Flask-SQLAlchemy

'数据库类型+数据库驱动名称://用户名:口令@机器地址:端口号/数据库名'

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,  # 池中没有线程时，最多等待的时间，超时报错，默认30秒
    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），-1代表永远不回收，即一直被重用
)
 
 
def task(arg):
    conn = engine.raw_connection()　　#拿到的是一个原生的pymysql连接对象
    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()

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()   # 创建对象的基类:

# 定义User对象:
class Users(Base):
    # 表的名字:
    __tablename__ = 'users'

    # 表的结构:
    id = Column(Integer, primary_key=True)
    name = Column(String(32), index=True, nullable=False,default='xx')   # index指定是否是索引，nullable是否能为空
    email = Column(String(32), unique=True)   # 指定唯一
    ctime = Column(DateTime, default=datetime.datetime.now) #注意，此处设置时datetime.datetime.now若加了括号，则时间永远是程序启动时的时间，后面创建数据时，不会变化
    extra = Column(Text, nullable=True)

    __table_args__ = (
        UniqueConstraint('id', 'name', name='uix_id_name'), # 联合唯一索引
        Index('ix_id_name', 'name', 'email'), #给name和email创建普通索引，索引名为ix_id_name
    )


def init_db():
    """
    根据类创建数据库表
    :return: 
    """
    # 初始化数据库连接:
    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) #找到所有继承了Base的类，按照其结构建表


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()

    __table_args__ = {
        'mysql_engine': 'InnoDB',   # 指定表的引擎
        'mysql_charset': 'utf8'     # 指定表的编码格式
    }

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()   # 创建对象的基类:


# ##################### 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"))  #建FK关系

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


# ##################### 多对多示例 #########################
# 这里多对多需要自己建第三张表，并绑定关系
class Server2Group(Base):   
    __tablename__ = 'server2group'
    id = Column(Integer, primary_key=True, autoincrement=True)  #autoincrement 设置自增
    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')    #反向关联的名字


class Server(Base):
    __tablename__ = 'server'

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


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/userinfo?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/userinfo?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 -*-
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)    #创建Session类
  
# 每次执行数据库操作时，都需要创建一个session
session = Session()    # 创建session对象:
  
# ############# 执行ORM操作 #############
# 创建新User对象
obj1 = Users(name="alex1")    
# 添加到session:
session.add(obj1)
# 提交即保存到数据库:
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 sqlalchemy.sql import text
from sqlalchemy.engine.result import ResultProxy
from db import Users, Hosts

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

session = Session()

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

# 添加
cursor = session.execute('insert into users(name) values(:value)',params={"value":'hc'})
# 注意占位符和传参的形式
session.commit()
print(cursor.lastrowid)

session.close()

原生SQL语句

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/s6", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)

session = Session()

# ################ 添加 ################

obj1 = Users(name="hc")
session.add(obj1)   #添加一个对象

session.add_all([
    Users(name="hc"),
    Users(name="alex"),
    Hosts(name="c1.com"),
])      #添加多个对象
session.commit()


# ################ 删除 ################

# filter是where条件，最后调用one()或first()返回唯一行，如果调用all()则返回所有行
session.query(Users).filter(Users.id > 2).delete()  #删除Users表中id大于2的数据
session.commit()

# ################ 修改 ################

session.query(Users).filter(Users.id > 0).update({"name" : "099"})  # 将Users表中id>0的数据，把name字段改为099
session.query(Users).filter(Users.id > 0).update({Users.name: Users.name + "099"}, synchronize_session=False)  #synchronize_session设置为False即执行字符串拼接
session.query(Users).filter(Users.id > 0).update({"age": Users.age + 1}, synchronize_session="evaluate")    #synchronize_session设置为evaluate即执行四则运算
session.commit()

# ################ 查询 ################

r1 = session.query(Users).all()
r2 = session.query(Users.name.label('xx'), Users.age).all()     #label 取别名的，即在查询结果中，显示name的别名'xx'
r3 = session.query(Users).filter(Users.name == "alex").one()    # one()返回唯一行,类似于django的get,如果返回数据为多个则报错
r3 = session.query(Users).filter(Users.name == "alex").all()    # all()获取所有数据
r4 = session.query(Users).filter_by(name='alex').all()          # 注意filter和filter_by后面括号内条件的写法
r5 = session.query(Users).filter_by(name='alex').first()        # first()获取返回数据的第一行
r6 = session.query(Users).filter(text("id<:value and name=:name")).params(value=224, name='fred').order_by(Users.id).all()  
#order_by后面还可以.desc()降序排列，默认为.asc()升序排列
# text(自定义条件，:的功能类似%s占位)，params中进行传参
r7 = session.query(Users).from_statement(text("SELECT * FROM Hosts where name=:name")).params(name='ed').all()
# text中还能从另一个表中查询，前面要用from_statement，而不是filter


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 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()
# 添加
"""
session.add_all([
    Hobby(caption='乒乓球'),
    Hobby(caption='羽毛球'),
    Person(name='张三', hobby_id=3),
    Person(name='李四', hobby_id=4),
])

person = Person(name='张九', hobby=Hobby(caption='姑娘'))
session.add(person)

hb = Hobby(caption='人妖')
hb.pers = [Person(name='文飞'), Person(name='博雅')]
session.add(hb)     #  会同时创建3条数据(1条hobby的数据，2条person的数据)

session.commit()
"""

# 使用relationship正向查询
"""
v = session.query(Person).first()
print(v.name)
print(v.hobby.caption)
"""

# 使用relationship反向查询
"""
v = session.query(Hobby).first()
print(v.caption)
print(v.pers)
"""

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 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()
# 添加
"""
session.add_all([
    Server(hostname='c1.com'),
    Server(hostname='c2.com'),
    Group(name='A组'),
    Group(name='B组'),
])
session.commit()

s2g = Server2Group(server_id=1, group_id=1)
session.add(s2g)
session.commit()


gp = Group(name='C组')
gp.servers = [Server(hostname='c3.com'),Server(hostname='c4.com')]
session.add(gp)
session.commit()


ser = Server(hostname='c6.com')
ser.groups = [Group(name='F组'),Group(name='G组')]
session.add(ser)
session.commit()
"""


# 使用relationship正向查询
"""
v = session.query(Group).first()
print(v.name)
print(v.servers)
"""

# 使用relationship反向查询
"""
v = session.query(Server).first()
print(v.hostname)
print(v.groups)
"""


session.close()

基于relationship操作m2m

#　条件
ret = session.query(Users).filter_by(name='alex').all()
ret = session.query(Users).filter(Users.id > 1, Users.name == 'eric').all()
ret = session.query(Users).filter(Users.id.between(1, 3), Users.name == 'eric').all()
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()

from sqlalchemy import and_, or_    #需要导入

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
ret = session.query(Users)[1:2]

# 排序
ret = session.query(Users).order_by(Users.name.desc()).all()  # 倒序排列
ret = session.query(Users).order_by(Users.name.desc(), Users.id.asc()).all()    

# 分组
from sqlalchemy.sql import func   #需要导入

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
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()

#!/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/s6?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()

        子查询：
            session.query(Users).filter(Users.id.in_(session.query(Users.id).filter_by(name='eric'))).all()
            """
            select * from users where id in (select id from xxx)
            """
        
        
            subqry = session.query(func.count(Server.id).label("sid")).filter(Server.id == Group.id).correlate(Group).as_scalar()
            #第一步：  session.query(func.count(Server.id).label("sid")).filter(Server.id == Group.id)
            #这句的sql语句为 select count(id) as sid from server where server.id = group.id      如果直接运行，则会报错
            # 第二步：.correlate(Group).as_scalar() ==> 代表此时不执行查询操作，将其当作条件，在group表中查询时，才执行查询
            
                    
            result = session.query(Group.name, subqry)
            # sql语句为：select group.name  subqry  from group
            #第三步：将subqry替换为上面的条件，则此句的SQL为：
            #    select group.name,(select count(id) as sid from server where server.id = group.id) as xx  from group

from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine

engine = create_engine(
    "mysql+pymysql://root:123@47.93.4.198:3306/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）
)
Session = sessionmaker(bind=engine)

# 方式一：
# 由于无法提供线程共享功能，所有在开发时要注意，在每个线程中自己创建 session。
#  from sqlalchemy.orm.session import Session
#         具有操作数据库的：'close', 'commit', 'connection', 'delete', 'execute', 'expire',.....
session = Session()     # 创建普通的session
print('原生session',session)
# 操作数据库
session.close()

由于无法提供线程共享功能，所有在开发时要注意，在每个线程中自己创建 session解决办法如下：

#!/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()

from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session

engine = create_engine(
    "mysql+pymysql://root:123@47.93.4.198:3306/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）
)
Session = sessionmaker(bind=engine)

