Re: [eclipselink-users] Unidirectional @OneToMany: is it possiblewith no

["Andrei Ilitchev" <andrei.ilitchev@xxxxxxxxxx>]

>It is not really so, card object could exist also without transaction (for example it can be created just for authentication purposes) and should be saved into separate DB table.

You can't have instances of the same class sometimes to be saved in one table and other times saved in another one in the same persistence unit - you have to have two different classes.

 

The only real disadvantage to embeddable I can see is inability to query - if that's important then make the relation bidirectional.

 

The foreign key in unidirectional OneToMany can't be non-nullable because (as opposed to Embedded ElementCollection member)

the target entity may be persisted (without source object existing).

 

em.getTransaction().begin();

Card card = new Card(...);

em.persist(card);

em.getTransaction().commit();

 

----- Original Message -----

From: Andrei Shakirin

To: EclipseLink User Discussions

Sent: Thursday, July 16, 2009 2:21 AM

Subject: RE: [eclipselink-users] Unidirectional @OneToMany: is it possiblewith not nullable foreign key?

Hi Andrei,

 

Thanks for the answer.

It is not really so, card object could exist also without transaction (for example it can be created just for authentication purposes) and should be saved into separate DB table.

Unfortunatelly embeddable is not a solution for me.

Interesting is the following: is it generally possible to organize unidirectional OneToMany relation if foreign key of "Many" entity is not nullable?

Is there any solution for it?

 

Regards,

Andrei.

---

From: eclipselink-users-bounces@xxxxxxxxxxx [mailto:eclipselink-users-bounces@xxxxxxxxxxx] On Behalf Of Andrei Ilitchev
Sent: Mittwoch, 15. Juli 2009 22:06
To: EclipseLink User Discussions
Subject: Re: [eclipselink-users] Unidirectional @OneToMany: is it possible with not nullable foreign key?

Card object can't exist without the corresponding Transaction object.

That means Card is not an independent object (Entity) but rather an owned object (Embeddable),

so OneToMany can't be used (the target must be an Entity).

 

I would define Card as Embeddable and use ElementCollection:

 

@Entity

@Table(name = "TRANS", schema="TEST")

public class TransactionType {

 

...

 

        @ElementCollection()

        @CollectionTable(name = "CARD", schema="TEST", @JoinColumn(name="TRANS_ID"))

        @AttributeOverrides({

            @AttributeOverride(name="a", column=@Column(name="URN"),

            @AttributeOverride(name="b", column=@Column(name="NUMBER"),

        })

        public java.util.Set<Card> getCards() {

                return cards;

        }

}

 

@Embeddable

public class CardUseTypeJAXB {

int a;

int b;

…

}

----- Original Message -----

From: Andrei Shakirin

To: eclipselink-users@xxxxxxxxxxx

Sent: Wednesday, July 15, 2009 1:49 PM

Subject: [eclipselink-users] Unidirectional @OneToMany: is it possible with not nullable foreign key?

Hello,

 

I have a problem to use unidirectional OneToMany in case if foreign key in second table is not nullable.

 

Sample:

Entities Transaction and Card are related as OneToMany:

 

@Entity

@Table(name = "TRANS", schema="TEST")

public class TransactionType {

 

...

 

        @OneToMany(cascade = CascadeType.ALL)

        @JoinColumn(name="TRANS_ID")

        public java.util.Set<Card> getCards() {

                return cards;

        }

}

 

@Entity

@Table(name = "CARD", schema="TEST")

public class CardUseTypeJAXB {

…

}

 

The problem is that TRANS_ID column in CARD table is not nullable.

Eclipse Link generates three SQL statements:

1) INSERT INTO TEST.TRANS (URN, NAME) VALUES (?, ?)

     bind => [28, 0000001Z]

2) INSERT INTO TEST.CARD (URN, NUMBER) VALUES (?, ?)

  bind => [6, 12345]

3) UPDATE TEST.CARD SET TRANS_ID ? WHERE (URN = ?)

 

The third statements throws exception if TRANS_ID column is not nullable: Column 'TRANS_ID' doesn't accept Null value. (with nullable column all works fine).

Unfortunately I cannot change the DB schema.

Is there any way to solve this problem?

 

Regards,

Andrei.

 

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