Question

我想创建一个可以映射到使用JPA本机查询从数据库中提取的结果的类。有没有办法将没有基础表的实体映射到结果？我提到this链接允许它进行休眠。这可以用JPA来完成吗？

这是我想要映射结果的类。

import java.math.BigDecimal;
import javax.persistence.Entity;
@Entity
public class OpUsage {  
    String username;    
    BigDecimal number_of_clicks;    
    String accordion;
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public BigDecimal getNumber_of_clicks() {
        return number_of_clicks;
    }
    public void setNumber_of_clicks(BigDecimal number_of_clicks) {
        this.number_of_clicks = number_of_clicks;
    }

    public String getAccordion() {
        return accordion;
    }

    public void setAccordion(String accordion) {
        this.accordion = accordion;
    }
}

Answer 1

JPA 2.1 specification定义了将结果从本机查询返回到非实体类的方法

您应该查看标题 3.10.16.2返回非托管实例，尤其是

3.10.16.2.2构造函数结果

使用 ConstructorResult 指定构造函数的映射 SqlResultSetMapping 注释的注释元素。该 ConstructorResult 注释的 targetClass 元素指定构造函数对应于指定列的类。所有与预期构造函数的参数对应的列必须是使用 ConstructorResult 的columns元素指定注释的顺序与参数列表的顺序相同构造函数。作为构造函数结果返回的任何实体都将在新的或分离的状态，取决于是否是主要的检索构造对象的密钥。

示例

Query q = em.createNativeQuery( "SELECT c.id, c.name, COUNT(o) as orderCount, AVG(o.price) AS avgOrder" + "FROM Customer c, Orders o " + "WHERE o.cid = c.id " + "GROUP BY c.id, c.name", "CustomerDetailsResult"); @SqlResultSetMapping(name = "CustomerDetailsResult", classes = { @ConstructorResult(targetClass = com.acme.CustomerDetails.class, columns = { @ColumnResult(name = "id"), @ColumnResult(name = "name"), @ColumnResult(name = "orderCount"), @ColumnResult(name = "avgOrder", type = Double.class)}) })

没有基础表的JPA实体

1 个答案: