'Check that `ordering` refers to existing fields.'

def _check_ordering_item(self, obj, model, field_name, label):

    if ((field_name == '?') and (len(obj.ordering) != 1)):
        return [checks.Error("The    value    of    'ordering'    has    the    random    ordering    marker    '?',    but    contains    other    fields    as    well.", hint='Either    remove    the    "?",    or    remove    the    other    fields.', obj=obj.__class__, id='admin.E032')]
    elif (field_name == '?'):
        return []
    elif (LOOKUP_SEP in field_name):
        return []
    else:
        if field_name.startswith('-'):
            field_name = field_name[1:]
        if (field_name == 'pk'):
            return []
        try:
            model._meta.get_field(field_name)
        except FieldDoesNotExist:
            return refer_to_missing_field(field=field_name, option=label, model=model, obj=obj, id='admin.E033')
        else:
            return []
