JPA 2.0：计数任意CriteriaQuery？

问题描述

我尝试实现以下便利方法：

  / ** 
 *计算结果数的搜索。 
 * @param criteria查询的条件。 
 * @return查询的结果数。 
 * / 
 public int findCountByCriteria（CriteriaQuery<？> criteria）; 
  

在Hibernate中，这是通过

  criteria.setProjection（Projections.rowCount（））; 
  

在JPA中相当于上述什么？我发现很多简单的计数示例，但没有一个使用CriteriaQuery的行计数应该确定。

EDIT：

我不幸发现@ Pascal的回答不是正确的。该问题非常微妙，只有当您使用连接时才显示：

  //相同的查询，但可读：
 // SELECT * 
 // From Brain b 
 // WHERE b.iq = 170 
 
 CriteriaQuery< Person> query = cb.createQuery（Person.class）; 
 Root< Person> root = query.from（Person.class）; 
 Join< Object，Object> brainJoin = root.join（brain）; 
 Predicate iqPredicate = cb.equal（brainJoin。< Integer> get（iq），170）; 
 query.select（root）.where（iqPredicate）; 
  

当调用 findCountByCriteria（query）具有以下异常：

  org.hibernate.hql.ast.QuerySyntaxException：无效的路径：'generatedAlias1.iq'[select count（generatedAlias0）from xxx.tests.person.dom.Person as generatedAlias0 where generatedAlias1.iq = 170] 
  

是否有其他方法提供 CountByCriteria 方法？

解决方案

p>我写了一个实用程序类， JpaUtils来做：

• 计数结果：长计数= JpaUtils.count（em，criteriaQuery）;


• copy CriteriaQueries： JpaUtils.copyCriteria（em，criteriaQueryFrom，criteriaQueryTo）;


• 获取计数条件： CriteriaQuery< Long> countCriteria = JpaUtils.countCriteria（em，criteria）

如果您对源代码感兴趣，请参阅

I am trying to implement the following convenience method:

/**
 * Counts the number of results of a search.
 * @param criteria The criteria for the query.
 * @return The number of results of the query.
 */
public int findCountByCriteria(CriteriaQuery<?> criteria);

In Hibernate, this is done by

criteria.setProjection(Projections.rowCount());

What is the equivalent to the above in JPA? I found numerous simple count examples, but none of them made use of a CriteriaQuery whose row count should be determined.

EDIT:

I unfortunately found out that @Pascal's answer is not the correct one. The problem is very subtle and only shows up when you use joins:

// Same query, but readable:
// SELECT *
// FROM Brain b
// WHERE b.iq = 170

CriteriaQuery<Person> query = cb.createQuery(Person.class);
Root<Person> root = query.from(Person.class);
Join<Object, Object> brainJoin = root.join("brain");
Predicate iqPredicate = cb.equal(brainJoin.<Integer>get("iq"), 170);
query.select(root).where(iqPredicate);

When calling findCountByCriteria(query), it dies with the following exception:

org.hibernate.hql.ast.QuerySyntaxException: Invalid path: 'generatedAlias1.iq' [select count(generatedAlias0) from xxx.tests.person.dom.Person as generatedAlias0 where generatedAlias1.iq=170]

Is there any other way to provide such a CountByCriteria method?

解决方案

I wrote a utility class, JDAL JpaUtils to do it:

• count results: Long count = JpaUtils.count(em, criteriaQuery);
• copy CriteriaQueries: JpaUtils.copyCriteria(em, criteriaQueryFrom, criteriaQueryTo);
• get count criteria: CriteriaQuery<Long> countCriteria = JpaUtils.countCriteria(em, criteria)

and so on...

If you are interested in the source code, see JpaUtils.java

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