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(), offset(pageable.getOffset()));
    return new SliceImpl<>(window.getContent(), pageable, window.hasNext());
  }

  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);
  }

}

[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.