相关疑难解决方法(0)

我必须遵循实体对象

@Entity
public class Foobar {
    ...
    private List<String> uuids;
    ...
}

现在我想制作一个条件查询来获取所有Foobar pojos,其uuids列表包含字符串"abc123",我只是不确定如何制定适当的标准.

我有以下条件构建器查询

    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<Object> critQuery = cb.createQuery();

    Root<Role> role = critQuery.from(Role.class);

    //create a join between role and permission
    MapJoin<Role,String,Permission> perm = role.joinMap("permissions");
    critQuery.multiselect(role.get("label"), perm.key(), perm.value());

    //this line throws NPE
    Query query = em.createQuery(critQuery);

最后一行抛出空指针异常.

java.lang.NullPointerException
at org.hibernate.ejb.criteria.path.AbstractPathImpl.prepareAlias(AbstractPathImpl.java:246)
at org.hibernate.ejb.criteria.path.AbstractPathImpl.render(AbstractPathImpl.java:253)
at org.hibernate.ejb.criteria.path.AbstractPathImpl.renderProjection(AbstractPathImpl.java:261)