Returns a representer for the content type specified in the request.

        :raises HTTPUnsupportedMediaType: If the specified content type is
          not supported.

def _get_request_representer(self):
        """
        Returns a representer for the content type specified in the request.

        :raises HTTPUnsupportedMediaType: If the specified content type is
          not supported.
        """
        try:
            mime_type = \
              get_registered_mime_type_for_string(self.request.content_type)
        except KeyError:
            # The client sent a content type we do not support (415).
            raise HTTPUnsupportedMediaType()
        return as_representer(self.context, mime_type)