ODMG and primary key assignment

[Saleem Shafi <sa...@gmail.com>]

Hello,

i have a quick question about when a primary key is assigned to an
object using the ODMG interface provided by OJB..  i realize that the
PersistentBroker.store() method will set the primary key property on
the object, but the .lock() method on the ODMG transaction doesn't
seem to do that for me..  i understand that the transactions are
different between OJB and ODMG and that the object will get its ID
after the ODMG transaction commits, but is there any way to get the ID
assigned before that?


Saleem.

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Re: ODMG and primary key assignment

[Armin Waibel <ar...@apache.org>]

Saleem Shafi wrote:

> Hello,
> 
> i have a quick question about when a primary key is assigned to an
> object using the ODMG interface provided by OJB..  i realize that the
> PersistentBroker.store() method will set the primary key property on
> the object, but the .lock() method on the ODMG transaction doesn't
> seem to do that for me..  i understand that the transactions are
> different between OJB and ODMG and that the object will get its ID
> after the ODMG transaction commits, but is there any way to get the ID
> assigned before that?

No and yes ;-)
Internally OJB use an unique Identity object (Identity.java) for each 
persistent object. Identity objects based on the PK and the top-level 
class of the object and the PK for new persistent objects are assigned 
when the Identity object was created. So yes, it is possible to assign 
the PK before an persistent object was stored (creation of an Identity 
object assign the PK for new persistent objects).
But this is not possible when using native DB Identity columns for your 
persistent objects (hsql, mysql, mssql,... support Identity columns). In 
that case the PK was set by the DB on persistent object insert and the 
PK can only extract after insert of the persistent object. OJB use in 
that case a temporary PK for Identity objects created before the 
persistent object was stored. Thus the answer is no, it's not guaranteed 
that you get the real assigned PK before the object was stored.

regards,
Armin



> 
> Saleem.
> 
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> 
> 

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Re: ODMG and primary key assignment

[Brian McCallister <mc...@forthillcompany.com>]

To my knowledge there isn't, though it should be possible to implement 
(outside of ODMG, as I don't think ODMG provides a mechanism in its 
API).

I am not sure how much rework of internal API's would be required, but 
as (in most cases) OJB assigns the PK itself it could be possible to do 
it early. I don't have a lot of spare cycles to dig into doing this 
right now, however.

-Brian

On Jul 26, 2004, at 3:38 PM, Saleem Shafi wrote:

> Hello,
>
> i have a quick question about when a primary key is assigned to an
> object using the ODMG interface provided by OJB..  i realize that the
> PersistentBroker.store() method will set the primary key property on
> the object, but the .lock() method on the ODMG transaction doesn't
> seem to do that for me..  i understand that the transactions are
> different between OJB and ODMG and that the object will get its ID
> after the ODMG transaction commits, but is there any way to get the ID
> assigned before that?
>
>
> Saleem.
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: ojb-user-unsubscribe@db.apache.org
> For additional commands, e-mail: ojb-user-help@db.apache.org
>
>



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