Re: [eclipselink-users] Discriminator and Inheritance.strategy

[christopher delahunt <christopher.delahunt@xxxxxxxxxx>]

Hello Michael

There is no way to know which subtables need to be joined without the 
discriminator field in the main table, and allows null rows in the 
subtable to be distinguished from null subtable results being null in 
the case an outer join or view is used.

Best Regards,
Chris.

Michael Simons wrote:
> Hello Guy,
>
> unfortunately we have the Inheritance.JOIN strategy.
> I don't understand why there's a discriminator needed for this strategy because which class an
> object is instance of is determined by the entry in the "sub"-table, isn't it?
>
> kind regards,
> Michael
>
> Guy Pelletier schrieb:
>   
> > A discriminator column is not needed for a TABLE_PER_CLASS strategy.
> >
> > The discriminator column is used to determine which class of object that
> > row represents.
> >
> > Cheers,
> > Guy
> >
> > ----- Original Message ----- From: "Michael Simons"
> > <michael.simons@xxxxxxxxxxx>
> > To: <eclipselink-users@xxxxxxxxxxx>
> > Sent: Friday, November 27, 2009 6:33 AM
> > Subject: [eclipselink-users] Discriminator and Inheritance.strategy
> >
> >
> >     
> > > Hello,
> > >
> > > I'm trying to port a client/server application first to JPA to enable
> > > the 3-tier migration.
> > > At the moment I try to use EclipseLink as JPA implementation.
> > > The first exception I fall over said "Unknown column 't2.DTYPE' in
> > > 'field list'"
> > >
> > > Seems like EclipseLink always needs a discriminator column even if the
> > > inheritance strategy is
> > > JOIN or TABLE_PER_CLASS.
> > > Is this correct?
> > > And if so, what is it good/needed for?
> > >
> > > [EclipseLink 1.2.0, database=MySQL 5]
> > >
> > > Kind Regards,
> > > Michael
> > > _______________________________________________
> > > eclipselink-users mailing list
> > > eclipselink-users@xxxxxxxxxxx
> > > https://dev.eclipse.org/mailman/listinfo/eclipselink-users
> > >
> > >       
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> >
> >     
>
>
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