Hibernate one to many returning multipe duplicate objects

Question

I have a one to many relation entities Scenario is like this EmployeeGroupActivity has Many EmployeeActivity Hibernate Mapping is done as follows

@Entity
@Table(name = “employeegroupactivity”)
@DynamicUpdate
public class EmployeeGroupActivity{

    /**
     * 
     */
    private static final long serialVersionUID = -9114620718714111316L;
    private Integer     groupActivityId;            

    private Set<EmployeeActivity> employeeActivities;

    public EmployeeGroupActivity(){

    }

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "groupActivityId")
    public Integer getGroupActivityId() {
        return groupActivityId;
    }
    public void setGroupActivityId(Integer groupActivityId) {
        this.groupActivityId = groupActivityId;
    }

    @OneToMany(targetEntity = EmployeeActivity.class,mappedBy = "groupEmployeeActivity",fetch = FetchType.LAZY)
        public Set<EmployeeActivity> getEmployeeActivities() {
            return employeeActivities;
        }

        public void setEmployeeActivities(Set<EmployeeActivity> employeeActivities) {
            this.employeeActivities = employeeActivities;
        }
}

// EmployeeActivity
@Entity
@Table(name = "employeeactivity")
@DynamicUpdate
public class EmployeeActivity{
  private Integer empActivityId;
  String activityDescription;
  Date  activityDate;
  private Integer eventId;      
  private EmployeeGroupActivity groupEmployeeActivity; //This is mapped as ManyToOne
}

// Query Part
Criterion eventIdCriterion = Restrictions.eq(“EG.eventId", eventId);
                        Projection projection = Projections.projectionList()
                                .add(Projections.property(“EG.groupActivityId"),"groupActivityId")
                                .add(Projections.property("EMPACT.empActivityId”), "employeeActivities.empActivityId")
                                .add(Projections.property("EMPACT.activityDescription”), "employeeActivities.activityDescription")
                                .add(Projections.property("EMPACT.activityDate"), "employeeActivities.activityDate");


Criteria criteria = sessionObject.createCriteria(EmployeeGroupActivity.class,”EG")
                    .createAlias(“EG.employeeActivities", “EMPACT”)
                    .setProjection(projection)
                    .add(eventIdCriterion);

criteria
.setResultTransformer(new AliasToBeanNestedResultTransformer(
        GroupActivityResponse.class));

When I fetch EmployeeGroupActivity with a where clause I am expecting one EmployeeGroupActivity for an event which has many EmployeeActivity objects.

But I am getting result as Many EmployeeGroupActivity objects all with same groupActivityId but each object has one EmployeeActivity object in a set of EmployeeActivity.

This happens only when I use projections with hibernate criteria, If I don't use projections I will get one EmployeeGroupActivity object which has many EmployeeActivity objects.

I am using setResultTransformer for criteria and a library http://stackoverflow.com/questions/20331852/java-hibernate-transformer-aliastobeannestedresulttransformer posted by some in in SO

How to get Set of employee activities with projections ? I have many such requirement and every where I have to iterate the result and make one root object add all set items then return in response which takes lot of iterations.

Update : note that DISTINCT_ROOT_ENTITY didn't work

Answer 1

This is a known issue for Hibernate criteria. A work around to eliminate duplicates is to get the distinct id's matching your constraints by

criteria.setProjection(Projections.distinct(Projections.id()));
idList = criteria.list();

and then you can create another criteria to get details of the returned id's

criteria2.add(Restrictions.in("id", idList));
requiredList = cr.list();

Hope this works.