是什么导致了这个retainAll异常？

发布于 2024-09-02 12:49:08 字数 1621 浏览 6 评论 0原文

java.lang.UnsupportedOperationException: This operation is not supported on Query Results
    at org.datanucleus.store.query.AbstractQueryResult.contains(AbstractQueryResult.java:250)
    at java.util.AbstractCollection.retainAll(AbstractCollection.java:369)
    at namespace.MyServlet.doGet(MyServlet.java:101)

我试图获取从数据存储查询中检索到的一个列表，并仅保留从键列表中检索到的列表中的结果。我的两个列表都按预期填充，但我似乎无法在其中任何一个上使用retainAll。

//           List<Data> listOne = new ArrayList(query.execute(theQuery));
//           DatastoreService ds = DatastoreServiceFactory.getDatastoreService();
//           List<Data> listTwo = new ArrayList(ds.get(keys).values());
//           listOne.retainAll(listTwo);

编辑

好吧，为了简化，因为这显然是多个问题合而为一，我已经停止使用数据存储的低级 API，而不是只是用循环一一拉动。

                List<MyClass> test = (List<MyClass>) query.execute();
                List<MyClass> test2 = new ArrayList<MyClass>();

                for (String key : favorites) {
                    test2.add(pm.getObjectById(MyClass.class, key));
                }

                log.info(test.toString());
                test.retainAll(test2);

以上有效。它不会抛出异常。下面确实抛出异常。唯一的区别是 log.info。我很困惑。

                List<MyClass> test = (List<MyClass>) query.execute();
                List<MyClass> test2 = new ArrayList<MyClass>();

                for (String key : favorites) {
                    test2.add(pm.getObjectById(MyClass.class, key));
                }

                test.retainAll(test2);

原文

java.lang.UnsupportedOperationException: This operation is not supported on Query Results
    at org.datanucleus.store.query.AbstractQueryResult.contains(AbstractQueryResult.java:250)
    at java.util.AbstractCollection.retainAll(AbstractCollection.java:369)
    at namespace.MyServlet.doGet(MyServlet.java:101)

I'm attempting to take one list I retrieved from a datastore query, and keep only the results which are also in a list I retrieved from a list of keys. Both my lists are populated as expected, but I can't seem to user retainAll on either one of them.

//           List<Data> listOne = new ArrayList(query.execute(theQuery));
//           DatastoreService ds = DatastoreServiceFactory.getDatastoreService();
//           List<Data> listTwo = new ArrayList(ds.get(keys).values());
//           listOne.retainAll(listTwo);

EDIT

Ok, in an attempt to simplify, since this is apparently multiple problems in one, I have stopped using the low level API for datastore and instead of am just pulling one by one with a loop.

                List<MyClass> test = (List<MyClass>) query.execute();
                List<MyClass> test2 = new ArrayList<MyClass>();

                for (String key : favorites) {
                    test2.add(pm.getObjectById(MyClass.class, key));
                }

                log.info(test.toString());
                test.retainAll(test2);

The above works. It doesn't throw the exception. The below does throw the exception. The only difference is the log.info. I'm stumped.

                List<MyClass> test = (List<MyClass>) query.execute();
                List<MyClass> test2 = new ArrayList<MyClass>();

                for (String key : favorites) {
                    test2.add(pm.getObjectById(MyClass.class, key));
                }

                test.retainAll(test2);

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蓝眸 2024-09-09 12:49:08

它不会让我对查询结果执行 new ArrayList()，因为它返回一个对象数组。

但是，您需要将它们放入 new ArrayList() 中。返回的List实现显然不支持retainAll()。这就是例外告诉你的。

“普通”ArrayList 支持它。如果由于泛型类型的差异而无法通过 ArrayList 构造函数，那么您需要手动循环它并在添加之前强制转换每个项目。

List<Data> listTwo = new ArrayList<Data>();
for (Object object : ds.get(keys).values()) {
    listTwo.add((Data) object);
}
listOne.retainAll(listTwo);

更新：根据您的更新，实体显然是延迟加载/填充的。大多数 ORM（DataNucleus 就是其中之一）确实可以这样做。由于我不使用 DataNucleus，因此我无法详细说明如何以“好的”方式修复该问题。但你至少现在知道了问题的根本原因，并且可以按照上面的方法解决。同样在循环中填充列表 test。

It will not let me do new ArrayList() on the query result since it returns an array of objects.

You however need to put them in a new ArrayList(). The returned List implementation apparently doesn't support retainAll(). That's what the exception is telling you.

A "plain" ArrayList supports it. If passing through the ArrayList constructor is not possible due to difference in generic type, then you'll need to manually loop over it and cast each item before adding.

List<Data> listTwo = new ArrayList<Data>();
for (Object object : ds.get(keys).values()) {
    listTwo.add((Data) object);
}
listOne.retainAll(listTwo);

Update: as per your update, the entities are apparently lazily loaded/filled. Most ORM's (DataNucleus is one) may indeed do that. As I don't use DataNucleus, I can't go in detail how to fix that in a "nice" way. But you at least now know the root cause of the problem and it can be solved the same way as above. Fill the list test in a loop as well.

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