Re: [eclipselink-dev] Facilitating migration from Toplink / Toplink Esse

[Mitesh Meswani <Mitesh.Meswani@xxxxxxx>]

As I mentioned below, EclipseLink would accept Essentials provider class 
only if Essentials is not available in classpath. This assumes that if a 
user intended to run with Essentials, he would have made Essentials 
visible to application else he is trying to migrate from an environment 
where he relied on Essentials into an environment that only has 
EclipseLink.

This is a kludge and I personally dislike it. However, this is the only 
way I see to facilitate users migrating from an environment that had 
Essentials to EclipseLink without them manually updating their app.

Thanks,
Mitesh

Gordon Yorke wrote:
> This is an error case as the user has explicitly asked for Essentials 
> and EclipseLink will not care if Essentials is available or not.  If 
> EclipseLink were to accept the Essentials provider how would a user 
> run Essentials applications in V3? --Gordon
>
> Mitesh Meswani wrote:
> > Hi Gordon,
> >
> > Overriding provider is for the case where user has explicitly 
> > specified provider as Toplink but running in an environment where 
> > only EclipseLink is available.
> >
> > Thanks,
> > Mitesh
> >
> > Gordon Yorke wrote:
> > > There should be no need to override the provider as the provider is 
> > > only specified if a user wants a specific provider as by default 
> > > there is no provider specified.  Using the essentials properties as 
> > > eclipselink properties would be a good idea.
> > > --Gordon
> > >
> > > Tom Ware wrote:
> > > > I like part 1 of the proposal.
> > > >
> > > > I do not think that EclipseLink itself should allow itself to be 
> > > > selected as the JPA provider when the user has specifically chosen 
> > > > TopLink Essentials.  To me, if a user requests a specific JPA 
> > > > provider another provider should not allow itself to be selected.  
> > > > Perhaps this is something that should be done within GlassFish 
> > > > rather than within EclipseLink.
> > > >
> > > > -Tom
> > > >
> > > > Mitesh Meswani wrote:
> > > > > *Background*
> > > > > Currently, an app using Toplink / Toplink Essentials as JPA 
> > > > > provider (and not using any of provider specific features in 
> > > > > code), will still need to be manually modified by user to change 
> > > > > persistence.xml for property names from toplink.* to eclipselink.* 
> > > > > and provider name from 
> > > > > oracle.toplink.*.EntityManagerFactoryProvider to 
> > > > > org.eclipse.persistence.jpa.PersistenceProvider. We know that 
> > > > > EclipseLink has a migration tool that helps user with this. 
> > > > > However, using the tool would require manual steps from user. It 
> > > > > might not be possible/convenient for many users to change their 
> > > > > packaged application (like .ear and .war) for this. This issue 
> > > > > came up during discussion about upgrade from GlassFish V2 to V3
> > > > >
> > > > > *Proposal
> > > > > *1. We translate the property names and provider during deploy. 
> > > > > This would help ease migration from Toplink to EclipseLink for 
> > > > > majority of  JPA users who would mainly be using toplink.jdbc.* 
> > > > > properties in their persistence.xml.
> > > > > 2. We accept oracle.toplink.*.EntityManagerFactoryProvider as a 
> > > > > supported class name
> > > > >
> > > > > To be more specific, for 1 above, we enhance 
> > > > > EntityManagerSetupImpl#deploy() to translate old toplink 
> > > > > properties in addition to translation that it is doing now. For 2 
> > > > > above, we enhance 
> > > > > JPAInitializer.isPersistenceProviderSupported(String className)  
> > > > > to accept oracle.toplink.*.EntityManagerFactoryProvider as a 
> > > > > supported provider. To facilitate the use case where a user 
> > > > > explicitly wants to use Toplink, we can try to be clever in 
> > > > > accpeting toplink as a supported provider only if Toplink is not 
> > > > > found in classpath.
> > > > >
> > > > > I can work on implementing this. Please reply with your 
> > > > > thoughts/comments.
> > > > >
> > > > > Thanks,
> > > > > Mitesh
> > > > >
> > > > >
> > > > > ------------------------------------------------------------------------ 
> > > > >
> > > > >
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