How to count the number of rows of a JPA 2 CriteriaQuery in a generic JPA DAO?

[ramin iramin]

I'm new in JPA and want to implement a generic JPA DAO and need to find the number of rows of a query result set to implement pagination. After searching the web, I can't find a practical way to do that. Here is the code suggested in many articles:

    public <T> Long findCountByCriteria(CriteriaQuery<?> criteria) {
        CriteriaBuilder builder = em.getCriteriaBuilder();
    
        CriteriaQuery<Long> countCriteria = builder.createQuery(Long.class);
        Root<?> entityRoot = countCriteria.from(criteria.getResultType());
        countCriteria.select(builder.count(entityRoot));
        countCriteria.where(criteria.getRestriction());
    
        return em.createQuery(countCriteria).getSingleResult();
    }

However, that code doesn't work when using `join`. Is there any way to count the rows of a query result set using the JPA Criteria API?



here is the code that create CriteriaQuery :

		CriteriaQuery<T> queryDefinition = criteriaBuilder.createQuery(this.entityClass);
		Root<T> root = queryDefinition.from(this.entityClass);

and some joins may be added to the root until the query have been executed:

    public Predicate addPredicate(Root<T> root) {
    				Predicate predicate = getEntityManager().getCriteriaBuilder().ge(root.join(Entity_.someList).get("id"), 13);
    				return predicate;
    }

and the generated exception is like :

> org.hibernate.hql.ast.QuerySyntaxException: Invalid path:
> 'generatedAlias1.id' [select count(generatedAlias0) from entity.Entity
> as generatedAlias0 where ( generatedAlias0.id>=13L ) and (
> (generatedAlias1.id<=34L ) )]


which generatedAlias1 should be on Entity and generatedAlias0 should be on the association that I joined on that.
Note that I implement Join properly because when I execute query without count query it executes without error and the Join works properly but when I try to execute count query it throws exception.