Flask使用SQLAlchemy，db.create_all()报错

Flask项目使用SQLAlchemy，db.create_all()报错

代码如下：

app.py

from flask import Flask, render_template
# import SQLALchemy
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
with app.app_context():
    # set the SQLALCHEMY_DATABASE_URI key
    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///song_library.db'
    app.config['SECRET_KEY'] = 'you-will-never-guess'
    # create an SQLAlchemy object named `db` and bind it to your app
    db = SQLAlchemy(app)

# a simple initial greeting
@app.route('/')
@app.route('/index')
def greeting():
    return render_template('greeting.html')


# app name
@app.errorhandler(404)
def not_found(e):
    return render_template("404.html")

models.py:

from app import app, db


# the User model: each user has a username, and a playlist_id foreign key referring
# to the user's Playlist
class User(db.Model):
    __table_args__ = {'extend_existing': True}
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(50), index=True, unique=True)
    playlist_id = db.Column(db.Integer, db.ForeignKey('playlist.id'))

    # representation method
    def __repr__(self):
        return "{}".format(self.username)

接下来我cd进项目文件夹，输入python3，再执行下面三条命令时

>>> from app import db
>>>> from models import *
>>>> db.create_all()

前两条都能正常执行，最后一条命令会报如下错误：

>>> db.create_all()
Traceback (most recent call last):
  File "", line 1, in 
  File "/Users/luca/opt/anaconda3/lib/python3.9/site-packages/flask_sqlalchemy/extension.py", line 868, in create_all
    self._call_for_binds(bind_key, "create_all")
  File "/Users/luca/opt/anaconda3/lib/python3.9/site-packages/flask_sqlalchemy/extension.py", line 839, in _call_for_binds
    engine = self.engines[key]
  File "/Users/luca/opt/anaconda3/lib/python3.9/site-packages/flask_sqlalchemy/extension.py", line 628, in engines
    app = current_app._get_current_object()  # type: ignore[attr-defined]
  File "/Users/luca/opt/anaconda3/lib/python3.9/site-packages/werkzeug/local.py", line 513, in _get_current_object
    raise RuntimeError(unbound_message) from None
RuntimeError: Working outside of application context.

This typically means that you attempted to use functionality that needed
the current application. To solve this, set up an application context
with app.app_context(). See the documentation for more information.

解决方法1：

cd进项目文件夹之后不要输入python3，而是输入flask shell，再执行上面的三条命令

解法方法2：

cd进项目文件夹之后不要输入python3，而是输入python3.9，再执行上面的三条命令