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Re: [eclipselink-users] ManyToMany did not persist in both directions
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In JPA, and Java object modeling in general, you should always set both sides
of a bi-directional relationship. Otherwise one side will be out of synch.
If you set both sides, it should work. A ManyToMany always only writes from
one side, the mappedBy side is basically read-only (otherwise you end up
with double the amount of rows).
See,
http://en.wikibooks.org/wiki/Java_Persistence/Relationships#Object_corruption.2C_one_side_of_the_relationship_is_not_updated_after_updating_the_other_side
farisola wrote:
>
> Using annotation @ManyToMany did not persist in both directions
>
> I have to n:m related tables, LEHRER and SCHUELER
>
> That results in 3 database tables:
>
> 1. LEHERER
> 2. SCHUELER
> 3. LEHERER_SCHUELER
>
> At the end you can find the two corresponding entity classes
> and the two test cases.
>
> Both entites contain the neccessary @ManyToMany annotations, see below.
> The entity LEHERER contains the @JoinTable annotation, the entity SCHUELER
> not.
>
> The problem:
>>>>
> If I persist a new LEHRER entity that contains some SCHUELER,
> then all three tables will have the corresponding entries.
>
> But if I persist a new SCHUELER entity that contains some LEHRER ,
> then ONLY the tables SCHUELER and LEHRER will have the corresponding
> entries,
> but the table LEHERER_SCHUELER will be ignored.
> <<<
>
> I think the persistence should work in both directions independent of the
> place,
> where the @JoinTable annotation is placed.
>
> All is running on a Oracle 10g Database.
>
> Did someone have an idea, what is wrong?
>
> //
> +-----------------------------------------------------------------------+
> @Entity
> @Table(name="LEHRER")
> public class Lehrer extends ZAdminEntity implements Serializable {
> private static final long serialVersionUID = 1L;
> private long pk;
> private String lehrername;
> private List<Schueler> schuelers;
>
> public Lehrer() { }
>
> @Id
> @SequenceGenerator(name="LEHRER_PK_GENERATOR",
> sequenceName="SEQ_LEHRER")
> @GeneratedValue(strategy=GenerationType.SEQUENCE,
> generator="LEHRER_PK_GENERATOR")
> @Column(unique=true, nullable=false, precision=22)
> public long getPk() {
> return this.pk;
> }
>
> public void setPk(long pk) {
> this.pk = pk;
> }
>
> @Column(nullable=false)
> public String getLehrername() {
> return this.lehrername;
> }
>
> public void setLehrername(String lehrername) {
> this.lehrername = lehrername;
> }
>
> //bi-directional many-to-many association to Schueler
> @ManyToMany(cascade={CascadeType.ALL}, fetch=FetchType.EAGER)
> @JoinTable(
> name="LEHRER_SCHUELER"
> , joinColumns={@JoinColumn(name="LEHRER_PK", nullable=false)}
> , inverseJoinColumns={@JoinColumn(name="SCHUELER_PK",
> nullable=false)}
> )
> public List<Schueler> getSchuelers() {
> return this.schuelers;
> }
>
> public void setSchuelers(List<Schueler> schuelers) {
> this.schuelers = schuelers;
> }
> }
>
> //
> +-----------------------------------------------------------------------+
> @Entity
> @Table(name="SCHUELER")
> public class Schueler extends ZAdminEntity implements Serializable {
> private static final long serialVersionUID = 1L;
> private long pk;
> private String schuelername;
> private List<Lehrer> lehrers;
>
> public Schueler() {}
>
> @Id
> @SequenceGenerator(name="SCHUELER_PK_GENERATOR",
> sequenceName="SEQ_SCHUELER")
> @GeneratedValue(strategy=GenerationType.SEQUENCE,
> generator="SCHUELER_PK_GENERATOR")
> @Column(unique=true, nullable=false, precision=22)
> public long getPk() {
> return this.pk;
> }
>
> public void setPk(long pk) {
> this.pk = pk;
> }
>
> @Column(nullable=false)
> public String getSchuelername() {
> return this.schuelername;
> }
>
> public void setSchuelername(String schuelername) {
> this.schuelername = schuelername;
> }
>
> //bi-directional many-to-many association to Lehrer
> @ManyToMany(mappedBy="schuelers", cascade={CascadeType.ALL},
> fetch=FetchType.EAGER)
> public List<Lehrer> getLehrers() {
> return this.lehrers;
> }
>
> public void setLehrers(List<Lehrer> lehrers) {
> this.lehrers = lehrers;
> }
>
> }
> //
> +-----------------------------------------------------------------------+
> @Test
> /**
> * Is working!
> */
> public void lehrerschueler() {
> EntityManagerFactory emf = getEMF();
> EntityManager em = emf.createEntityManager();
> Lehrer lehrer = this.getNewLehrer();
> Schueler schueler = this.getNewSchueler();
> ArrayList <Schueler> list = new ArrayList <Schueler> ();
> list.add(schueler);
> lehrer.setSchuelers(list);
> em.getTransaction().begin();
> try {
> // persist the lehrer
> em.persist(lehrer);
> em.getTransaction().commit();
> } catch (Exception e) {
> e.printStackTrace();
> Assert.fail(e.getMessage());
> }
> }
> //
> +-----------------------------------------------------------------------+
>
> @Test
> /**
> * IS NOT working!
> */
> public void schuelerlehrer() {
> EntityManagerFactory emf = getEMF();
> EntityManager em = emf.createEntityManager();
> Schueler schueler = this.getNewSchueler();
> Lehrer lehrer = this.getNewLehrer();
> ArrayList <Lehrer> list = new ArrayList <Lehrer> ();
> list.add(lehrer);
> schueler.setLehrers(list);
> em.getTransaction().begin();
> try {
> // persist the schueler
> em.persist(schueler);
> em.getTransaction().commit();
> } catch (Exception e) {
> e.printStackTrace();
> Assert.fail(e.getMessage());
> }
> }
> //
> +-----------------------------------------------------------------------+
>
> greetings Farisola
>
>
>
-----
http://wiki.eclipse.org/User:James.sutherland.oracle.com James Sutherland
http://www.eclipse.org/eclipselink/
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