Jpa标准计数

Question

我有新问题。我创建了一些代码，从客户端请求中生成谓词。这是初始化部分：

criteriaBuilder = entityManager.getCriteriaBuilder(); 
criteriaQuery = criteriaBuilder.createQuery(classEntity); 
root = criteriaQuery.from(classEntity); 

时，我想拿到名单的实体它工作的伟大：

criteriaQuery.select(root).where(predicate); 
entityManager.createQuery(criteriaQuery).getResultList(); 

但是，当我想指望实体：

CriteriaQuery<Long> cq = criteriaBuilder.createQuery(Long.class); 
cq.select(criteriaBuilder.count(root)).where(predicate); 
System.err.println("eee : " +entityManager.createQuery(cq).getSingleResult()); 

它例外

下降

java.lang.IllegalArgumentException: Error occurred validating the Criteria Caused by: java.lang.IllegalStateException: No criteria query roots were specified

也许我应该说，这根生成动态加入：

private Path parseField(String field) { 
    Path path = null; 

    if (field.contains(".")) { 

     String [] split = field.split("\\."); 
     Join join = root.join(split[0],JoinType.INNER); 

     for (int i =1; i < split.length-1; i++) { 
      join = join.join(split[i],JoinType.INNER); 
     } 

     path = join.get(split[split.length-1]); 

    } else { 
     path = root.get(field); 
    } 
    return path; 
} 

如果我更换

cq.select(criteriaBuilder.count(root)).where(previousPredicate); 

上

cq.select(criteriaBuilder.count(cq.from(classEntity))).where(previousPredicate); 

我会失败，出现异常

org.hibernate.hql.ast.QuerySyntaxException: Invalid path: 'generatedAlias1.(someFieldName)' 

Answer 1

这一切工作正常，我：

CriteriaBuilder cb = em.getCriteriaBuilder(); 
CriteriaQuery<Long> q = cb.createQuery(Long.class); 
Root<A> r = q.from(A.class); 
MapJoin<A, String, String> m = r.joinMap("metadata"); 
q.select(cb.count(r)).where(cb.equal(m.key(), "A")); 
Long rs = em.createQuery(q).getSingleResult(); 

因此，很难看到你做错了没有MCVE什么。