RuntimeError: The current Flask app is not registered with this 'SQLAlchemy' instance. Did you forget to call 'init_app', or did you create multiple 'SQLAlchemy' instances?

这个错误通常是因为在使用 Flask 和 SQLAlchemy 时没有正确初始化 SQLAlchemy 实例。你应该在创建 SQLAlchemy 实例后，调用 `init_app` 方法将其绑定到 Flask 应用程序上下文中。示例如下：

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
db = SQLAlchemy()

def create_app():
    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///example.db'
    db.init_app(app)

    # ... 其他 Flask 初始化代码 ...

    return app

如果你已经调用了 `init_app` 方法，那么可能是你创建了多个 SQLAlchemy 实例，需要检查并确保只有一个实例与 Flask 应用程序相关联。

相关问题

File E:\python3.7.7\lib\site-packages\flask_sqlalchemy\extension.py, line 308, in init_app Either SQLALCHEMY_DATABASE_URI or SQLALCHEMY_BINDS must be set. RuntimeError: Either SQLALCHEM

Y_DATABASE_URI or SQLALCHEMY_BINDS must be set is a common error in Flask-SQLAlchemy. This error is raised when the Flask application is not configured properly to use SQLAlchemy.

To fix this error, you need to set the SQLALCHEMY_DATABASE_URI configuration variable in your Flask application configuration. This variable should contain the connection string for your database.

Here is an example of how to set the SQLALCHEMY_DATABASE_URI variable:

app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://user:password@localhost/mydatabase'

You can also set the SQLALCHEMY_BINDS variable if you need to connect to multiple databases.

Once you have set the configuration variables, you should be able to initialize the Flask-SQLAlchemy extension without any errors.