Adding a Projection to a List in Hibernate

Question

I have a @Entity called Order in this I have a field or a member variable called orderEmails as show below.

@Entity
@Table(name = \"order\")
public class Order {         


        

Answer 1

it's not possible like you expect. Hibernate has to group the records on the root entity which it only does for complete entities.

• you could load the complete entity eager fetching the emails and transform it in memory later.
• you fetch the root entity records duplicated for each email address and group them together in memory

Update:

List results = session.createCriteria(Order.class)
    .joinAlias("orderEmails", "email")
    .setProjection(Projections.projectionList()
        .add(Projections.property("id").as("id"))
        .add(Projections.property("email.EmailAddress").as("email")))
    .list();

Map> groups = new Hashmap>();
for (Object[] items : results)
{
    if (groups.containsKey((long)items[0]))
        groups.get((long)items[0]).add((String)items[1]);
    else
        groups.add((long)items[0], new List().add((String)items[1]));
}

return groups;

instead of the map one could also have dtos or something like that.