没有基础表的JPA实体

Question

我想创建一个可以映射到使用JPA原生查询从数据库提取的结果的类。有没有办法将没有基础表的实体映射到结果？我提到了这个允许它Hibernate的链接。这可以用JPA来代替吗？

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

JPA2.1规范定义了将本机查询结果返回给非实体类的方法

您应该签出标题3.10.16.2返回非托管实例，尤其是

3.10.16.2.2施工结果

到构造函数的映射是使用SqlResultMapping注释的ConstructorResult注释元素指定的。ConstructorResult注释的targetClass元素指定其构造函数对应于指定列的类。必须使用ConstructorResult注释的columns元素，按照与构造函数的参数列表相同的顺序指定与预期构造函数的参数对应的所有列。作为构造函数结果返回的任何实体都将处于新状态或分离状态，具体取决于是否为构造的对象检索主键。

实例

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)})
        })