I can not get custom sorts and Cursor Pagination working

[JanMisker]

I have a custom sort that orders by a relationship value (localized title that is in a Metadata model/table), works fine until I start paginating with cursor pagination.

Originally I was ordering on a select in the orderBy, similar to the example in the spatie docs with StringLengthSort, but that does not work with CursorPaginator because it analyzes the ORDER BY clauses to be used as WHERE clauses when using a cursor, and it only accepts strings (i.e. column names).

I tried adding a SELECT (title FROM metadata WHERE...) as metadata_title and then ORDER BY metadata_title but that does not work because MySQL can not use WHERE on such a 'fake' column.

And I also tried adding a leftJoin('metadata', ...) but that messes up the Eloquent relationship loading.

I know it's quite a generic problem, but because this package works so nice for many other aspects I am hoping someone has been dealing with a similar issue and found a solution.