从休眠选择查询获取结果计数（查询返回的对象不是选择计数（*））

Question

I am having an HQL query

String q = "From TMainTable where a= ? and b= ? and c=?"
Query q = session.createQuery(q).setParameter(0,1).setParameter(1,2).setParameter(2,3);
int count = getCount(q);
List<TMainTable> list = q.setFirstResult(pageNo).setMaxResults(maxLimit).list()

public int getCount(Query q){
   return q.list().size();
}

But the getCount method is taking so much of time. Say my table has 10000 rows and I am getting only 20 records at a time with the actual count. What is the fastest method to get count using the Query object.

I have tried this in the getCount function

public Long getCount(Query q){
String queryString = q.getQueryString();
            String countQueryString = "Select count(*) From "+queryString.substring(0, q.getQueryString().indexOf(" From"));
            System.out.println(countQueryString);
            Long c= (Long)ctx.getSession().createQuery(countQueryString).uniqueResult();
return c;
}

But how can I set the parameters in the new query ? Is there a way I can alter only the query string in Query Object.

Answer 1

You have to set parameters starting with 1 not with 0 :

Query q = session.createQuery(q).setParameter(0,1).setParameter(1,2).setParameter(2,3);
//--------------------------------------------^-----------------^-----------------^

Instead you have to use :

Query q = session.createQuery(q).setParameter(1,1).setParameter(2,2).setParameter(3,3);
//--------------------------------------------^-----------------^-----------------^

---

Second to get size of your list, you can use getResultList().size like this :

public int getCount(Query q){
   return q.getResultList().size();
}

Answer 2

You should see what kind of sql is generated by hibernate. It can be very inefficient. If so you should write native sql query.

Answer 3

Conventionally, you would have two queries, one to do a count(*) formally, and a second for the actual query. The only way that the main query can get the number of results is by fully executing and then doing a count on the result list, which will be very slow.

Answer 4

Try this out :

  Query query = session.createQuery("select count(*) from Class_NAME as a where YOUR_CONDITION");
        try {
            return Integer.valueOf(String.valueOf(query.uniqueResult()));
        } catch (Exception e) {
            //Print stacktrace
            return 0;
        }