JPA how to group by a collection property - jpa

Question

Is there a way to group by a collection property? For example,
public class Merchandise {
id,
name
}
public class Attribute {
id,
name,
value,
#ManyToOne
MerchandiseCost merchandiseCost;
}
public class MerchandiseCost {
Merchandise merchandise,
List<Attribute> attributes,
BigDecimal cost,
}
Search MerchandiseCost group by merchandise and attributes.
select merchandise, attributes, sum(cost) from MerchandiseCost group by merchandise, attributes.
Will this be going to work?
EDIT:
If not, how to build a query to get results as following using CriteriaQuery API:
Merchandise Attributes SUM(COST)
-----------------------------------------------------------
Cloth size:L, color:RED 10000
Cloth size:M, color:WHITE 20000
Computer Memory:4G 80000
Computer Memory:16G 90000

Answer 1

You can not group by a collection and cannot select multi-valued field in the Select clause.
Merchandise.class
#Data
#Embeddable
#NoArgsConstructor
#EqualsAndHashCode
public class Merchandise {
private String name;
}
Attribute.class
#Data
#Embeddable
#EqualsAndHashCode
public class Attribute {
private int id;
private String name;
private String value;
private MerchandiseCost merchandiseCost;
#ManyToOne
public MerchandiseCost getMerchandiseCost() {
return merchandiseCost;
}
}
MerchandiseCost.class
#Data
#Entity
#EqualsAndHashCode
public class MerchandiseCost extends ABaseEntity {
private Merchandise merchandise;
private List<Attribute> attributes;
private BigDecimal cost;
#Embedded
public Merchandise getMerchandise() {
return merchandise;
}
public void setMerchandise(Merchandise merchandise) {
this.merchandise = merchandise;
}
#ElementCollection
#CollectionTable(name = "MERCHANDISE_ATTRIBUTE", joinColumns = #JoinColumn(name = "MERCHANDISE_ID"))
public List<Attribute> getAttributes() {
return attributes;
}
}
MerchandiseResult.class
#Data
#NoArgsConstructor
#AllArgsConstructor
#EqualsAndHashCode
public class MerchandiseResult {
private Merchandise merchandise;
private Attribute attribute;
private BigDecimal cost;
}
MerchandiseDao.class
#Stateless
public class MerchandiseDao {
#PersistenceContext(name = "tngo")
private EntityManager entityManager;
public void readCost(){
Query query = entityManager.createQuery("select NEW tngo.cert.training.model.MerchandiseResult(mc.merchandise, att, sum(mc.cost)) from MerchandiseCost mc join mc.attributes att group by mc.merchandise, att");
query.getResultList();
}
}