数据库进去查找desc结构能看到，但select * from user就什么都没有？

Question

from sqlalchemy import create_engineHOSTusername = '127.0.0.1' # ip地址PORT = '3306' # 端口号DATABASE = 'test' # 数据库名USERusername = 'root' # 用户名PASSWORD = 'root' # 用户登录密码DB_URI = 'mysql+pymysql://{}:{}@{}:{}/{}?charset=utf8'.format(USERusername, PASSWORD, HOSTusername, PORT, DATABASE)engine = create_engine(DB_URI)from sqlalchemy.ext.declarative import declarative_baseBase = declarative_base(engine)from sqlalchemy import Column,Integer,Stringclass User(Base):__tableusername__ = 'user'id = Column(Integer,primary_key=True,autoincrement=True)userusername = Column(String(50),nullable=False)password = Column(String(100))def __repr__(self):return '<User(id="%s",userusername="%s",password="%s)>' % (self.id, self.userusername, self.password)Base.metadata.create_all()from sqlalchemy.orm import sessionmakerSession = sessionmaker(engine)session = Sessiondef add_user():qa = User(username='qa', password='123456')qb = User(username='qb', password='888888')session.add(qa)session.add(qb)ls = [User(username='qc', password='888888'),User(username='qd', password='666666')]session.add_all(ls)session.commit()add_user()有缩进，提交问题时显现，运行结果有一句sqlalchemy.exc.InvalidRequestError: Class <class '__main__.User'> does not have a __table__ or __tablename__ specified and does not inherit from an existing table-mapped class.，是没有对应数据库表头嘛？英文不太好，数据库进去查找desc结构能看到，select * from user就什么都没有，不解

Answer 1

python3下用flask-sqlalchemy对mysql数据库操作案例：
from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://username:password@localhost/db_name'
db = SQLAlchemy(app)

class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(80), unique=True)
email = db.Column(db.String(120), unique=True)

def __init__(self, username, email):
self.username = username
self.email = email

def __repr__(self):
return '<User %r>' % self.username

admin = User('admin', '[e-mail]')

db.create_all() # In case user table doesn't exists already. Else remove it.

db.session.add(admin)

db.session.commit() # This is needed to write the changes to database

User.query.all()

User.query.filter_by(username='admin').first()