QueryDsl SpringData Jpa findAll如何避免count（）

Question

在任何情况下，我不想重复计数的每一个页面我需要，这个信息是需要的只是第一次调用。

Answer 1

基于Ali Dehghani的回答，我们为querydsl 4.2.1构建了以下内容，因为querydsl语法在当前版本4.x中发生了变化

存储库接口：

import com.querydsl.core.types.EntityPath;
import com.querydsl.core.types.Predicate;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Slice;

public interface SliceableRepository<T> {

  Slice<T> findAllSliced(EntityPath<T> entityPath, Predicate predicate, Pageable pageable);
}

存储库实现:
（必须命名为“ impl”）

import com.querydsl.core.types.EntityPath;
import com.querydsl.core.types.Predicate;
import com.querydsl.core.types.dsl.PathBuilder;
import com.querydsl.jpa.JPQLQuery;
import com.querydsl.jpa.impl.JPAQuery;
import com.querydsl.jpa.impl.JPAQueryFactory;
import java.util.List;
import javax.persistence.EntityManager;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Slice;
import org.springframework.data.domain.SliceImpl;
import org.springframework.data.jpa.repository.support.Querydsl;


public class SliceableRepositoryImpl<T> implements SliceableRepository<T> {

  private final EntityManager entityManager;
  private final JPAQueryFactory jpaQueryFactory;

  public SliceableRepositoryImpl(EntityManager entityManager) {
    this.entityManager = entityManager;
    this.jpaQueryFactory = new JPAQueryFactory(entityManager);
  }

  @Override
  public Slice<T> findAllSliced(final EntityPath<T> entityPath, final Predicate predicate,
      final Pageable pageable) {

    final Querydsl querydsl = new Querydsl(entityManager,
        new PathBuilder<>(entityPath.getType(), entityPath.getMetadata()));

    final int oneMore = pageable.getPageSize() + 1;

    final JPAQuery<T> query = this.jpaQueryFactory.selectFrom(entityPath)
        .where(predicate)
        .offset(pageable.getOffset())
        .limit(oneMore);

    final JPQLQuery<T> querySorted = querydsl.applySorting(pageable.getSort(), query);

    final List<T> entities = querySorted.fetch();

    final int size = entities.size();
    // If there was one more result than requested from the pageable,
    // then the slice gets "hasNext"=true
    final boolean hasNext = size > pageable.getPageSize();
    if (hasNext) {
      entities.remove(size - 1);
    }
    return new SliceImpl<>(entities, pageable, hasNext);
  }
}

public SomeRepository extends JpaRepository<Some, Long>, SliceableRepository<Some> {
}

public class MyService {
  @Autowired
  private final SomeRepository someRepository;

  public void doSomething() {
    Predicate predicate = ...
    Pageable pageable = ...
     // QSome is the generated model class from querydsl
    Slice<Some> result = someRepository.findAllSliced(QSome.some, predicate, pageable);
  }
}