I was pulling my hair out yesterday afternoon and this morning trying to figure out how to get Flask RESTPlus to return a different error code for validation errors. Out of the box, it will return a 400 code with the validation error messages (as it should). Unfortunately, I was tasked with writing an endpoint that would fulfill a previously determined contract; this contract expects either a 200 or a 500.

Custom validation

One thought I had was to disable the RESTPlus validation and do my own validation. You can use the validate=False argument in Namespace.expect() to supply an expected request format (for Swagger documentation) while ignoring validation of that model.

    @ns.expect(myRequestModel, validate=False)
    def post(self):
        #Do custom validation and return a 500 if it fails

Unfortunately, this is a lot of wheel reinventing for very little gain.

Overriding RESTPlus validation

After pouring over the documentation and source code, I eventually arrived at the following solution. Of course, there may be better ways to do it, but this was the way I finally got it to work.

class MyResource(Resource):

    # Override validate_payload method from Resource class
    def validate_payload(self, func):
        try:
            super(Resource, self).validate_payload(func)
        except BadRequest as e:
            abort(status.HTTP_500_INTERNAL_SERVER_ERROR, **e.data)

Fortunately, this resource was only used for this single non-conformant contract. Otherwise, I would probably have to split it out to avoid having the custom validation apply to other endpoints.