如何关闭我在线程中使用的Flask-SQLAlchemy连接？

from flask import Flask, g
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'your_database_uri'
db = SQLAlchemy(app)

@app.before_request
def before_request():
    g.db = db.get_engine().connect()

@app.teardown_request
def teardown_request(exception=None):
    db = getattr(g, 'db', None)
    if db is not None:
        db.close()

# 其他路由和视图函数

if __name__ == '__main__':
    app.run()