EJB CMP 2.0 and Referential Integrity. 2004-11-19 - By Markus Fuchs
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Vikram,
Please excuse my late reply. AFAIK, there's no automatic way to prevent an
Entity from being deleted as long as it's still referenced. But you can always
implement this restriction in the ejbRemove callback method.
Foreign key constraints in the database prevent a referred row from being
deleted by raising an error. The EJB container especially provides managed
relationships and dependency management to prevent these errors.
Implementing the delete-restriction in your bean is much better than catching
and handling foreign key constrain vioaltions from the database.
-- markus.
"Naik, Vikram ( eBiz Mumbai )" wrote:
> Hi Markus,
>
> Thanks for your response.
> Yes, container does nullify the foreign key column(s) in Entity A. Now my
question is, say we want to restrict the deletion of B, as its being refernced
by Entity A.
> Currently we achieve that using the foreign key constraint at database level.
For such relations we define, foreign key constraints which restricts the
deletion on an entity as its being referenced.
> So are there any other ways to do so. If contianer can handle cascade delete,
shouldn't it be able to handle such similar constraints ??
>
> Vikram.
>
> -- --Original Message-- --
> From: Markus Fuchs [mailto:Markus.Fuchs@(protected)]
> Sent: Mon 11/1/2004 4:24 AM
> To: J2EE-INTEREST@(protected)
> Cc:
> Subject: Re: EJB CMP 2.0 and Referential Integrity.
>
>
>
> "Having a Many To One relationship between A and B means that the
foreign key must be defined in B's table"
>
> It's actually the other way round:
>
> Having a Many-To-One relationship between A and B means that the
foreign key column(s) are defined in A's table. Removing B must automatically
nullify A's foreign key column(s). The container guarantees this behavior, even
for
> one-way relationships.
>
> -- markus.
>
> Markus Fuchs wrote:
>
> > Hi Vikram,
> >
> > Having a Many To One relationship between A and B means that the
foreign key must be defined in B's table, so removing Entity B has no effect on
A's representation in the database. The EJB Spec. defines relationships to be
> > "managed", i.e. the container must remove Entity B from the
relationship to Entity A in memory. (See for instance EJB 2.1 Spec, sec. 10.3.7
.5).
> >
> > B's cascadeDelete setting or foreign keys in the database have no
influence on this behavior. The container will handle the described situation
automatically.
> >
> > Regards,
> >
> > -- markus.
> >
> > "Naik, Vikram ( eBiz Mumbai )" wrote:
> >
> > > Thanks for your response.
> > >
> > > Thats, true container does take care of cascade delete, but what
happens in the following scenario:
> > >
> > > Say we have a Many to One aggregate uni-directional CMR relation
between Entity A and Entity B.
> > >
> > > Now, if we try to delete Entity B which is still be referred/
referenced by Entity A, the container just deletes the Entity B. unless we
define a foreign key constraint at database level, that would restrict the
deletion.
> > >
> > > Can container handle this stiuation, even if we dont defined
foreign key constraints at database level ?
> > > Is this something that developer has to take care of ?
> > >
> > >
> > >
> > > -- --Original Message-- --
> > > From: Guy Katz [mailto:gkatz@(protected)]
> > > Sent: Sun 10/31/2004 7:54 AM
> > > To: J2EE-INTEREST@(protected)
> > > Cc:
> > > Subject: Re: EJB CMP 2.0 and Referential Integrity.
> > >
> > >
> > >
> > > if you use CMR
> > > referential intergrity is a built in part of the game.
> > > depending on the nature of your CMR definition
(multiplicity etc..)
> > > the container will take care of it as long as you call
your CMR methods.
> > >
> > >
> > > -- --Original Message-- --
> > > From: A mailing list for Java(tm) 2 Platform, Enterprise
Edition
> > > [mailto:J2EE-INTEREST@(protected)]On Behalf Of Naik,
Vikram ( eBiz
> > > Mumbai )
> > > Sent: Saturday, October 30, 2004 7:47 PM
> > > To: J2EE-INTEREST@(protected)
> > > Subject: EJB CMP 2.0 and Referential Integrity.
> > >
> > >
> > > Hello,
> > >
> > > What are the different ways to have referential integrity
for your data,
> > > when the persistence is done using EJB CMP 2.0 ?
> > >
> > > We are using database foreign key constraints along with
CMR to achieve the
> > > same ?
> > >
> > > Would appreciate all your thoughts on the above.
> > >
> > > Regards,
> > > Vikram.
> > >
> > > =========================================================
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> > >
>
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