How to prevent duplicate results in Hibernate?

Question

When trying to search for multiple values of a relation, duplicate results are returned.

How can I avoid these duplicates?

We have a method on our service that builds the Criteria:

@Override
protected Criteria createCriteria(Map<String, Object> values) {
    Criteria criteria = super.createCriteria(values);
    if (criteria != null && values != null) {

        // other criteria restrictions

        Set<MDTErkenning> erkenningen = (Set<MDTErkenning>) values.get("erkenningen");
        if (erkenningen != null && !erkenningen.isEmpty()) {
            criteria.createAlias("erkenningen", "erkenningen");
            criteria.add(Restrictions.in("erkenningen." + CollectionPropertyNames.COLLECTION_ELEMENTS, erkenningen));
        }

    }
    return criteria;
}

which is used to get out paged results and do a count:

@Override
public List<T> findByCriteria(Map<String, Object> values, int offset, int amount) {
    Criteria criteria = createCriteria(values)
            .setFirstResult(offset)
            .setMaxResults(amount);
    return criteria.list();
}

@Override
public Long getCount(Map<String, Object> values) {
    Criteria criteria = createCriteria(values).setProjection(Projections.rowCount());
    return (Long) criteria.uniqueResult();
}

Main entity

@Entity
@Table(name = "mdt")
public class MultiDisciplinairTeam {

    @Id
    @Column(name = "mdt_uuid")
    private String id;

    // other mappings

    @Column(name = "erkenning")
    @Cascade(org.hibernate.annotations.CascadeType.ALL)
    @ElementCollection(fetch = FetchType.EAGER)
    @Enumerated(EnumType.STRING)
    @JoinTable(name = "mdt_erkenning", joinColumns = {@JoinColumn(name = PK_NAME)})
    @Fetch(FetchMode.SELECT)
    private Set<MDTErkenning> erkenningen;

    // getters & setters 

}

Enum instead of entity

public enum MDTErkenning {
    ZORG("Zorg"),
    IMB("IMB"),
    PAB("PAB"),
    ROLSTOELEN("Rolstoelen");

    private String beschrijving;

    private MDTErkenning(String beschrijving) {
        this.beschrijving = beschrijving;
    }

    public String getBeschrijving() {
        return this.beschrijving;
    }
}

The join table mdt_erkenning with some data:

------------------------
| mdt_uuid | erkenning |
------------------------
| <id 1>   | ZORG      |
| <id 1>   | PAB       |
| <id 2>   | ZORG      |
| <id 2>   | IMB       |
------------------------

So if I query for eg. ZORG and PAB I get 3 instances of my entity: 2 with <id 1> and 1 with <id 2>.

I thought of putting the result list in a Set to eliminate the duplicates but then the pagination isn't correct anymore.

What should I do?

Answer 1

Try adding setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY) for removing duplicate entries and setProjection(Projections.distinct(Projections.property("id"))) for getting correct row count while creating criteria object.

Answer 2

Try to use this projection:

.setProjection(Projections.countDistinct("id"))

For your example:

@Override
public Long getCount(Map<String, Object> values) {
    Criteria criteria = createCriteria(values).setProjection(Projections.countDistinct("id"));
    return (Long) criteria.uniqueResult();
}

I am using Hibernate 4.3.6.Final.

Answer 3

I know it is an old thread but in cases, if someone is still having this problem, this Worked for me. More details here

 public List<User> getUserByUsername (String username)  
    {  
        Session session = sessionFactory.getCurrentSession();  
        return session.createCriteria(User.class)  
          .add(Restrictions.eq("username", username))  
          .setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY)  
          .list();  
    }