[forge-dev] @GeneratedValue Strategy

[Rafael Pestano]

I think IDENTITY strategy is not supported by all databases..

2012/5/4 Ryan Bradley <rbradley at redhat.com>

> Okay, so say we have two different entities in our scaffolded webapp,
> Customer and Account.  Under the current GenerationStrategy:
>
> I create a Customer object, and that will have an ID of 1.
>
> I create an Account object, and that will have an ID of 2, even though
> it is the first (and only) Account in the database.
>
> Using GenerationStrategy.IDENTITY, both objects will have identities of
> 1, i.e. there are separate sets of IDs kept for each table in the
> database.  One useful case that I can think of is that, in the Spring
> scaffold implementation, individual objects can be navigated to in the
> URL using their ID (e.g. /customers/1 would go to the Customer object in
> the database with an ID of 1).  Therefore, it might cause confusion if a
> user was trying to navigate using the URL but not necessarily knowing
> the ID of the object they are looking for (even if they know its ID
> relative to other objects of the same type).
>
> Does that clarify things?
>
> Cheers,
> Ryan
>
> On 05/04/2012 10:19 AM, George Gastaldi wrote:
> >> Thinking of scaffold implementations, it might be best if a separate set
> >> of IDs was generated for each separate entity.
> > I don´t think I get it. Can you give a practical example ?
> >
> > Regards,
> >
> > George Gastaldi
> >
> > 2012/5/4 Ryan Bradley<rbradley at redhat.com>:
> >> Greetings all,
> >>
> >> Currently, the entity plugin annotates the ID primary key with
> >> @GeneratedValue.  This annotation uses the default generation strategy,
> >> GenerationType.AUTO, to generate the values for this key.  Using this
> >> strategy, the same set of values is used for all entity tables.  In
> >> other words, you cannot have two entities with the same value for ID, as
> >> it is incremented with each entity creation rather than with each
> >> creation of an entity of a specific type.
> >>
> >> Thinking of scaffold implementations, it might be best if a separate set
> >> of IDs was generated for each separate entity.  I believe that this can
> >> be accomplished by annotating the field with
> >> @GeneratedValue(strategy=GenerationType.IDENTITY).  I was thinking of
> >> modifying the ScaffoldPlugin to change the GenerationType on this
> >> annotation in the generateFromEntity method (from-entity command).
> >>
> >> Any objections to this change?
> >>
> >> Cheers,
> >> Ryan
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Rafael M. Pestano

Desenvolvedor Java Cia. de Processamento de Dados do Rio Grande do Sul
Graduando em Ciência da Computação UFRGS
http://code.google.com/p/jsf-conventions-framework/
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@realpestano
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