Playframework How to transform query.ResultList to VO - jpa

Question

The version of Playframework is 1.2.x,and I want to transform the query.ResultList to VO.
I created a Part entity bean as below:
#Entity
#Table(name="evaluation_part")
public class Part extends Model {
public String name;
public String collegeName;
public int peopleNum;
}
The data:
id name collegeName peopleNum
1 Jsj1 JJJJ 32
2 Jsj2 JJJJ 23
3 Jsj3 JJJJ 32
4 Tjb1 TTTT 11
5 Tjb2 TTTT 14
6 Tjb3 TTTT 16
My value object class:
public class PartVO {
public String collegeName;
public int peopleNum;
}
And I want to use the native query to get the result:
String sql="select collegeName,SUM(peopleNum) as peopleNum from evaluation_part group by collegeName";
The query result is:
collegeName peopleNum
TTTT 41
JJJJ 87
I tried：
String sql="select collegeName,SUM(peopleNum) as peopleNum from evaluation_part group by collegeName";
Query query =JPA.em().createNativeQuery(sql);
List<PartVO> partVOs = query.getResultList();
for(int i=0;i<partVOs.size();i++) {
System.out.println(partVOs.get(i).collegeName);
}
Following error is what i am getting
ClassCastException occured : [Ljava.lang.Object; cannot be cast to valueobject.PartVO

Answer 1

You don't have to user raw sql to do that. With hql you can use the new operator to create your VO (see http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/queryhql.html#queryhql-select)
You have to define a two arg constructor in your partVO class, then you can do
select new package.PartVO(collegeName, SUM(peopleNum)) from Part group by collegeName

Answer 2

Solution 1:Only use 'select new Part()'(constructor defined in the Part class) in the HQL that u can convert object to Part.Hibernate use reflection to automatically inject all the fields u need.
Solution 2:Here the returned type of result must be Object[],so that u can got every field of the record fetched from database by the index of array;
The difference between solution1 and solution2:the previous use constructor in the query and the later transform a record into Object[].
In your case,ignore the complex relationship between entities,solutions above will make work.
Referenced Code here:
package controllers;
import play.*;
import play.db.jpa.JPA;
import play.mvc.*;
import java.util.*;
import models.*;
/**
* This demo is intended for fetching data from MYSQL.
* #author dhl#oopsplay.org
*/
public class Application extends Controller {
public static void index() {
render();
}
/**
* Prepare some data to test.
*/
public static void addPart() {
//Add a part record to database.
Part newPart=new Part("software","zjut",8).save();
if(newPart.isPersistent()){
renderText("Add successfully,there are %s records in the \'evaluation_part\' table.For convenience,please click the back button in the browser to go back previous page.",Part.count());
}
}
/**
* Fetch part entities from database;
*/
public static void fetchPart() {
//-------------------Solution 1-------------------
//[Pay attention]:Only use 'select new Part()'(constructor defined in the Part class) in the query that u can convert object to Part.
//Hibernate use reflection to automatically inject all the fields u need.
List<Part> parts1=JPA.em().createQuery("select new Part(name,collegeName,peopleNum) from Part").getResultList();
//For convenience, i output the detail in the console, focus on the change there.
Logger.info("The name of first record is :%s", parts1.get(0).name);
//-------------------Solution 2-------------------
//[Pay attention]:Here the returned type of result must be Object[],so that u can got every field of the record fetched from database;
List<Object[]> parts2=JPA.em().createNativeQuery("select name,collegeName,peopleNum from evaluation_part").getResultList();
Logger.info("The name of first record is :%s", parts2.get(0)[0]);
for(int i=0;i<parts2.size();i++){
//The difference between solution1 and solution2:the previous use constructor in the query and the later transform a record into Object[].
Logger.info("Name from parts1 is: %s", parts1.get(i).name);
Logger.info("Name from parts2 is: %s", parts2.get(i)[0]);
}
renderText("There are %s record in the \'evaluation_part\' table",parts2.size());
}
}

Answer 3

You can use the version of createNativeQuery(...) method that also accepts as argument the Class of the result instance(s):
http://docs.oracle.com/javaee/6/api/javax/persistence/EntityManager.html#createNativeQuery(java.lang.String, java.lang.Class).
However make sure this actually works, as Play Framework doesn't implement all the features of JPA in it's implementation of the API.