Question

Given a table, say:

orderId | typeId
----------------
1       | 1
2       | 1
3       | 2
4       | 5
5       | 1
6       | 2

And I have an Order object which has a Type object (Type has a Set of Orders in the other direction.

How would I go about retrieving the most popular Type of Order (in this case, type 1) using Hibernate’s Criteria API?

Answer 1

you might wanna look into Projections. You should be able to use Projections.groupProperty() on the “type” association, and add up the results.
check this SO question: Expressions in hibernate criteria

edit: tried it and the following seems to work fine:

Order:

@Entity
@Table(name="orders")
public class Order {
    @Id
    @GeneratedValue
    private long id;
    @ManyToOne
    private Type type;
}

Type:

@Entity
@Table(name="order_types")
public class Type {
    @Id
    @GeneratedValue
    private long id;
}

and the Criteria:

    Criteria c=sess.createCriteria(Order.class)
        .createCriteria("type")
        .setProjection(
                Projections.projectionList()
                .add(Projections.groupProperty("id"))
                .add(Projections.rowCount(),"rowcount")
        )
        .addOrder(org.hibernate.criterion.Order.desc("rowcount"));

    for (Object[] result:(List<Object[]>) c.list()){
        System.out.println("type id: " + result[0] + "\tcount: " + result[1]);
    }