如何在Django的MultiValueDictKeyError上以400响应？

Question

Coming from Flask, request.args[key] and request.form[key] responds with 400 if the key doesn't exist. This has a nice property of failing fast .

In Django, request.GET[key] and request.FORM[key] raises HttpResponseBadRequest if the key doesn't exist, which causes your API to respond with a 500 status if unhandled. I've seen other answers recommending request.GET.get(key) , but that inadvertently loosens the API contract that could allow client-side bugs to slip by (eg a query parameter typo, forgetting to include a param, etc).

I could manually check for required query params:

arg1 = request.POST.get('arg1')
if not arg1:
    raise HttpBadRequest('"arg1" was not provided.')

arg2 = request.POST.get('arg2')
if not arg2:
    raise HttpBadRequest('"arg1" was not provided.')

arg3 = request.POST.get('arg3')
if not arg3:
    raise HttpBadRequest('"arg3" was not provided.')

But that leaves a lot of room for error. (Did you notice the typo?)

I could manually handle HttpResponseBadRequest :

def my_view(request):
    try:
        arg1 = request.POST['arg1']
        arg2 = request.POST['arg2']
        arg3 = request.POST['arg3']
    except MultiValueDictKeyError as ex:
        raise HttpBadRequest('"{}" was not provided.'.format(ex))

But now you have an extra thing to remember when writing views.

Compare the above examples to Flask's equivalent:

arg1 = request.form['arg1']
arg2 = request.form['arg2']
arg3 = request.form['arg3']

How can I write the same thing in Django without extra boilerplate in my views and have it respond with 400 when a param is missing?

Answer 1

This is exactly you should use Django forms . They are the validation framework that checks the user input and returns errors when it is not valid.

(Note, it's not the accessing of the nonexistent key that raises BadRequest; it raises MultiValueDictKeyError, as one of your snippet notes, and if that is unhandled the response middleware will return BadRequest.)