JPA-在非实体类中连接两个表

Question

@Entity
class PersonA{
     String sample_field;
}

@Entity
class Person{
     String id;
     String name;

}

class PersonC
{
   Strind id;
   String address;
}

@SqlResultSetMapping(name="PersonC", 
classes = {
   @ConstructorResult(targetClass = PersonC.class, 
    columns = {@ColumnResult(name="name")
              , @ColumnResult(name="address")
    )}

Answer 1

@sqlresultsetmapping可以放置在任何实体类中（不要注释POJO-这是行不通的）。在JPA版本2.1中添加了使用@constructorresult到POJO类的映射。与映射一起使用的POJO必须有正确的构造函数。

必须使用ConstructorResult注释的columns元素以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相对应的所有列。

请参考下面的查询用法示例，并据此制定您的情况。

@Entity
public class Address {
    @Id int id;  
    String street;
}


@SqlResultSetMapping(name="PersonDTOMapping",
    classes = {
     @ConstructorResult(targetClass = PersonDTO.class,
       columns = {@ColumnResult(name="name"), @ColumnResult(name="street")}
     )}
)
@Entity
public class Person {
    @Id int id;
    String name;
    Address address;  
}  

public class PersonDTO {
    String name;
    String street;
    public PersonDTO(String name, String street) {
        this.name = name;
        this.street = street;
    }
}

// usage
Query query = em.createNativeQuery(
    "SELECT p.name AS name, a.street AS street FROM Person p, Address a WHERE p.address_id=a.id",
    "PersonDTOMapping");
List<PersonDTO> result = query.getResultList();