Converting CallbackDataProvider offset and limit to Pageable page and size

Question

I have an existing REST service that accepts PAGE and SIZE parameters

/fetchrecords?page=0&size=10

which in turn, creates a Spring Pageable to be used with Spring Repository.

Pageable pageRequest = new PageRequest(page, size, Sort.Direction.DESC, "created");

I want to now use Vaadin 8 CallbackDataProvider, however it produces OFFSET and LIMIT to be used for the BackendDataProvider.

dataProvider = new CallbackDataProvider<MyPojo, Void>(
                    query -> service.fetchrecords(query.getOffset(), query.getLimit()).stream(),
                    query -> service.getCount());

Of course this won't work as offset != page, and limit value will change based on how many records are left, according to the offset position.

Without rewriting the rest/service, how can I go from the DataProvider OFFSET and LIMIT to PAGE and SIZE, correctly?

Answer 1

I had the same problem. The Vaadin paging with offset and limit is more powerful than paging with page and page size (as in your REST service and in spring class PageRequest). So, the answer to your question is: you can't easily. If you could change your REST service parameters to offset and limit then you can implement your own Pageable like:

public class Range implements Pageable, Serializable {

    private static final long serialVersionUID = 0L;

    private int limit;
    private long offset;
    private Sort sort;

    public Range(long offset, int limit, Sort sort) {
         ...
    }

    @Override
    public long getOffset() {
        return offset;
    }

    ...

}

I wonder why this isn't available out-of-the-box.

Another option is to map the offset/limit to possibly multiple pages that include the required range of data, then get these pages and take only the necessary data.

Please note: This is not working for the last page requested by Vaadin when accessing Neo4j via Spring Data Neo4j. SDN v5.2.8 will use the following code to apply "skip" to query

parameters.put(SKIP, pageable.getPageNumber() * pageable.getPageSize());

The use of getPageNumber is a problem, e.g. offset 100 and limit 23 results in skip of 92. Filed an issue.