JPA 标准检索项目和计数

Question

我需要使用 JPA Criteria API 从格式的数据中返回摘要

“不同值” -> 不同值的计数

    CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
    CriteriaQuery<Tuple> criteriaQuery = criteriaBuilder.createQuery(Tuple.class);
    Root<User> root = criteriaQuery.from(User.class);

    // this is where I want to get a count of the user levels and how many users per level
    criteriaQuery.select(criteriaBuilder.tuple(
        root.get(User_.userLevel),
        // user count?
    ));

我更喜欢通过条件 API 执行此操作。

谁能帮忙？

杰森

Answer 1

这应该可以解决问题：

CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<Tuple> tupleQuery = cb.createTupleQuery();
Root<User> root = tupleQuery.from( User.class );

tupleQuery
  .select( cb.tuple( root.get( User_.userLevel ), cb.distinctCount( root ) ) )
  .groupBy( root.get( User_.userLevel ) );

List<Tuple> results = entityManager.createQuery( tupleQuery ).getResultList();