Add a findAll that takes a Pageable and returns a Slice instead of a Page

[simasch]

The PagingAndSortingRepository has a Page<T> findAll(Pageable pageable) method.

The problem is that returning a Page will result in a count and a select statement.

The same problem is present in JpaSpecificationExecutor. So it would be awesome to have this covered as well.

[vladmihalcea]

So, should we define findAll that returns a Slice instead?

One option would be to avoid extending any base interface and create additional interfaces that provide this extra functionality:

• PagingBaseJpaRepository
• SlicingBaseJpaRepository

[simasch]

+1 for the additional interfaces

[josergdev]

@vladmihalcea @simasch Can't this be achieved using JpaSpecificationExecutor::findBy method?

<S extends T, R> R findBy(Specification<T> spec, Function<FluentQuery.FetchableFluentQuery<S>, R> queryFunction);

I created this gist: https://gist.github.com/josergdev/06c82891a719eca4834410339885ad23

package dev.joserg.jpa;

import static org.springframework.data.domain.ScrollPosition.offset;

import java.util.function.Function;

import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.ScrollPosition;
import org.springframework.data.domain.Slice;
import org.springframework.data.domain.SliceImpl;
import org.springframework.data.domain.Sort;
import org.springframework.data.domain.Window;
import org.springframework.data.jpa.domain.Specification;
import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
import org.springframework.data.repository.query.FluentQuery.FetchableFluentQuery;

public interface SliceSpecificationExecutor<T> extends JpaSpecificationExecutor<T> {

  default Window<T> findAllWindowed(Specification<T> spec, Sort sort, int limit, ScrollPosition scrollPosition) {
    return this.findBy(spec, toWindow(sort, limit, scrollPosition));
  }

  default Window<T> findAllWindowed(Specification<T> spec, Sort sort, ScrollPosition scrollPosition) {
    return this.findBy(spec, toWindow(sort, scrollPosition));
  }

  default Window<T> findAllWindowed(Specification<T> spec, ScrollPosition scrollPosition) {
    return this.findAllWindowed(spec, Sort.unsorted(), scrollPosition);
  }

  default Slice<T> findAllSliced(Specification<T> spec, Pageable pageable) {
    final var window = pageable.isUnpaged()
        ? this.findAllWindowed(spec, pageable.getSort(), offset())
        : this.findAllWindowed(spec, pageable.getSort(), pageable.getPageSize(), this.getInclusiveStartingOffset(pageable));
    return new SliceImpl<>(window.getContent(), pageable, window.hasNext());
  }

  private ScrollPosition getInclusiveStartingOffset(Pageable pageable) {
    return pageable.getOffset() == 0
        ? ScrollPosition.offset()
        : offset(pageable.getOffset() - 1);
  }

  private static <T> Function<FetchableFluentQuery<T>, Window<T>> toWindow(Sort sort, int limit, ScrollPosition scrollPosition) {
    return fetchableFluentQuery -> fetchableFluentQuery.sortBy(sort).limit(limit).scroll(scrollPosition);
  }

  private static <T> Function<FetchableFluentQuery<T>, Window<T>> toWindow(Sort sort, ScrollPosition scrollPosition) {
    return fetchableFluentQuery -> fetchableFluentQuery.sortBy(sort).scroll(scrollPosition);
  }

}

EDIT:
Since Spring Data 3.3.3, OffsetScrollPosition is exclusive starting point.
https://github.com/spring-projects/spring-data-commons/wiki/Spring-Data-2024.0-Release-Notes#behavior-changes-in-offset-based-scrolling

Behavior Changes in Offset-based Scrolling
Scrolling behavior using offsets has been aligned with keyset-based scrolling. Both implementations now treat a given ScrollPosition as an exclusive starting point. It is important to start scrolling with the initial position ScrollPosition.offset() or ScrollPosition.keyset() to ensure the first element is included in the result. Scrolling from ScrollPosition.offset(0) will resume scrolling after the first element.

[vladmihalcea]

@josergdev Thanks for the tip.

[abuzar-aftab]

Is this done?

[vladmihalcea]

@abuzar-aftab Be the change you want to see in this world and provide a Pull Request with the fix.