Google App Engine / Java - ORDER BY 不一致
我在 App Engine 之上使用 JPA（我对两者都很陌生），目前我面临着一种我不理解的行为。
每次刷新页面时，获取的项目的顺序都会发生变化。
以下是代码片段：
Set<Cast> results = new HashSet<Cast>();
EntityManager entityManager = entityManagerFactory.createEntityManager();
Query query = entityManager.createQuery(FIND_ALL_SORTED_BY_DESCENDING_BROADCAST_DATE);
@SuppressWarnings("unchecked")
List<Cast> casts = query.getResultList();
for (Cast cast : casts) {
if (verifySecondaryFields(cast)) {
results.add(synchronizeTechnicalFields(cast));
}
}
entityManager.close();
return Collections.unmodifiableSet(results);
其中 FIND_ALL_SORTED_BY_DESCENDING_BROADCAST_DATE 实际上是 SELECT cast FROM Cast cast ORDER BY cast.broadcastDate DESC。
entityManagerFactory 是我的存储库类的自动装配成员。
问题是 ORDER BY 子句似乎被忽略，结果随机显示。你能发现哪里出了问题吗？
I am using JPA on top of App Engine (I am quite new to both) and I am currently facing a behaviour I do not understand.
Each time I refresh the page, the order of the fetched items changes.
Here is the code snippet:
Set<Cast> results = new HashSet<Cast>();
EntityManager entityManager = entityManagerFactory.createEntityManager();
Query query = entityManager.createQuery(FIND_ALL_SORTED_BY_DESCENDING_BROADCAST_DATE);
@SuppressWarnings("unchecked")
List<Cast> casts = query.getResultList();
for (Cast cast : casts) {
if (verifySecondaryFields(cast)) {
results.add(synchronizeTechnicalFields(cast));
}
}
entityManager.close();
return Collections.unmodifiableSet(results);
where FIND_ALL_SORTED_BY_DESCENDING_BROADCAST_DATE actually is SELECT cast FROM Cast cast ORDER BY cast.broadcastDate DESC.
entityManagerFactory is an autowired member of my repository class.
The thing is the ORDER BY clause seems to be ignored and the results show up randomly. Can you spot what is wrong?
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集合不保持顺序。列表可以。尝试
List= new ArrayList(); 并从那里继续。Sets don't preserve order. Lists do. Try
List<Cast> = new ArrayList<Cast>();and carry on from there.