通过集合集选择实体 [英] Selecting an entity by collection set equality

问题描述

我正在尝试执行以下操作的JPQL查询或JPA操作。我有一个元素，由一个字符串的元素集合组成：

I'm trying to do a JPQL query or JPA operation that does the following. I have an element, that consist of an element collection of Strings:

@Entity(name="REQUEST")
public class Request {

    @ElementCollection
    private Set<String> keywords;
    ...    
}

我希望能够选择实体whos关键字与给定的字符串集完全匹配。我已经研究过使用IN但是如果只存在一个关键字则匹配。如果所有关键字都存在，我该如何匹配？

I want to be able to select the entity whos keywords exactly matches a given Set of strings. I've looked into using IN but that will match if only one keyword exists. How do I match only if all keywords exist?

推荐答案

我能想到的最简单的方法是做两个计数查询： / p>

The simplest approach I can think of is to do two count queries:

1. 集合中关键字数量的计数


2. 关键字数量的计数NOT在集合中

＃1的结果应该等于集合中的关键字数量。 ＃2的结果应该等于0.例如：

The result of #1 should equal the number of keywords in the set. The result of #2 should equal 0. For example:

List<Request> requests = 
  em.createQuery("select r from Request r " +
                 "where (select count(k1) from Request r1 " +
                 "       join r1.keywords k1 " +
                 "       where r1 = r and k1 in :keywords) = :numKeywords " +
                 "and (select count(k2) from Request r2 " +
                 "     join r2.keywords k2 " +
                 "     where r2 = r and k2 not in :keywords) = 0", Request.class)
     .setParameter("keywords", keywords)
     .setParameter("numKeywords", keywords.size())
     .getResultList();

如果您关心的是该集合是否是请求关键字的子集，那么不需要第二次计数。这可以通过以下方式在一个查询中完成：

If all you cared about was whether or not the set is a subset of the Request's keywords, then the second count is not needed. This can be done in a single query with a group by:

List<Request> requests = 
      em.createQuery("select r from Request r " +
                     "join r.keywords k " +
                     "where k in :keywords " +
                     "group by r " +
                     "having count(r) = :numKeywords", Request.class)
        .setParameter("keywords", keywords)
        .setParameter("numKeywords", keywords.size())
        .getResultList();

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