Flask和SQLAlchemy -如何从配置文件中获取连接字符串？

# 配置文件示例

# 开发环境配置
class DevelopmentConfig:
    DATABASE = {
        'driver': 'mysql',
        'host': 'localhost',
        'port': '3306',
        'database': 'mydatabase',
        'username': 'myusername',
        'password': 'mypassword'
    }

# 测试环境配置
class TestingConfig:
    DATABASE = {
        'driver': 'postgresql',
        'host': 'localhost',
        'port': '5432',
        'database': 'mydatabase',
        'username': 'myusername',
        'password': 'mypassword'
    }

# 生产环境配置
class ProductionConfig:
    DATABASE = {
        'driver': 'mongodb',
        'host': 'localhost',
        'port': '27017',
        'database': 'mydatabase',
        'username': 'myusername',
        'password': 'mypassword'
    }

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)

# 加载配置文件
app.config.from_object('config.DevelopmentConfig')

# 初始化SQLAlchemy
db = SQLAlchemy(app)

# 使用连接字符串配置SQLAlchemy
app.config['SQLALCHEMY_DATABASE_URI'] = '{driver}://{username}:{password}@{host}:{port}/{database}'.format(
    driver=app.config['DATABASE']['driver'],
    username=app.config['DATABASE']['username'],
    password=app.config['DATABASE']['password'],
    host=app.config['DATABASE']['host'],
    port=app.config['DATABASE']['port'],
    database=app.config['DATABASE']['database']
)

# 其他应用代码...