JPA NamedQuery与聚合函数和分组依据一起使用

我的数据库表Foo上有几条记录,我需要聚合一个列来对其值求和。

@Entity
@Table(name = "FOO")
@NamedQueries({
@NamedQuery(name = "Foo.total", query = "SELECT f.id, sum(f.someInt) AS 
SOME_INT, f.parentId FROM Foo f where f.parentId = 'root' group by 
p.parentId"),
@NamedQuery(name = "Foo.findAll", query = "SELECT f from Foo f") })
public class Foo {

@Id
@Column(name = "ID", insertable = false, updatable = false)
private String id;

@Column(name = "PARENT_ID", insertable = false, updatable = false)
private String parentId;

@Column(name = "SOME_INT", insertable = false, updatable = false)
private Integer someInt;

public Foo() {
}

}

如果我在我的dao服务bean上调用这个:

entityManager.createNamedQuery("Foo.total", Foo.class).getResultList();

我发现这个错误:

Caused by: java.lang.IllegalArgumentException: Cannot create TypedQuery for query with more than one return using requested result type [Foo]

JPA似乎无法匹配对象Foo的返回值。如果是这样的话,我怎样才能让它发挥作用?