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?

这个错误是由于Flask app没有正确注册到SQLAlchemy实例所引起的。有两种可能的原因：

1. 您可能没有在Flask app中调用SQLAlchemy的init_app()方法。在您的Flask应用程序中，您需要使用app.config属性来设置SQLAlchemy的配置，然后调用SQLAlchemy的init_app()方法，以便将其与Flask应用程序关联起来。例如：

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///example.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False

db = SQLAlchemy()
db.init_app(app)

2. 另一个可能的原因是您创建了多个SQLAlchemy实例。如果您创建了多个SQLAlchemy实例并尝试在不同的应用程序上下文中使用它们，则可能会出现此错误。请确保在应用程序中只创建一个SQLAlchemy实例，并在需要时将其传递给其他部分。

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.