AttributeError: 'NoneType' 对象没有属性 'drivername'

Question

当我启动我的应用程序时出现此错误。显然它与 SQLAlchemy 有一些关系。我一直在 Corey Schaffer Flask 教程的帮助下处理这个例子。

> File "C:\Users\Matea\venv\lib\site-packages\flask\app.py", line 2309, in __call__
return self.wsgi_app(environ, start_response)
File "C:\Users\Matea\venv\lib\site-packages\flask\app.py", line 2295, in wsgi_app
response = self.handle_exception(e)
File "C:\Users\Matea\venv\lib\site-packages\flask\app.py", line 1741, in handle_exception
reraise(exc_type, exc_value, tb)
File "C:\Users\Matea\venv\lib\site-packages\flask\_compat.py", line 35, in reraise
raise value
File "C:\Users\Matea\venv\lib\site-packages\flask\app.py", line 2292, in wsgi_app
response = self.full_dispatch_request()
File "C:\Users\Matea\venv\lib\site-packages\flask\app.py", line 1815, in full_dispatch_request
rv = self.handle_user_exception(e)
File "C:\Users\Matea\venv\lib\site-packages\flask\app.py", line 1718, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "C:\Users\Matea\venv\lib\site-packages\flask\_compat.py", line 35, in reraise
raise value
File "C:\Users\Matea\venv\lib\site-packages\flask\app.py", line 1813, in full_dispatch_request
rv = self.dispatch_request()
File "C:\Users\Matea\venv\lib\site-packages\flask\app.py", line 1799, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "C:\Users\Matea\myblog\myblog\main\routes.py", line 11, in home
posts = Post.query.order_by(Post.date_posted.desc()).paginate(page=page, per_page=5)
File "C:\Users\Matea\venv\lib\site-packages\flask_sqlalchemy\__init__.py", line 514, in __get__
return type.query_class(mapper, session=self.sa.session())
File "C:\Users\Matea\venv\lib\site-packages\sqlalchemy\orm\scoping.py", line 74, in __call__
return self.registry()
File "C:\Users\Matea\venv\lib\site-packages\sqlalchemy\util\_collections.py", line 1001, in __call__
return self.registry.setdefault(key, self.createfunc())
File "C:\Users\Matea\venv\lib\site-packages\sqlalchemy\orm\session.py", line 2950, in __call__
return self.class_(**local_kw)
File "C:\Users\Matea\venv\lib\site-packages\flask_sqlalchemy\__init__.py", line 143, in __init__
bind = options.pop('bind', None) or db.engine
File "C:\Users\Matea\venv\lib\site-packages\flask_sqlalchemy\__init__.py", line 877, in engine
return self.get_engine()
File "C:\Users\Matea\venv\lib\site-packages\flask_sqlalchemy\__init__.py", line 896, in get_engine
return connector.get_engine()
File "C:\Users\Matea\venv\lib\site-packages\flask_sqlalchemy\__init__.py", line 556, in get_engine
self._sa.apply_driver_hacks(self._app, info, options)
File "C:\Users\Matea\venv\lib\site-packages\flask_sqlalchemy\__init__.py", line 830, in apply_driver_hacks
if info.drivername.startswith('mysql'):
AttributeError: 'NoneType' object has no attribute 'drivername'

这是一些代码：这是来自我的init .py

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from flask_bcrypt import Bcrypt
from flask_login import LoginManager
from flask_mail import Mail
from myblog.config import Config


db = SQLAlchemy()
bcrypt = Bcrypt()
login_manager = LoginManager()
login_manager.login_view = 'users.login'
login_manager.login_message_category = 'info'
mail = Mail()


def create_app(config_class=Config):
    app = Flask(__name__)
    app.config.from_object(Config)

    db.init_app(app)
    bcrypt.init_app(app)
    login_manager.init_app(app)
    mail.init_app(app)

    from myblog.users.routes import users
    from myblog.posts.routes import posts
    from myblog.main.routes import main
    from myblog.errors.handlers import errors
    app.register_blueprint(users)
    app.register_blueprint(posts)
    app.register_blueprint(main)
    app.register_blueprint(errors)

    return app

这段代码来自 config.py

import os


class Config:
    SECRET_KEY = os.environ.get('SECRET_KEY')
    SQLALCHEMY_DATABASE_URI = os.environ.get('SQLALCHEMY_DATABASE_URL')
    MAIL_SERVER = 'smtp.googlemail.com'
    MAIL_PORT = 587
    MAIL_USE_TLS = True
    MAIL_USERNAME = os.environ.get('EMAIL_USER')
    MAIL_PASSWORD = os.environ.get('EMAIL_PASS')

我希望你能帮助我，如果有什么遗漏，请告诉我，谢谢！

Answer 1

如果您已正确设置.bash_proflie中的环境变量

    export EMAIL_USER='youremail@gmail.com'
    export EMAIL_PASS='Yourpassword'
    export SQLALCHEMY_DATABASE_URI='sqlite:///site.db'
    export SECRET_KEY='secretkeyxxxxxxxxxxxxxxxx'

然后尝试重新启动计算机。
如果仍然失败*尝试在python中创建数据库*

from your yourflaskapp import db
db.create_all()

如果您的应用程序位于蓝图中

    use from yourapp import create_app
    app = create_app()
    app.app_context().push()

进行更改后，请务必刷新文本编辑器和终端。另请尝试确保您在正确的目录中运行应用程序。

欲了解更多信息，请访问蓝图使用

http://flask-sqlalchemy.pocoo.org/2.3/contexts/

Answer 2

@Ivan M，我正在学习相同的教程，也遇到了这个问题。发生这种情况是因为讲师将数据库 URI 和其他参数移至环境变量中（请参阅第 11 部分，大约第 27 分钟）。这是一项安全措施和良好的开发实践。
为了使配置文件正常工作，请恢复 init.py 中的更改并更新 config.py 以使用直接链接而不是方括号：
SQLALCHEMY_DATABASE_URI = 'sqlite:///site.db'
UPD：同样适用于SECRET_KEY您希望硬编码的其他参数：
SECRET_KEY = '5791628bb0b13ce0c676dfde280ba245'