从JPA Query.getResultList（）映射到自定义的TO [英] mapping list from JPA Query.getResultList() to a customized TO

问题描述

我有一个表格，里面有四列id，名称，颜色和形状。表中的

条目为：

  1，苹果，红色，圆形
 2，香蕉，黄色，长形
 3，番茄红色圆形
 4，橙色，橙色，圆形
  

现在我创建了一个实体类Fruit映射到上表。

  @Entity 
 @Table（name =fruit）
 public class Fruit实现Serializable {
 
 @Id 
 @Column（name =ID）
字符串ID; 
 
 @Column（name =NAME）
字符串名称; 
 
 @Column（name =COLOR）
字符串颜色; 
 
 @Column（name =SHAPE）
字符串形状; 
 
 // getters / setters去这里
} 
  

我的DAO类的代码是：

  String myQuery =从f中选择f.shape，f.name f。 shape =：shape; 
查询查询= this.em.createQuery（myQuery）; 
 query.setParameter（shape，round）; 
  

显而易见，运行上面的查询将返回3行。

我有一个简单的TO类FruitSearchTO

  class FruitSearchTO 
 {
字符串形状; 
字符串名称; 
 
 // getters / setters here 
} 
  

符合我查询返回的行。

但是在我的DAO中运行如下所示：

 列表与LT; FruitSearchTO> fruitList = new ArrayList< FruitSearchTO>（）; 
 fruitList = query.getResultList（）; 
  

抛出异常java.lang.ClassCastException：[Ljava.lang.Object;与FruitSearchTO不兼容]

我在哪里错了，这个解决方案是什么？

解决方案

您使用的HQL将返回 List< Object []> code>是位置0中 shape 的数组，而位置1中是 name 。

您可以使用 List< FruitSearchTO> /hibernate/core/4.0/javadocs/org/hibernate/transform/Transformers.html#aliasToBean%28java.lang.Class%29rel =nofollow> AliasToBeanResultTransformer ：

  List fruitList = s.createQuery（
select f.shape as shape，f.name （f.shape =：shape;）
 .setParameter（shape，paramShape）
 .setResultTransformer（Transformers.aliasToBean（FruitSearchTO.class））
 .list （）; 
 FruitSearchTOdto =（FruitSearchTO）fruitList .get（0）; 
  

或者，如果 FruitSearchTO 具有适当的构造函数：，你也可以通过选择新的FruitSearchTO（f.shape，f.name）来实现。

查看关于HQL的Hibernate Reference章节，特别是 15.6 选择子句一章。

I have a table fruit with four columns id, name, color, shape.

entries in the table would be:

1, apple, red, round
2, banana, yellow, long
3, tomato, red, round
4, orange, orange, round

Now I made an entity class Fruit mapped to above table.

@Entity
@Table(name="fruit")
public class Fruit implements Serializable {

@Id
@Column(name="ID")
String id;

@Column(name="NAME")
String name;

@Column(name="COLOR")
String color;

@Column(name="SHAPE")
String shape;

//getters/setters goes here
}

In my DAO class, the code is:

String myQuery = "Select f.shape, f.name from Fruit f where f.shape = :shape";
Query query = this.em.createQuery(myQuery);
query.setParameter("shape", "round");

As obvious, running above query will return 3 rows.

I have a simple TO class FruitSearchTO

class FruitSearchTO
{
  String shape;
  String name;

  //getters/setters here
}

This TO complies with the rows returned by my query.

But in my DAO running something like:

List<FruitSearchTO> fruitList = new ArrayList<FruitSearchTO>();  
fruitList = query.getResultList();

is throwing exception java.lang.ClassCastException: [Ljava.lang.Object; incompatible with FruitSearchTO]

Where am I going wrong and what is the solution to this ?

解决方案

The HQL you're using will return a List<Object[]>, each element of the List being an array with shape in position 0 and name in position 1.

You can make the HQL return a List<FruitSearchTO> using an AliasToBeanResultTransformer:

List fruitList = s.createQuery(
  "select f.shape as shape, f.name as name from Fruit f where f.shape = :shape;")
  .setParameter("shape", paramShape)
  .setResultTransformer( Transformers.aliasToBean(FruitSearchTO.class))
  .list();
FruitSearchTOdto = (FruitSearchTO) fruitList .get(0);

Alternatively, if FruitSearchTO has an appropriate constructor:, you can also achieve this with select new FruitSearchTO(f.shape, f.name).

Take a look at the Hibernate Reference chapter on HQL, particularly 15.6 The select clause chapter.

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