Spring Data JPA 分页 HHH000104

Question

我得到了这个存储库代码：

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@Query(value = "select distinct r from Reference r " +\n        "inner join fetch r.persons " +\n        "left outer join fetch r.categories " +\n        "left outer join fetch r.keywords " +\n        "left outer join fetch r.parentReferences",\n        countQuery = "select count(distinct r.id) from Reference r " +\n                "inner join r.persons " +\n                "left outer join r.categories " +\n                "left outer join r.keywords " +\n                "left outer join r.parentReferences")\nPage<Reference> findsAllRelevantEntries(Pageable pageable);\n

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当我对该查询运行测试时，我收到此 Hibernate 警告：
\nHHH000104: firstResult/maxResults specified with collection fetch; applying in memory!

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@Test\nvoid testFindAllRelevantAsync() throws ExecutionException, InterruptedException {\n    CompletableFuture<Page<Reference>> all = referenceService.findAllRelevantAsync(PageRequest.of(1, 20));\n    CompletableFuture.allOf(all).join();\n    assertThat(all.get()).isNotNull();\n    assertThat(all.get()).isNotEmpty();\n}\n

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存储库代码封装在此处未显示的服务方法中。它（服务方法）只是将服务的调用编组到存储库并返回。

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此外，生成的 sql 查询不会生成limit子句。尽管它确实引发了两个查询。

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一个用于count，另一个用于获取所有记录。
\n因此它会获取所有记录并在内存中应用分页。
\n这会导致查询执行速度非常慢。

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我怎样才能使分页与此查询一起使用？

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编辑

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我知道这里经常建议作为解决方案：\n如何避免警告“使用集合获取指定的firstResult/maxResults；在内存中应用！” 当使用休眠时？

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有没有办法使用 Spring Data JPA 实现分页？\n我不想\xc2\xb4t 想要硬连线 an EntityManager，也不想\n从 a 扩展代码BasicTransformerAdapter

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Answer 1

我自己找到了解决方法。基于此：
如何避免警告“使用集合获取指定的firstResult/maxResults；在内存中应用！” 当使用休眠时？

首先：通过分页获取Id：

@Query(value = "select distinct r.id from Reference r " +
        "inner join r.persons " +
        "left outer join r.categories " +
        "left outer join r.keywords " +
        "left outer join r.parentReferences " +
        "order by r.id",
        countQuery = "select count(distinct r.id) from Reference r " +
                "inner join r.persons " +
                "left outer join r.categories " +
                "left outer join r.keywords " +
                "left outer join r.parentReferences " +
                "order by r.id")
Page<UUID> findsAllRelevantEntriesIds(Pageable pageable);

第二：使用Id进行in查询

@Query(value = "select distinct r from Reference r " +
        "inner join fetch r.persons " +
        "left outer join fetch r.categories " +
        "left outer join fetch r.keywords " +
        "left outer join fetch r.parentReferences " +
        "where r.id in ?1 " +
        "order by r.id",
        countQuery = "select count(distinct r.id) from Reference r " +
                "inner join r.persons " +
                "left outer join r.categories " +
                "left outer join r.keywords " +
                "left outer join r.parentReferences ")
@QueryHints(value = {@QueryHint(name = "hibernate.query.passDistinctThrough", value = "false")},
        forCounting = false)
List<Reference> findsAllRelevantEntriesByIds(UUID[] ids);

注意： 我得到的List<Reference不是 a，Pageable所以你必须Pageable自己构建，如下所示：

private Page<Reference> processResults(Pageable pageable, Page<UUID> result) {
    List<Reference> references = referenceRepository.findsAllRelevantEntriesByIds(result.toList().toArray(new UUID[0]));
    return new PageImpl<>(references, pageable, references.size());
}

这看起来不太好，并且执行了两个语句，但它使用 进行查询limit，因此仅获取所需的记录。