Re: AW: creating/saving transient objects to database

Fri, 22 Jun 2007 14:46:12 -0700 


On Jun 22, 2007, at 12:30 AM, Peter Schröder wrote:
this approach has the downside that you may run into concurrency issues (check than act). 
you may get a duplicate even if you first check for an existing entry.
this is really tricky in webapplications...
You can overcome this by running the transaction in serializable mode. This will put read locks on ranges to prevent other transactions from inserting records that you are inserting after querying. 

Craig


kind regards,
peter

-----Ursprüngliche Nachricht-----
Von: Fredrik Liden [mailto:[EMAIL PROTECTED]
Gesendet: Freitag, 22. Juni 2007 00:10
An: [email protected]
Betreff: RE: creating/saving transient objects to database

If you're calling newObject you'll get a registered object with
PersistenceState.NEW. so consequently the commit tries to insert it.

I'm thinking at some point you'll need to manually check if the object
exists in the database or not based on some criteria. Maybe you can
create a service class that checks using a query if the Pojo object
exists in the db. If it does it returns the existing DataObject and if
not it returns the object using newObject. Then the persistenceState
will be either NEW or COMMITED and commit will trigger insert and update 
respectively.
Of course the Cayenne guys probably have some other nifty way to do it. 

Fredrik



-----Original Message-----
From: Michael Lepine [mailto:[EMAIL PROTECTED]
Sent: Thursday, June 21, 2007 2:46 PM
To: [email protected]
Subject: creating/saving transient objects to database

I've got a situation where I've got strict POJO objects that I'll need
to
copy data from and into my generated Cayenne classes. My issue is that
when
I copy the data from the bean to the Cayenne class, I don't know whether 
the
object exists or not. Thus, I create the Cayenne class instance using
DataContext.newObject(). Obviously, when I call
DataContext.commitChanges(),
an insert is being attempted on the corresponding table even if a record 
already exists in the database.

Is there a way to create the Cayenne instance so that the persistent
layer
will know to check whether the record exists and update it instead of
always
attempting an insert?

Any help and guidance are appreciated.


Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!

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