FinancialAidSkipView needs a serializer

[singingwolfboy]

Sentry: https://sentry.io/mit-office-of-digital-learning/micromasters/issues/208583737/

Visiting https://micromasters.mit.edu/api/v0/financial_aid_skip/1/ while logged in triggers a 500 exception on production. Reproducing this locally produces an AssertionError with the following error message:

'FinancialAidSkipView' should either include a serializer_class attribute, or override the get_serializer_class() method.

Traceback:

File "/usr/local/lib/python3.5/site-packages/django/core/handlers/exception.py" in inner
  39.             response = get_response(request)

File "/usr/local/lib/python3.5/site-packages/django/core/handlers/base.py" in _legacy_get_response
  249.             response = self._get_response(request)

File "/usr/local/lib/python3.5/site-packages/django/core/handlers/base.py" in _get_response
  217.                 response = self.process_exception_by_middleware(e, request)

File "/usr/local/lib/python3.5/site-packages/django/core/handlers/base.py" in _get_response
  215.                 response = response.render()

File "/usr/local/lib/python3.5/site-packages/django/template/response.py" in render
  109.             self.content = self.rendered_content

File "/usr/local/lib/python3.5/site-packages/rest_framework/response.py" in rendered_content
  72.         ret = renderer.render(self.data, accepted_media_type, context)

File "/usr/local/lib/python3.5/site-packages/rest_framework/renderers.py" in render
  701.         context = self.get_context(data, accepted_media_type, renderer_context)

File "/usr/local/lib/python3.5/site-packages/rest_framework/renderers.py" in get_context
  635.         raw_data_put_form = self.get_raw_data_form(data, view, 'PUT', request)

File "/usr/local/lib/python3.5/site-packages/rest_framework/renderers.py" in get_raw_data_form
  548.                     serializer = view.get_serializer(instance=instance)

File "/usr/local/lib/python3.5/site-packages/rest_framework/generics.py" in get_serializer
  109.         serializer_class = self.get_serializer_class()

File "/usr/local/lib/python3.5/site-packages/rest_framework/generics.py" in get_serializer_class
  126.             % self.__class__.__name__

Exception Type: AssertionError at /api/v0/financial_aid_skip/1/
Exception Value: 'FinancialAidSkipView' should either include a `serializer_class` attribute, or override the `get_serializer_class()` method.

[singingwolfboy]

https://sentry.io/mit-office-of-digital-learning/micromasters/issues/208583737/

[pdpinch]

Is this a user-facing error? Do you know if this is a regression?

[singingwolfboy]

It's user-facing in the sense that a user could discover it, but I don't think it's preventing users from doing anything on the production site. I discovered this bug while trying to manually test a pull request related to coupons, but I suspect that I uncovered it because the course price was negative.

[singingwolfboy]

However, I should add that this is a totally silent failure in the UI. Workflow:

• On the dashboard page, I click on the "Skip this and Pay Full Price" button.
• A confirmation dialog appears. I click on "Pay Full Price".
• The dialog disappears. The browser makes a PATCH request to the API, which is not visible in the UI.
• The request fails with a 500 exception. No error message is shown to the user. It seems like clicking "Skip this and Pay Full Price" did nothing at all.

At the very least, we should display an error message to the user, in the event that something goes wrong like this.

[pdpinch]

So the only time we've seen this happen is when the course price is negative?

But if we wrote a proper serializer we could return an error message to the user in the case of any 500 error from this API?

[singingwolfboy]

So the only time we've seen this happen is when the course price is negative?

Correct. However, I don't know that it couldn't happen with a positive course price.

But if we wrote a proper serializer we could return an error message to the user in the case of any 500 error from this API?

A proper serializer could return an error message, but it wouldn't be displayed to the user unless the Javascript was set up to do so. I just made #2430 to display an error message, independent of the serializer in the backend.