# 方式二：支持线程安全，自动为每个线程创建一个session，单线程时，只创建一个
#               - threading.Local
#               - 唯一标识
# ScopedSession对象
#       self.registry(), 加括号 创建session
#       self.registry(), 加括号 创建session
#       self.registry(), 加括号 创建session
from greenlet import getcurrent as get_ident #本地线程的唯一标识的函数，加括号则执行函数
session = scoped_session(Session,get_ident)
# session.add
# 操作数据库
session.remove()

支持线程安全，自动为每个线程创建一个session，单线程时，只创建一个

pip install sqlalchemy-utils

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column,Integer,String
from sqlalchemy_utils import ChoiceType
from sqlalchemy import create_engine

Base = declarative_base()
class User(Base):
    __tablename__ = 'users'
    type_choices=(
        (1,'北京'),
        (2,'上海'),
        )
    id = Column(Integer, primary_key=True)  #必须要有主键
    name =Column(String(64))
    types=Column(ChoiceType(type_choices,Integer()))    # 注意：Integer后面要有括号

    __table_args__ = {
        'mysql_engine': 'InnoDB',
        'mysql_charset': 'utf8'
    }

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/db1?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/db1?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 -*-
# __author__ = "HuChong"
# Date: 2018/1/12

from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from ru import User

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/db1", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)

session = Session()

obj1 = User(name="xz",types=1)
obj2 = User(name="zz",types=2)
session.add_all([obj1,obj2])
session.commit()
session.close()

#! /usr/bin/env python
# -*- coding: utf-8 -*-
# __author__ = "HuChong"
# Date: 2018/1/12

from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from ru import User

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/db1", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)

session = Session()

result_list=session.query(User).all()
print(result_list)
for item in result_list:
    print(item.types)
    print(item.types.code,item.types.value)

session.close()


#######打印结果如下########
'''
[<ru.User object at 0x0386D770>, <ru.User object at 0x0386D7D0>]
Choice(code=1, value=北京)
1 北京
Choice(code=2, value=上海)
2 上海
'''

pip install flask-sqlalchemy

# 1. 引入Flask-SQLAlchemy
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()    #实例化SQLAlchemy对象

# 2. 注册 Flask-SQLAlchemy
    # SQLAlchemy(app)
    # 由于这个对象在其他地方想要使用，所有用以下方式注册 
    db.init_app(app) #读取配置文件，配置文件中写以前在create_engine里面的链接数据

#settings.py中，加上配置

# 3. 导入models中的表
from .models import *

from sqlalchemy import Column, Integer, String, Text, ForeignKey, DateTime, UniqueConstraint, Index
from app import db

# 4. 写类继承db.Model
class Users(db.Model):  #再不是继承Base，而且继承db.Model
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    name = Column(String(32), index=True, nullable=False)
    pwd = Column(String(32))

    __table_args__ = {
        'mysql_engine': 'InnoDB',   # 指定表的引擎
        'mysql_charset': 'utf8'     # 指定表的编码格式
    }


class Group(db.Model):
    __tablename__ = 'group'

    id = Column(Integer, primary_key=True)
    name = Column(String(32), index=True, nullable=False)

    __table_args__ = {
        'mysql_engine': 'InnoDB',
        'mysql_charset': 'utf8'
    }

# 5. 创建和删除表
  #  以后执行db.create_all()
  #  以后执行db.drop_all()
但是这样不好，我们引入 Flask-Migrate

安装  pip install Flask-Migrate

# 5.1 导入
from flask_migrate import Migrate, MigrateCommand
from app import create_app, db

app = create_app()
manager = Manager(app)
# 5.2 创建migrate实例
migrate = Migrate(app, db)

#执行命令：
    初次：python manage.py db init
    
    python manage.py db migrate
    python manage.py db upgrade

以后执行SQL时：
    方式一：
        result = db.session.query(models.User.id,models.User.name).all()
        db.session.remove()
    方式二：
        result = models.Users.query.all()

pip  freeze  # 获取环境中所有安装的模块以及其对应的版本
        
pip  freeze > requirements.txt  # 生成对应的文本文件

 pip install pipreqs

# 获取当前所在程序目录中涉及到的所有模块，并自动生成 requirements.txt 且写入内容。
 pipreqs ./

安装requirements.txt依赖
pip install -r requirements.txt