Add support for `Window` scrolling queries

[chrisbuettgen]

Hi there,
originally I was working with Spring for GraphQL when I stumbled upon this problem:

I wanted to perform a query with a Reactive Repository returning a windowed result, but it would complain about a "non unique result". Most likely because the return type of the Repsitory method is Mono<Window<Book>> (I need the Window for GraphQL), but the query itself returns several rows.

interface BookRepository : ReactiveCrudRepository<Book, Long>, ReactiveQueryByExampleExecutor<Book> {

    fun findAllByOrderByName(example: Example<Book>, position: ScrollPosition): Mono<Window<Book>>

}

Am I missing something, or does Window not work in a Reactive context (yet)?

Find the attached source code with a Unit test to illustrate the problem.
reactive_window_query.zip

[mp911de]

Spring Data R2DBC does not yet support keyset scrolling. This is something we want to implement in the future.

[mzvankovich]

Spring Data R2DBC does not yet support keyset scrolling. This is something we want to implement in the future.

Hello @mp911de does Spring Data R2DBC still not support offset/keyset scrolling? How can it be properly used for ReactiveCrudRepository? I'm particularly interested in getting it to work for r2dbc-postgresql driver. Thanks.