'Converts a known view into a list of keys.
:raises ModelSerializingError: if the view is not listed in `self.views`.'

def _view_to_keys(self, view=None):

    if (view is None):
        view = self.default_view
    if (view not in self.views):
        raise ModelSerializingError('unknown    view', view=view, available_views=self.views)
    return self.views[view][:]
