ORDER BY in Criteria API for a computed column name (by alias)

问题

Having a situation where my java code is symbolic to query -

  SELECT CUSTOMER_ID,
         CUSTOMER_NAME,
         CASE
             WHEN COUNT (DISTINCT CARD_ID) > 1 THEN 'MULTIPLE'
             ELSE MAX(CARD_NUM)
         END    AS CARD_NUM
    FROM CUSTOMER LEFT JOIN CARD ON CARD.CUSTOMER_ID = CUSTOMER.CUSTOMER_ID
GROUP BY CUSTOMER_ID, CUSTOMER_NAME

Java code for detailed info -

CriteriaBuilder cb = em.getCriteriaBuilder();
final CriteriaQuery<Tuple> query = cb.createQuery(Tuple.class);
final Root<Customer> root = query.from(Customer.class);
Expression<Object> caseSelect = cb.selectCase()
        .when(cb.greaterThan(cb.countDistinct(join.get(Card_.cardId)), 1L), "MULTIPLE")
        .otherwise(cb.greatest(Card_.get(Card_.cardNum)));
caseSelect.alias("card_num");
selects.add(caseSelect);
query.multiselect(selects).distinct(true);
query.groupBy(exprs);
query.orderBy(cb.asc(caseSelect));

Now, how to do the order by in Criteria API.

1. If I do orderby root.CARD_NUM, the attribute is not present in Root.- Throws exception.
2. If I do order by the caseSelect expression itself it throws an error stating CARD_ID is not in SELECTED part of query.
3. I cannot have card_num / card_id in select expression, that is not right for the query.

Any way to just order by Alias name? I see Order is Expression type, and how to get an expression from string name. I guess you can do this in Hibernate. Would it be possible to use hibernate orderby in criteria API anyways ? Guess a stupid q

Any help is appreciated.

回答1:

It seems this is not possible with the JPA Criteria API and you will have to fallback to using JPQL/HQL instead.

回答2:

This is fairly not possible and just feels like a case missed by JPA. Though if using hibernate API it is possible. But, my workaround was -

1. Created a view which would contain the case expression.
2. Join the view with my entity (you cannot do a join, but one more query.from(View.class)).
3. In the where add the ids of View and the entity.

Now in the order by you could mention the column name by View.column_name.

来源：https://stackoverflow.com/questions/63082972/order-by-in-criteria-api-for-a-computed-column-name-by-alias