JPA如何按集合属性分组

@Entity
@Table(name = "orders")
public class Order {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ManyToOne
    @JoinColumn(name = "customer_id")
    private Customer customer;

    // 其他属性...

    // getter和setter方法...
}

@Entity
@Table(name = "customers")
public class Customer {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    // 其他属性...

    // getter和setter方法...
}

// 在使用JPA进行查询时，可以按集合属性customer进行分组
String jpql = "SELECT o.customer, COUNT(o) FROM Order o GROUP BY o.customer";
TypedQuery<Object[]> query = entityManager.createQuery(jpql, Object[].class);
List<Object[]> results = query.getResultList();

// 遍历查询结果
for (Object[] result : results) {
    Customer customer = (Customer) result[0];
    Long count = (Long) result[1];
    // 处理每个分组的结果...
}