问题

我正在尝试创建一个 `javax.persistence.criteria.Predicate`，以便匹配在 `Map<String,String>` 属性中包含特定键/值条目的实体。这是在 Spring Data JPA 和 `JpaSpecificationExecutor<MyEntity>` 存储库的上下文中。

```java
class MyEntity {
  @ElementCollection(fetch = FetchType.EAGER)
  ...
  Map<String, String> metadata = new HashMap<>();
}

static Specification<MyEntity> hasMetadata(String name, String value) {
  return (entity, criteriaQuery, criteriaBuilder) -> {
    Path<Map<String,String>> metadata = entity.get("metadata");

    // fixme: insert magic
    //
    // not quite right: cb.isMember(cb.literal(value), metadata) 

    return ...
  };
}

这里有一个稍微相关的问题 https://stackoverflow.com/questions/13982058/criteriabuilder-and-ismember-of-list-on-entity-hibernate，但我从那里没有获取到太多信息。

一个解决方案会很好，还有一个指向详细说明的文档的指针也会很好。我的 Google 搜索能力不足以找到这方面的信息。

<details>
<summary>英文:</summary>

I&#39;m trying to create a `javax.persistence.criteria.Predicate` to match entities which contain a certain key/value entry in a `Map&lt;String,String&gt;` property. This is in the context of Spring Data JPA and a `JpaSpecificationExecutor&lt;MyEntity&gt;` repository.

```java
class MyEntity {
  @ElementCollection(fetch = FetchType.EAGER)
  ...
  Map&lt;String, String&gt; metadata = new HashMap&lt;&gt;();
}

static Specification&lt;MyEntity&gt; hasMetadata(String name, String value) {
  return (entity, criteriaQuery, criteriaBuilder) -&gt; {
    Path&lt;Map&lt;String,String&gt;&gt; metadata = entity.get(&quot;metadata&quot;);

    // fixme: insert magic
    //
    // not quite right: cb.isMember(cb.literal(value), metadata) 

    return ...
  };
}

There is a slightly related question https://stackoverflow.com/questions/13982058/criteriabuilder-and-ismember-of-list-on-entity-hibernate, but I haven't been able to glean much info from there.

A solution would be nice, but also a pointer to documentation where this is specified too. My Google-fu is failing me.

答案1

得分: 2

我在这里找到了一个非常相似的问题：https://stackoverflow.com/questions/5580614/jpa-criteriabuilder-join-maps，其中提供了一个看起来现在可以工作的解决方案：

static Specification<MyEntity> hasMetadata(String name, String value) {
  return (entity, criteriaQuery, criteriaBuilder) -> {
    MapJoin<MyEntity, String, String> join = entity.joinMap("metadata");
    return criteriaBuilder.and(
      criteriaBuilder.equal(join.key(), name),
      criteriaBuilder.equal(join.value(), value)
    );
  };
}

static Specification<MyEntity> hasMetadata(String name, String value) {
  return (entity, criteriaQuery, criteriaBuilder) -> {
    MapJoin<MyEntity, String, String> join = entity.joinMap("metadata");
    return criteriaBuilder.and(
      criteriaBuilder.equal(join.key(), name),
      criteriaBuilder.equal(join.value(), value)
    );
  };
}