There's more...

Sometimes, you may want a single SQLAlchemy db instance to be used across multiple applications, or create an application dynamically. In such cases, we might not prefer to bind our db instance to a single application. Here, we will have to work with the application context to achieve the desired outcome.

In this case, we will register our application with SQLAlchemy differently as follows:

from flask import Flask 
from flask_sqlalchemy import SQLAlchemy 
 
db = SQLAlchemy() 
 
def create_app(): 
    app = Flask(__name__) 
    db.init_app(app) 
    return app 

Now, all the operations that were earlier possible globally with the db instance will now require a Flask application context at all times.

The Flask application context is as follows:

>>> from my_app import create_app 
>>> app = create_app() 
>>> app.test_request_context().push() 
>>> # Do whatever needs to be done 
>>> app.test_request_context().pop() 

Or, we can use context manager, shown as follows:

with app(): 
    # We have flask application context now till we are inside the with block