2

Playframework的版本是1.2.x，我想把query.ResultList转换成VO。

我创建了一个 Part 实体 bean，如下所示：

@Entity
@Table(name="evaluation_part")
public class Part extends Model {

    public String name;  

    public String collegeName;

    public int peopleNum;
}

数据：

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

我的价值对象类：

public class PartVO {

    public String collegeName;

    public int peopleNum;

}

我想使用本机查询来获得结果：

String sql="select collegeName,SUM(peopleNum) as peopleNum from evaluation_part group by collegeName";

查询结果为：

      collegeName      peopleNum

        TTTT              41
        JJJJ              87

我试过了：</p> 

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);
}

以下错误是我得到的

ClassCastException occured : [Ljava.lang.Object; cannot be cast to valueobject.PartVO
4

3 回答 3

2

您不必使用原始 sql 来执行此操作。使用 hql，您可以使用 new 运算符创建您的 VO（请参阅http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/queryhql.html#queryhql-select）

你必须在你的 partVO 类中定义一个两个 arg 构造函数，然后你可以做

select new package.PartVO(collegeName, SUM(peopleNum)) from Part group by collegeName
于 2012-08-29T06:33:06.000 回答
0

您可以使用 createNativeQuery(...) 方法的版本，该方法也接受结果实例的 Class 作为参数：

http://docs.oracle.com/javaee/6/api/javax/persistence/EntityManager.html#createNativeQuery(java.lang.String , java.lang.Class)。

但是请确保这确实有效，因为 Play Framework 并未在其 API 实现中实现 JPA 的所有功能。

于 2012-08-29T06:39:59.207 回答
0

解决方案1：仅在HQL中使用'select new Part()'（在Part类中定义的构造函数），您可以将对象转换为Part。Hibernate使用反射自动注入您需要的所有字段。

解决方案2：这里返回的结果类型必须是Object[]，这样就可以通过数组的索引获取从数据库中取出的记录的每一个字段；

解决方案1和解决方案2的区别：前者在查询中使用构造函数，后者将记录转换为Object[]。

在您的情况下，忽略实体之间的复杂关系，上述解决方案将起作用。

此处引用代码：

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());
}

}

于 2012-08-30T11:31:24.957 回答