[forge-dev] @GeneratedValue Strategy

[Ryan Bradley]

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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