Hibernate: ordering a Set

Question

I have a class Person who has a set of Books. It is not meaningful in the particular case to have an ordered or sorted collection.

Say now that I have a search page

Answer 1

Like said Markos Fragkakis

unfortunately order-by in the mapping (or @OrderBy) takes precedence, which makes the ordering set by the Criteria useless.

But you must set @Order if you want to have the Set ordered.

You can still use HQL instead ( tested on hibernate 3.3.2.GA ) who order firstly by the order in the hql query :

    @Entity
    @Table(name = "Person")
    public class Person  {

        @Id
        @Column(name = "ID_PERSON", unique = true, nullable = false, precision = 8, scale = 0)
        private Long id;

        @OneToMany(fetch = FetchType.LAZY, mappedBy = "person")
        @OrderBy
        private Set<Book> books = new HashSet<Book>(0);

        public Person() {
        }

        public Long getId() {
            return this.id;
        }

        public void setId(Long id) {
            this.id = id;
        }


      public Set<Book> getBooks() {
            return this.books;
        }

        public void setBooks(Set<Book> books) {
            this.books = books;
        }

    }

      /** 
       *  hql Version 
       *    
       *  Result in : 
       *  order by
       *      book1_.TITLE asc,
       *      book1_.ID_BOOK asc  
       **/

        @Override
        public Person getFullPerson(Long idPerson) {

            StringBuilder hqlQuery =  new StringBuilder();
            hqlQuery.append("from Person as p ");
            hqlQuery.append("left join fetch p.books as book ");
            hqlQuery.append("where p.id = :idPerson ");
            hqlQuery.append("order by book.title ");
            Query query = createQuery(hqlQuery.toString());
            query.setLong("idPerson", id);
            return uniqueResult(query);

        }




      /** 
       *  criteria  Version // not usable 
       *    
       *  Result in : 
       *  order by
       *      book1_.ID_BOOK asc,
       *      book1_.TITLE asc  
       **/

      @Override
    public Person getFullPersonCriteria(Long idPerson) {

        Criteria criteria = ...
        criteria.add(Restrictions.eq("id", idPerson));
        criteria.createAlias("books", "book", CriteriaSpecification.LEFT_JOIN);
        criteria.addOrder(Order.asc("book.title"));
            return criteria.uniqueResult();
      }

Answer 2

Hibernate supports mapping a collection as a SortedSet. In your mappings you basically just need to specify an order-by clause. Take a look at this chapter in the reference manual.

Answer 3

This is an in-memory sort that will take care of duplicates in the join table.

  @OneToMany
  @JoinTable(name = "person_book", joinColumns = @JoinColumn(name = "person_id"),
             inverseJoinColumns = @JoinColumn(name = "book_id"))
  @Sort(type = SortType.COMPARATOR, comparator = MyBookComparator.class)
  private SortedSet<BookEntity> books;

Answer 4

not sure if i got the question right but if you just want an ordererd version of your list you can just sort it with the java.util.Collections class and a Comparator. Maybe you want to make a transient Method on your pojo like this:

@Transient
public List<Book> getBooksASC()
{
    Collections.sort(this.books, new BookSorter.TitelASCSorter());
    return this.books;
}

Just write a Class which implements Comparator.