flask 操作数据时，db的要在app.config设置之后声明：如app.config['SQLALCHEMY_DATABASE_URI']

#encoding=utf-8

#from foo_orm import Model, Column, String

from flask import Flask, render_template, flash, url_for, redirect
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate

app = Flask(__name__)



import os
app.secret_key = os.getenv(‘SECRET_KEY‘,‘secret string‘)

import os

app.config[‘SQLALCHEMY_DATABASE_URI‘] = os.getenv(‘DATABASE_URL‘,‘sqlite:///‘ + os.path.join(app.root_path, ‘data.db‘))
app.config[‘SQLALCHEMY_TRACK_MODIFICATIONS‘] = False

db = SQLAlchemy(app)
migrate = Migrate(app, db)  # 在db对象创建后调用