def init(req, model):
    rels = model.relationships
    fields = model.all_fields
    params = req.get_param_as_list('sort') or [goldman.config.SORT]
    params = [Sortable(param.lower()) for param in params]
    for param in params:
        _validate_no_rels(param, rels)
        _validate_field(param, fields)
    return params