python - 尝试在 Flask View 中实例化 WTForms 对象时出现 "Runtime Error: working outside of application context"

Question

所以我有一个这样定义的表单:

class NewDashForm(Form):
    tabname = StringField('tabname', validators=[DataRequired(),Length(1,16)])
    title = StringField('title', validators=[DataRequired(),Length(1,128)])

我将它导入到我的views.py 文件中，但是当我尝试像这样实例化它时:

form = NewDashForm()

我收到“在应用程序上下文之外工作”错误。该应用程序是通过“工厂”方法生成的，如下所示:

def generate_application(config=None):
   application = Flask(__name__)
   application.config.from_object(config)
   application.register_blueprint(cheda.generate_blueprint(application.config,application.db))
   return application

我在最后一个代码片段中遗漏了一些与数据库相关的内容，但您明白了。根据我的理解， View 中发生的任何事情都应该自动在应用程序上下文中，但显然我遗漏了一些东西。我在这里做错了什么？

Traceback (most recent call last):
  File "/vagrant/venv/cheda_env/bin/cheda-run", line 9, in <module>
    load_entry_point('cheda==0.1.0', 'console_scripts', 'cheda-run')()
  File "/vagrant/venv/cheda_env/lib/python3.4/site-packages/pkg_resources/__init__.py", line 546, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/vagrant/venv/cheda_env/lib/python3.4/site-packages/pkg_resources/__init__.py", line 2666, in load_entry_point
    return ep.load()
  File "/vagrant/venv/cheda_env/lib/python3.4/site-packages/pkg_resources/__init__.py", line 2339, in load
    return self.resolve()
  File "/vagrant/venv/cheda_env/lib/python3.4/site-packages/pkg_resources/__init__.py", line 2345, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/code/cheda/cheda/cmd/run.py", line 10, in <module>
    from .. import application
  File "/code/cheda/cheda/application.py", line 16, in <module>
    from .blueprints import cheda
  File "/code/cheda/cheda/blueprints/cheda.py", line 10, in <module>
    from ..views import views as cheda_views
  File "/code/cheda/cheda/views/views.py", line 37, in <module>
    class NewDash(JsonApiView):
  File "/code/cheda/cheda/views/views.py", line 39, in NewDash
    form = NewDashForm()
  File "/vagrant/venv/cheda_env/lib/python3.4/site-packages/wtforms/form.py", line 212, in __call__
    return type.__call__(cls, *args, **kwargs)
  File "/vagrant/venv/cheda_env/lib/python3.4/site-packages/flask_wtf/form.py", line 68, in __init__
    csrf_enabled = current_app.config.get('WTF_CSRF_ENABLED', True)
  File "/vagrant/venv/cheda_env/lib/python3.4/site-packages/werkzeug/local.py", line 338, in __getattr__
    return getattr(self._get_current_object(), name)
  File "/vagrant/venv/cheda_env/lib/python3.4/site-packages/werkzeug/local.py", line 297, in _get_current_object
    return self.__local()
  File "/vagrant/venv/cheda_env/lib/python3.4/site-packages/flask/globals.py", line 34, in _find_app
    raise RuntimeError('working outside of application context')
RuntimeError: working outside of application context

Answer 1

您应该只在 View 函数中实例化表单，在请求之外这样做是没有意义的。您收到错误是因为它试图从请求中获取数据，但该数据不存在。

如果您确实需要事先实例化它，可以将空数据传递给它，这样它就不会查看请求，或者使用请求上下文。

from werkzeug.datastructrues import MultiDict
form = MyForm(MultiDict())

# or

with app.test_request_context():
    form = MyForm()

同样，您永远不应该在应用程序中执行此操作，表单仅在请求期间在 View 内有用。如果您想在单元测试中测试表单，测试请求上下文将会很有用。