Primefaces LazyDataModel：（过时）

Question

我有一个巨大的对象列表，每个对象都包含许多图像。我想使用延迟加载来部分获取它们。我想了解如何使用 LazyDataModel 及其工作原理。

最初我认为我只需要在LazyDataModel 中保存可能获取的对象的ID。和当负载（）方法调用-我不得不从DB获取的图像和替代数据源与取出的数据。所以每次我想加载更多数据时，我都会运行查询。

private List<MyEntity> datasource; // contains only ids of MyEntity

@Override

public List<MyEntity> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String,Object> filters) {

    //rowCount

    int dataSize = datasource.size();

    this.setRowCount(dataSize);

    //get listOfIdToFetch

    //paginate

    datasource = datasource.addAll(myJpaRepository.findByIds(listOfIdToFetch));

    return datasource;

}

我无法让它工作，因为 primefaces 使用了 lock() 方法并在应该加载新的数据部分时抛出异常：

org.springframework.webflow.conversation.impl.LockTimeoutException：30 秒后无法获取对话锁

最后我明白了 LazyDataModel 的 primefaces 示例（其中保存到datasource的完整数据列表，包括所有图像）可能是正确的使用方式。因为最初我认为它是简化的虚拟示例，在实际项目中我将使用 sql 查询来部分地获取图像。

private List<MyEntity> datasource; // contains all images of all records

@Override

public List<MyEntity> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String,Object> filters) {

    //rowCount

    int dataSize = datasource.size();

    this.setRowCount(dataSize);

    //paginate

    return datasource.subList(first, first + pageSize);

}

我想了解 LazyDataModel 如何工作并提高性能。如果使用这种方法的正确方法是从 DB 检索所有数据并将其保存到datasource。Primefaces 是否将这些数据保存在服务器上并部分刷新？如果 sql 结果包含数千张图像，我应该寻找不同的方法并设置检索记录的限制吗？如何实现最佳的延迟加载性能提升？或者也许最初的方法是正确的，我应该调查为什么会发生这个错误？

Answer 1

好的，我终于做到了，每次 load() 方法被触发时我都应该执行查询的想法是正确的。我面临的问题：如果我只返回查询的结果 -&nbsp;load() 方法只触发一次，并且我无法加载更多数据。所以我使用虚拟sublist(0, chunkSize)。我不能@Autowire 我的存储库，我有一个例外，说某些对象未序列化。但是我可以使用 EntityManager而这就是我所做的。源代码：private List<MyEntity> datasource; // contains only ids@Overridepublic List<MyEntity> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String,Object> filters) {&nbsp; &nbsp; &nbsp; &nbsp; StringBuilder queryText = new StringBuilder("select ...");&nbsp; &nbsp; &nbsp; &nbsp; List<MyEntity> list;&nbsp; &nbsp; &nbsp; &nbsp; //paginate&nbsp; &nbsp; &nbsp; &nbsp; if(datasource.size() > pageSize) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; try {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; list = new ArrayList<>(datasource.subList(first, first + pageSize));&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; catch(IndexOutOfBoundsException e) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; list = new ArrayList<>(datasource.subList(first, first + (datasource.size() % pageSize)));&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; else {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; list = new ArrayList<>(datasource);&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; boolean setComa = false;&nbsp; &nbsp; &nbsp; &nbsp; for (MyEntity a: list) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (setComa) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; queryText.append(","+a.getId());&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; queryText.append(a.getId());&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; setComa = true;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; queryText.append(")");&nbsp; &nbsp; &nbsp; &nbsp; Query q = em.createQuery(queryText.toString());&nbsp; &nbsp; &nbsp; &nbsp; list = q.getResultList();&nbsp; &nbsp; &nbsp; &nbsp; return list.subList(0, list.size());}更新限制：@Overridepublic List<MyEntity> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String,Object> filters) {&nbsp; &nbsp; List<MyEntity> list;&nbsp; &nbsp; Query q = em.createQuery(this.queryText);&nbsp; &nbsp; // Paginate&nbsp; &nbsp; q.setFirstResult(first);&nbsp;&nbsp; &nbsp; q.setMaxResults(pageSize);&nbsp;&nbsp; &nbsp; list = query.getResultList();&nbsp; &nbsp; return list.subList(0,list.size());}