Why is hibernate deleting before saveOrUpdate ()?

Question

I have am: n relation between Column and Element. The entity that owns the relationship is Column. But when I'm saving a map of Columns, the following scenario occurs:

1) In the first iteration, Hibernate:

1.1) saves the first Column element

1.2) inserts the two elements in the column_element table

follows console:

Hibernate: select nextval ('hibernate_sequence')
Hibernate: insert into coluna (COLUNA_ALIAS_OPERACAO, COLUNA_CLAUSULA, COLUNA_DATA_DOIS, COLUNA_DATA_UM, COLUNA_EXIBE_FILTRO, COLUNA_EXIBE_NO_RELATORIO, COLUNA_EXIBE_TOTALIZADOR, COLUNA_INDEX, COLUNA_LABEL, COLUNA_NOME, COLUNA_OPERACAO, COLUNA_OPERACAO_REFERNCIANDO_ALIAS, RELATORIO_ID, COLUNA_TEMPO_DOIS, COLUNA_TEMPO_UM, COLUNA_TIPO_CLAUSULA_TEXTO, COLUNA_TIPO_EXIBICAO, COLUNA_TIPO_FILTRO, COLUNA_ID) values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
Hibernate: insert into coluna_elemento (COLUNA_ID, ELEMENTO_DOMINIO_ID) values (?, ?)
Hibernate: insert into coluna_elemento (COLUNA_ID, ELEMENTO_DOMINIO_ID) values (?, ?)

At this moment the table column_element of my database is like this:

coluna_id | elemento_id
988        860
988        861

So far everything is happening as expected.

2) In the second iteration, Hibernate:

2.1) saves the second column element

2.2) deletes from the column_element element the previously saved element

2.3) inserts the two elements in the column_element_element

As the output from the following console shows:

Hibernate: select nextval ('hibernate_sequence')
Hibernate: insert into coluna (COLUNA_ALIAS_OPERACAO, COLUNA_CLAUSULA, COLUNA_DATA_DOIS, COLUNA_DATA_UM, COLUNA_EXIBE_FILTRO, COLUNA_EXIBE_NO_RELATORIO, COLUNA_EXIBE_TOTALIZADOR, COLUNA_INDEX, COLUNA_LABEL, COLUNA_NOME, COLUNA_OPERACAO, COLUNA_OPERACAO_REFERNCIANDO_ALIAS, RELATORIO_ID, COLUNA_TEMPO_DOIS, COLUNA_TEMPO_UM, COLUNA_TIPO_CLAUSULA_TEXTO, COLUNA_TIPO_EXIBICAO, COLUNA_TIPO_FILTRO, COLUNA_ID) values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
Hibernate: delete from coluna_elemento where COLUNA_ID=?
Hibernate: insert into coluna_elemento (COLUNA_ID, ELEMENTO_DOMINIO_ID) values (?, ?)
Hibernate: insert into coluna_elemento (COLUNA_ID, ELEMENTO_DOMINIO_ID) values (?, ?)

And then, the column_element element in the database looks like this:

coluna_id  |  elemento_id
   989           860
   989           861

When what I expected was the following:

coluna_id | elemento_id
   988          860
   988          861
   989          860
   989          861

What am I doing wrong?

The code where I save the column map is as follows:

private void salvaColunas() {
   for (Map.Entry<Integer, Coluna> entry : mapaColunas.entrySet()){
       Coluna coluna = entry.getValue();
       coluna.setRelatorio(relatorio);
       colunaDao.saveOrUpdate(coluna);
   }
}

The saveOrUpdate method of my Dao class is as follows:

public void saveOrUpdate(T obj) {
   Session session;
   Transaction tx = null; 
   try {
       session = HibernateUtil.getSessionFactory().getCurrentSession();
   }catch (HibernateException ex) {
       session = HibernateUtil.getSessionFactory().openSession();
   }
   try{
       tx = session.beginTransaction();
       session.saveOrUpdate(obj);
       tx.commit();
   } catch (RuntimeException e) {
       e.printStackTrace();
   } finally {
      if(session.isOpen()) {
          session.close();
      }
  }
}

The mapping in the Column class (already with equals and hashCode methods implemented) looks like this:

@ManyToMany(fetch= FetchType.LAZY, cascade= {CascadeType.PERSIST,cadeType.REFRESH, CascadeType.MERGE})
@JoinTable(name="coluna_elemento",  joinColumns={
@JoinColumn(name="COLUNA_ID", nullable=false, updatable=false )},inverseJoinColumns = {@JoinColumn(name = "ELEMENTO_DOMINIO_ID", nullable=false, updatable = false)  })
private Set<ElementoDominio> elementosDoDominio;

@Override
public int hashCode() {
   final int prime = 31;
   int result = 1;
   result = prime * result + ((id == null) ? 0 : id.hashCode());
   result = prime * result + ((label == null) ? 0 : label.hashCode());
   result = prime * result + ((nome == null) ? 0 : nome.hashCode());
   return result;
 }

@Override
public boolean equals(Object obj) {
   if (this == obj)
    return true;
   if (obj == null)
    return false;
   if (getClass() != obj.getClass())
    return false;
  Coluna other = (Coluna) obj;
  if (id == null) {
    if (other.id != null)
        return false;
  } else if (!id.equals(other.id))
    return false;
  if (label == null) {
    if (other.label != null)
        return false;
  } else if (!label.equals(other.label))
    return false;
  if (nome == null) {
    if (other.nome != null)
        return false;
  } else if (!nome.equals(other.nome))
    return false;
  return true;
}

And my Element class (which also has the equals and hashCode methods implemented) looks like this:

@ManyToMany(fetch = FetchType.LAZY, mappedBy = "elementosDoDominio")
private Set<Coluna> colunas;

@Override
public int hashCode() {
   final int prime = 31;
   int result = 1;
   result = prime * result + ((id == null) ? 0 : id.hashCode());
   result = prime * result + ((label == null) ? 0 : label.hashCode());
   return result;
}

@Override
public boolean equals(Object obj) {
   if (this == obj)
    return true;
   if (obj == null)
    return false;
   if (getClass() != obj.getClass())
    return false;
   ElementoDominio other = (ElementoDominio) obj;
   if (id == null) {
    if (other.id != null)
        return false;
   } else if (!id.equals(other.id))
    return false;
   if (label == null) {
    if (other.label != null)
        return false;
   } else if (!label.equals(other.label))
    return false;
   return true;
}

Both the Column and Element classes have more attributes, including the id that is generated by Hibernate. All with getters and setters.

Answer 1

It'is highly recommended to avoid the use of @ManyToMany clause,Can you try to change it by implementing association table explicitly as entity and use @manyToOne instead :

ElementoDominio class

@OneToMany(mappedBy="element")
private Set<ElementoDominio> elementosDoDominio;

Coluna class

@OneToMany(mappedBy="colunas")
private Set<Coluna> colunas;

ElementoColuna [New entity]

    @ManyToOne
    @JoinColumn(name="element_id")
    private ElementoDominio element

    @ManyToOne
    @JoinColumn(name="colunas_ID")
    private Coluna colunas