Hobby(Base):
    __tablename__="hobby"
    id=Column(Integer,primary_key=True,autoincrement=True)
    caption=Column(String(32),default="大球")

# 多对多关系   需要自检创建第三张表
class StudentToHobby(Base):
    __tablename__="studenttohobby"
    id = Column(Integer, primary_key=True, autoincrement=True)
    student_id=Column(Integer,ForeignKey('student.id'))
    hobby_id=Column(Integer,ForeignKey('hobby.id'))

    # 联合唯一
    __table_args__=(
        UniqueConstraint("student_id","hobby_id",name="uix_student_id_hobby_id"),
    )


def init_db():
    # 数据库连接相关
    engine = create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/s8sql?charset=utf8")
    # 创建表
    Base.metadata.create_all(engine)
def drop_db():
    engine = create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/s8sql?charset=utf8")
    # 删除表
    Base.metadata.drop_all(engine)

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

增

import models

from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine

# 连接数据库
engine=create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/s8sql?charset=utf8")
Session=sessionmaker(bind=engine)
# 每次执行数据库操作时，都需要创建一个session
session=Session()

# 添加单条数据
# obj=models.Classes(name="全栈8期")
# session.add(obj)

# 添加多条数据
# obj_all=[
#     models.Classes(name="全栈9期"),
#     models.Classes(name="全栈10期"),
#     models.Classes(name="全栈11期")
# ]
# session.add_all(obj_all)


# 添加数据（含有外键）
obj=models.Student(user="小花",pwd="123",class_id=2)
session.add(obj)

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

查

import models

from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine,text

# 连接数据库
engine=create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/s8sql?charset=utf8")
Session=sessionmaker(bind=engine)
# 每次执行数据库操作时，都需要创建一个session
session=Session()

# 查全部数据
# class_list=session.query(models.Classes).all()
# for classes in class_list:
#     print(classes.id,classes.name)

#别名查询
# class_list=session.query(models.Classes.id,models.Classes.name.label("xx")).all()
# for classes in class_list:
#     print(classes.id,classes.xx)

#条件查询  filter(条件)  filter_by()
# obj=session.query(models.Classes).filter(models.Classes.name=="全栈9期").all()
# for i in obj:
#     print(i.name)
# obj1=session.query(models.Classes).filter(models.Classes.name=="全栈9期").first()
# print(obj1.name)
# obj2=session.query(models.Classes).filter_by(name="全栈10期").first()
# print(obj2.name)

#子查询
# result = session.query(models.Classes).from_statement(text("SELECT * FROM classes where name=:name")).params(name='全栈11期').all()
# print(result)
# ret = session.query(models.Classes).filter(models.Classes.id.in_(session.query(models.Classes.id).filter_by(name='全栈8期'))).all()
# print(ret)

# 显示所有学生信息（含班级）
# 1、多次查询
# obj=session.query(models.Student).all()
# for obj in objs:
#     cls_obj = session.query(models.Classes).filter(models.Classes.id==obj.class_id).first()
#     print(obj.id,obj.username,obj.class_id,cls_obj.name)

# 2、连表查询   isouter=True mysql中leftjoin查询
# objs = session.query(models.Student.id,models.Student.user,models.Classes.name).join(models.Classes,isouter=True).all()
# print(objs)

# 3、使用relationship查询
# objs = session.query(models.Student).all()
# for item in objs:
#     print(item.id,item.user,item.class_id,item.cls.name)

#4、使用relationship反向查询    全栈9期所有的学生
# obj = session.query(models.Classes).filter(models.Classes.name=='全栈9期').first()
# student_list = obj.stus
# for item in student_list:
#     print(item.id,item.user)
# 提交事务
session.commit()
# 关闭session
session.close()

改

import models

from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine

# 连接数据库
engine=create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/s8sql?charset=utf8")
Session=sessionmaker(bind=engine)
# 每次执行数据库操作时，都需要创建一个session
session=Session()

# 改
# session.query(models.Classes).filter(models.Classes.id > 1).update({"name" : "099"})

# synchronize_session=False  字符串拼接
# session.query(models.Classes).filter(models.Classes.id > 0).update({models.Classes.name: models.Classes.name + "099"}, synchronize_session=False)

# synchronize_session="evaluate"  数字计算
session.query(models.Classes).filter(models.Classes.id > 0).update({"age": models.Classes.age + 1}, synchronize_session="evaluate")

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

删除

import models

from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine

# 连接数据库
engine=create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/s8sql?charset=utf8")
Session=sessionmaker(bind=engine)
# 每次执行数据库操作时，都需要创建一个session
session=Session()

