sortBy method
Implementation
RT sortBy(FieldName fieldName, [SortOrder order = SortOrder.asc]) {
validateFieldName(fieldName);
assert(!_query.sortOrder.any((so) => so.fieldName == fieldName),
'$fieldName is already used in the sort order');
_query = _query.copyWith(sortOrder: [
..._query.sortOrder,
FieldSort(fieldName: fieldName, asc: order == SortOrder.asc)
]);
return this as RT;
}