Support pagination return values and pagination requests in `@SchemaMapping` methods

[rstoyanchev]

When a controller method returns Page we should adapt that to graphql.relay.Connection. Likewise, we should support Pageable as a controller method argument, initialized from GraphQL input arguments.

As part of that we'll need a strategy to encode and decode a cursor. This includes indicating sort order, even if the relay spec does not specify how to do that.

[mladenjotanovichtec]

Hi @rstoyanchev, based on our previous discussion for Pageable and @SortDefaults, it would be
really great that we can annotate Pageable method argument with that annotation and that specified
values are injected into Pageable instance. I am referring to Pageable resolver and support for Sort resolver.

Also, I would like to contribute for the first time in the project so this could be the place for that, what are your thoughts?

[rstoyanchev]

We have worked with the Spring Data team to enable support for keyset and offset based scrolling through a result set, see spring-projects/spring-data-commons#2787. Now that it is available in snapshots, we've been able to both provide feedback to the Spring Data team, and to use the new API for GraphQL pagination.

The main new concepts are Window and ScrollPosition, see "Scrolling" for an introduction. We will provide support for Window and Slice as a return value from from any DataFetcher, and adapting it to graphql.relay.Connection. We'll also support ScrollPosition as a cursor for pagination, and allow injecting the ScrollPosition, number of elements requested, and sort information into a controller method.

[rstoyanchev]

@mladenjotanovichtec, apologies for the slow response, and thanks for the offer to help! As per my previous comment, Spring Data support has added new features for pagination, and we have evolved our plans accordingly. At the moment we are a bit too close to M1, and busy wrapping up, but there will be plenty of opportunities to contribute. We'll make an effort to call them out, but feel free to reach out as well. In the mean time we really do appreciate feedback on the new and existing features.