# 删
session.query(models.Classes).filter(models.Classes.id > 2).delete()


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

 补充操作

#　条件
ret = session.query(Users).filter_by(name='alex').all()
ret = session.query(Users).filter(Users.id > 1, Users.name == 'eric').all() #并且关系
ret = session.query(Users).filter(Users.id.between(1, 3), Users.name == 'eric').all() #between区间
ret = session.query(Users).filter(Users.id.in_([1,3,4])).all()  #id=1or3or
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()

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()
ret = session.query(Users).filter(~Users.name.like('e%')).all()

# 限制 （mysql中的limit）
ret = session.query(Users)[1:2]

# 排序
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()  #inner join  一张表没有的，都不显示

ret = session.query(Person).join(Favor, isouter=True).all()  #left join   以左表为基准


# 组合
q1 = session.query(Users.name).filter(Users.id > 2)
q2 = session.query(Favor.caption).filter(Favor.nid < 2)
ret = q1.union(q2).all()  #数据重复，只留一条

q1 = session.query(Users.name).filter(Users.id > 2)
q2 = session.query(Favor.caption).filter(Favor.nid < 2)
ret = q1.union_all(q2).all()  #显示数据重复

数据库之间表的关系

增加数据和查询
            
            一对多：
                class UserType(Base):
                    __tablename__ = 'usertype'
                    id = Column(Integer, primary_key=True)
                    caption = Column(String(50), default='管理员')


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

                    # 与生成表结构无关，仅用于查询方便
                    hobby = relationship("UserType", backref='pers')
                    
            数据添加：
                    session.add(UserType(caption='超级管理员'))
                    session.commit()
                    
                    session.add(Person(name='翔龙',hobby_id=1))
                    session.commit()
        
            user表添加数据，同时也给UserType表添加数据
                    session.add(Person(name='小韩',hobby=UserType(cation='VVIP')))
                    session.commit()
                
            数据查询：
                    正向操作：
                        obj = session.query(Person).filter(Person.nid==2).first()
                        obj.hobby.caption
                    反向操作：
                        obj = session.query(UserType).filter(UserType.id==1).first()
                        obj.pers
            多对多：
                class User2Hobby(Base):
                    __tablename__ = 'user2hobby'
                    id = Column(Integer, primary_key=True, autoincrement=True)
                    hobby_id = Column(Integer, ForeignKey('hobby.id'))
                    user_id = Column(Integer, ForeignKey('user.id'))


                class Hobby(Base):
                    __tablename__ = 'hobby'
                    id = Column(Integer, primary_key=True)
                    title = Column(String(64), unique=True, nullable=False)

                    # 与生成表结构无关，仅用于查询方便
                    users = relationship('User', secondary='user2hobby', backref='hbs')


                class User(Base):
                    __tablename__ = 'user'

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

                    
                添加数据：
                    添加单条：
                        session.add(Hobby(title='篮球'))
                        session.commit()
                    
                        session.add(User(name='梅凯'))
                        session.commit()
                    
                        session.add(User2Hobby(hobby_id=1,user_id=1))
                        session.commit()
                        
                    添加多条
                        正向：
                        obj = Hobby(title='篮球')
                        obj.servers = [User(name='王岩'),User(name='晓梅')]
                        session.add(obj)
                        session.commit()
                    
                        反向：
                        obj = User(title='俊杰')
                        obj.hbs = [Hobby(title='翔龙'),Hobby(title='兴隆')]
                        session.add(obj)
                        session.commit()
                查询：
                    反向：
                    obj = session.query(User).filter(User.id==2).first()
                    obj.hbs
                    
                    正向:
                    obj = session.query(Hobby).filter(Hobby.id==2).first()
                    obj.users

创建session的两种方式

#!/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()

#!/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()

flask-session默认也是使用的第二种方式：scoped_session

- SQL 
            
            a. 
                select * from A where id in (select id from B)  #不能使用*必须与id类型匹配
            b.  #1表示常量，每条数据都添加1
                select 
                    id,
                    name,
                    1
                from A
                
                
                select 
                    id,
                    name,
                    1,
                    (select max(id) from B) as b
                from A
                
                
                
                select 
                    id,
                    name,
                    1,
                    (select max(id) from B where B.xid=A.id) as b
                from A
                
                    +----+---------------+
                    | id | name          |
                    +----+---------------+
                    |  1 | 全栈1期099    |
                    |  2 | 全栈2期099    |
                    +----+---------------+
                    
                    +----+---------+
                    | id | caption |   xid
                    +----+---------+
                    |  1 | 篮球    |    1
                    |  2 | 球      |    1
                    +----+---------+
                
                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`
                """

                
                
                # 也可以使用原生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)
                """