在春季使用实体管理器实现分页 [英] Implementing Pagination using entity manager in spring

问题描述

如何在Spring + Hibernate项目中实现分页? 以下是代码.我将获得PageRequest对象，并想返回项目的页面

How can I implement pagination in Spring + hibernate project ? Following is the code. I will get PageRequest object and I want to return Page of item

 @Repository
    public class ItemRepository {

      @PersistenceContext
      EntityManager entityManager;

      public Page<Item> findItems(PageRequest pageRequest) {
        // TODO: Implement me
        return new Page<>(new ArrayList<>(), 0, 0);
      }
    }


    public class PageRequest {

      private final int count;
      private final int pageNumber;

      public PageRequest(int pageNumber, int count) {
        assert pageNumber >= 0;
        assert count > 0;

        this.pageNumber = pageNumber;
        this.count = count;
      }

      public int getCount() {
        return count;
      }

      public int getPageNumber() {
        return pageNumber;
      }
    }

推荐答案

我找到了解决方法

public Page<Item> findItems(PageRequest pageRequest) {

    Query query = entityManager.createQuery("From Item");
    int pageNumber =pageRequest.getPageNumber();
    int pageSize = pageRequest.getCount();
    query.setFirstResult((pageNumber) * pageSize);
    query.setMaxResults(pageSize);
    List <Item> fooList = query.getResultList();

    Query queryTotal = entityManager.createQuery
            ("Select count(f.id) From Item f");
    long countResult = (long)queryTotal.getSingleResult();
    int i=(int)countResult;
    return new Page<>(fooList, pageRequest.getPageNumber(),i);
  }

我不得不向数据库查询两次，一次获取记录，然后获取所有计数

I had to query two times to DB once to get records and then to get all the count

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