Hi Adam,
On Aug 9, 2006, at 4:05 AM, Adam Bien wrote:
> I discussed the following idea already with craig at the JAOO 2005.
>
> Problem:
>
> If you detach a persistent entity send it to client, then back, the
> "before image" is lost.
> In this case you need a version number or timestamp. You can have a
> problem, in case you are working with a legacy database - it is
> often hard or not allowed to change the schema.
>
> Now the following idea: why not send the before image together with
> the entity?
> As a improvement also only the where statement could be sent over
> the wire. This should be sufficient to detect the collisions,
Yes, sending the before-image across and maintaining the change list
in the detached entity would allow you to compare the columns in the
database with the fields in the before-image (in the WHERE clause of
the UPDATE statement).
Of course, this would require using a serialization protocol that
sends change information along with the state. Which implies that you
have a specialized readObject/writeObject on both ends of the
serialization. Which implies that you cannot use the POJO class as-is
unless you provide this specialized serialization behavior as part of
your class definition, or have your persistence provider enhance the
class before use, and install the enhanced class on both client and
server.
>
> I'm not sure, whether this list is the right place to discuss the
> things - but I think such a feature would be unique...
It's as good a place as any...
Craig
>
> greetings,
>
> adam
>
> --
> Dipl. Inf. adam bien
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> entwickler.press 2006
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Craig Russell
Architect, Sun Java Enterprise System
http://java.sun.com/products/jdo
408 276-5638 mailto:Craig.Russell_at_sun.com
P.S. A good JDO? O, Gasp!
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