JPA query.getResultList()?

问题

I use JPA 1.0:

Query query;
            query = em.createNamedQuery("getThresholdParameters");
            query.setParameter(1, Integer.parseInt(circleId));

            List<Object[]> resultList = new ArrayList();
            resultList  = query.getResultList();

Here I get result as List<Object[]>, thus I have to type convert all the parameters of the row to their respective types which is cumbersome.

In JPA 2.0 there is TypedQuery which return an entity object of type one specifies.

But as I am using JPA 1 I can't use it.

How to get result as Entity object of type I want??

EDIT: QUERY

@Entity
@Table(name="GMA_THRESHOLD_PARAMETERS")
@NamedQuery(

        name = "getThresholdParameters",

        query = "select gmaTh.minNumberOc, gmaTh.minDurationOc, gmaTh.maxNumberIc, gmaTh.maxDurationIc, gmaTh.maxNumberCellId,"
                + "gmaTh.distinctBnumberRatio, gmaTh.minPercentDistinctBnumber from GmaThresholdParameter gmaTh " 
                + "where gmaTh.id.circleId=?1 AND gmaTh.id.tspId=?2 AND gmaTh.id.flag=?3 "
        )

回答1:

Your query selects many fields. Such a query always returns a list of Object arrays. If you want a list containing instances of your GmaThresholdParameter entity, then the query should be

select gmaTh from GmaThresholdParameter gmaTh 
where gmaTh.id.circleId=?1 AND gmaTh.id.tspId=?2 AND gmaTh.id.flag=?3

The code to get the list of entities would then be

List<GmaThresholdParameter> resultList = query.getResultList();

You'll get a type safety warning from the compiler, that you can ignore.

回答2:

I can't respond to this as a comment so I'll just go ahead and make it an answer.

List<Object[]> resultList = new ArrayList(); // CREATE an empty ArrayList object
resultList  = query.getResultList(); // getResultList ALSO returns its own ArrayList object

And since you assign the list that getResultList() returns to the same variable as you used for your own empty ArrayList, your application loses any connection to your own empty ArrayList and Java will collect it as garbage. Essentially you created it for absolutely no purpose.

what JB Nizet posted is enough.

List<GmaThresholdParameter> resultList = query.getResultList();

回答3:

I have done something similar since I was using JPA 1 at that time:

    final Collection<YourType> typedResult = new ArrayList<YourType> 
    for(final Object result : query.getResultList()) 
    { 
         typedResult.add((YourType) result); 
    }  
    return typedResult;

回答4:

 List<GmaThresholdParamerter> result= query.getResultList();
   for( GmaThresholdParamerter res : result)
   {
     System.out.println("" +res.getMinNumberOc());
     System.out.println("" +res.getMinDurationOc());
  }

来源：https://stackoverflow.com/questions/20901282/jpa-query-getresultlist

标签

java

java-ee

jpa

persistence