Python Flask-SQLAlchemy创建数据库报错

Question

使用Flask-SQLAlchemy创建数据库时候报错

此电脑上有MySQL8.0,用户名root,密码eastchinasea,有数据库flask_demo.db

代码:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
import pymysql

app = Flask(__name__)
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True
app.config['SQLALCHEMY_DATABASE_URI'] = (
    'mysql+pymysql://root:eastchinasea@localhost/flask_demo'
)
db = SQLAlchemy(app)


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

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


if __name__ == '__main__':
    db.create_all()

运行结果及详细报错内容:

Traceback (most recent call last):
  File "D:\Program\Python\Python Web\Flask_\SQLflask\manage.py", line 23, in <module>
    db.create_all()
  File "D:\Program\Python\venv\Lib\site-packages\flask_sqlalchemy\extension.py", line 884, in create_all
    self._call_for_binds(bind_key, "create_all")
  File "D:\Program\Python\venv\Lib\site-packages\flask_sqlalchemy\extension.py", line 855, in _call_for_binds
    engine = self.engines[key]
             ^^^^^^^^^^^^
  File "D:\Program\Python\venv\Lib\site-packages\flask_sqlalchemy\extension.py", line 636, in engines
    app = current_app._get_current_object()  # type: ignore[attr-defined]
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Program\Python\venv\Lib\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.

我尝试过的方法:

我把这个

app.config['SQLALCHEMY_DATABASE_URI'] = (
    'mysql+pymysql://root:eastchinasea@localhost/flask_demo'
)

里面的

mysql+pymysql://root:eastchinasea@localhost/flask_demo

修改了很多次,还是有错误,如:

mysql+pymysql://root:eastchinasea@127.0.0.1/flask_demo

mysql+pymysql://root:eastchinasea@localhost/flask_demo.db

改了很多次还是有错误.

我想使用此扩展成功创建数据库

Answer 1

参考GPT和自己的思路：

根据错误信息显示，问题出在当前代码运行的环境上下文中没有应用程序上下文。建议您将 db.create_all() 这个代码包装在 app.app_context() 上下文管理器中。具体修改方法如下：

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
import pymysql

app = Flask(__name__)
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True
app.config['SQLALCHEMY_DATABASE_URI'] = (
    'mysql+pymysql://root:eastchinasea@localhost/flask_demo'
)
db = SQLAlchemy(app)


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

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


if __name__ == '__main__':
    with app.app_context():
        db.create_all()

另外，在配置 app.config['SQLALCHEMY_DATABASE_URI'] 时也可能出现拼写错误或者语法错误，建议仔细检查配置信息是否正确。

如果您还有其他问题或者疑问，可以随时联系我。