EJB CMP 2.0 and Referential Integrity. 2004-10-31 - By Markus Fuchs
Back
"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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