return _lodash2['default'].chain(sortBy).filter(function (key) {
    var hasSortDir = key[0] === ' ' || key[0] === '+' || key[0] === '-';
    var isValidField = _lodash2['default'].contains(validFields, key.substring(1));
    return hasSortDir && isValidField;
  }).reduce(function (result, key) {