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Does deleting a relationsip remove the dependant object from the database? [message #654540]

Wed, 16 February 2011 04:16

Tony Dietrich
Messages: 8
Registered: February 2011
Location: UK

Junior Member

If I have the classic Person entity object, with associated TelephoneNumber objects in a OneToMany relationship, does loading the relationship collection of the parent Person object, then deleting one of the TelephoneNumber objects from this collection and merging the parent object back to the database trigger the deletion of that TelephoneNumber from the database, assuming I have orphanRemoval=true ?

class Person{
....

@OneToMany(mappedBy="telephone", cascade=CascadeType.ALL, orphanRemoval=true)
private Collection<TelephoneNumber> telephoneNumberCollection;

...

}

*************************

Person p=personFacade.getPersonForID(id);
List<TelephoneNumber> lst=p.getTelephoneNumberCollection();
For(TelephoneNumber t:lst){
if(t.getName().equals("Home") lst.remove(t);
}
personFacade.merge(p);

Will this pseudocode result in the removal from the database of the 'Home' telephone number?

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Re: Does deleting a relationsip remove the dependant object from the database? [message #654558 is a reply to message #654540]

Wed, 16 February 2011 04:27

Tom Eugelink
Messages: 801
Registered: July 2009

Senior Member

You only delete something if you execute the remove method of an entity manager. It may very well be possible that this cascades the delete to other entities (this is what the CascadeType is for).

Your code only removes an object from a collection, not from the database.

Tom

On 16-2-2011 10:16, Tony Dietrich wrote:
> If I have the classic Person entity object, with associated TelephoneNumber objects in a OneToMany relationship, does loading the relationship collection of the parent Person object, then deleting one of the TelephoneNumber objects from this collection and merging the parent object back to the database trigger the deletion of that TelephoneNumber from the database, assuming I have orphanRemoval=true ?
>
> class Person{
> ...
>
> @OneToMany(mappedBy="telephone", cascade=CascadeType.ALL, orphanRemoval=true)
> private Collection<TelephoneNumber> telephoneNumberCollection;
>
> ..
>
> }
>
> *************************
>
> Person p=personFacade.getPersonForID(id);
> List<TelephoneNumber> lst=p.getTelephoneNumberCollection();
> For(TelephoneNumber t:lst){
> if(t.getName().equals("Home") lst.remove(t);
> }
> personFacade.merge(p);
>
>
>
> Will this pseudocode result in the removal from the database of the 'Home' telephone number?

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Re: Does deleting a relationsip remove the dependant object from the database? [message #654561 is a reply to message #654558]

Wed, 16 February 2011 05:20

Tony Dietrich
Messages: 8
Registered: February 2011
Location: UK

Junior Member

Would it have any effect if I included

Person p=personFacade.getPersonForID(id);
 List<TelephoneNumber> lst=p.getTelephoneNumberCollection();
 For(TelephoneNumber t:lst){
 if(t.getName().equals("Home") lst.remove(t);
 }

p.setTelephoneNumberCollection(lst);

 personFacade.merge(p);

I'm looking at
http://en.wikibooks.org/wiki/Java_Persistence/Relationships# Orphan_Removal_.28JPA_2.0.29

which implies that this deletion is specified by JPA 2.0 in circumstances where the dependant object is no longer referenced by the parent object.
Would de-referencing require that the reference is removed on both ends of the relationship though?

If I adopt the alternative approach (specifically deleting the dependant object using EntityManager.remove), is the parent collection automatically updated or do I have to force a refresh?

[Updated on: Wed, 16 February 2011 05:23]

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Re: Does deleting a relationsip remove the dependant object from the database? [message #654615 is a reply to message #654561]

Wed, 16 February 2011 08:48

Tom Eugelink
Messages: 801
Registered: July 2009

Senior Member

Nope. Something like lEntityManager.remove(t); would help.

On 16-2-2011 11:20, Tony Dietrich wrote:
> Would it have any effect if I included
>
>
> Person p=personFacade.getPersonForID(id);
> List<TelephoneNumber> lst=p.getTelephoneNumberCollection();
> For(TelephoneNumber t:lst){
> if(t.getName().equals("Home") lst.remove(t);
> }
>
> p.setTelephoneNumberCollection(lst);
>
> personFacade.merge(p);
>
>
> I'm looking at http://en.wikibooks.org/wiki/Java_Persistence/Relationships# Orphan_Removal_.28JPA_2.0.29
>
> which implies that this deletion is specified by JPA 2.0 in circumstances where the dependant object is no longer referenced by the parent object.
> Would de-referencing require that the reference is removed on both ends of the relationship though?
>
>

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Re: Does deleting a relationsip remove the dependant object from the database? [message #654616 is a reply to message #654561]

Wed, 16 February 2011 08:49

Tom Eugelink
Messages: 801
Registered: July 2009

Senior Member

Or, if you do not intend to delete it but simple break the relationship, setting the owning side of the relation. Probably something like lst.setPerson(null);

On 16-2-2011 11:20, Tony Dietrich wrote:
> Would it have any effect if I included
>
>
> Person p=personFacade.getPersonForID(id);
> List<TelephoneNumber> lst=p.getTelephoneNumberCollection();
> For(TelephoneNumber t:lst){
> if(t.getName().equals("Home") lst.remove(t);
> }
>
> p.setTelephoneNumberCollection(lst);
>
> personFacade.merge(p);
>
>
> I'm looking at http://en.wikibooks.org/wiki/Java_Persistence/Relationships# Orphan_Removal_.28JPA_2.0.29
>
> which implies that this deletion is specified by JPA 2.0 in circumstances where the dependant object is no longer referenced by the parent object.
> Would de-referencing require that the reference is removed on both ends of the relationship though?
>
>

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Re: Does deleting a relationsip remove the dependant object from the database? [message #654617 is a reply to message #654616]

Wed, 16 February 2011 08:56

Tony Dietrich
Messages: 8
Registered: February 2011
Location: UK

Junior Member

Thanks for your input Tom Smile

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Re: Does deleting a relationsip remove the dependant object from the database? [message #654619 is a reply to message #654561]

Wed, 16 February 2011 09:00

Chris Delahunt
Messages: 862
Registered: July 2009

Senior Member

Hello Tony,

Yes, OrphanRemoval will result in PhoneNumbers being deleted from the database when they are no longer referenced from Person. The code in the first post should work, and there is no need to call p.setTelephoneNumberCollection(lst) as you are manipulating the collection already. EntityManager.remove(t) should not be needed - be sure that nothing else references t though, and especially not with a cascade persist/merge relationship, as this will leave your cache inconsistent with the database and potentially cause the object to be resurected later on.

What Tom mentioned is correct when OrphanRemoval or PrivateOwnership (native EclpseLink) is not used.

Best Regards,
Chris

[Updated on: Wed, 16 February 2011 09:03]

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Re: Does deleting a relationship remove the dependant object from the database? [message #654637 is a reply to message #654619]

Wed, 16 February 2011 09:36

Tony Dietrich
Messages: 8
Registered: February 2011
Location: UK

Junior Member

I hope so.

Running a test now, I'll let you know if it works.

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Re: Does deleting a relationsip remove the dependant object from the database? [message #654669 is a reply to message #654617]

Wed, 16 February 2011 10:57

Tom Eugelink
Messages: 801
Registered: July 2009

Senior Member

On 16-2-2011 14:56, Tony Dietrich wrote:
> Thanks for your input Tom :)

You're welcome. Just trying to give something back for such a great free(!) software library.

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