Comparators for grid columns sorting

I'm using a backend persistence framework which expose SQL tables as Streams and builds SQL queries with its own implementation of Predicate and Comparator.

I thought this would create a perfect match with FW8 data providers, but I'm facing some difficulties with sorting, since the QuerySortOrder only provides strings to identify the properties, where a stream wants a Comparator.

I know Query has a getInMemorySorting() which return a Comparator, but how to set a particular comparator for a column? There's a setComparator(SerializableComparator comparator), but I cannot pass a custom implementation of Comparator, nor can I use the suggested comparator::compare since that will return a new object and not the backend-optimized implementation.

I'm suggesting here to decouple Query from SortOrder<String> and let the developer decide to use, for example, SortOrder<Comparator<T>>.

Start by reading Query, QuerySortOrder, and SerializableComparator, especially Query.getInMemorySorting() and setComparator(SerializableComparator). Determine how sorting is represented across data providers and what API shape can support backend-specific comparators. Done means a decided, compatible design for column comparators, with affected behavior and tests identified.