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From Andrus Adamchik <and...@objectstyle.org>
Subject Re: Selective commit
Date Mon, 07 Jan 2008 13:31:35 GMT
Hi Álvaro,

It is hard to give a precise advice on multithreading without knowing  
the nature of your application. So here is a few general notes:

* DataContext instance is your isolated area for making in-memory  
changes to objects that will all be committed at once. So consider  
using multiple contexts as appropriate. Cayenne docs recommend various  
common patterns, such as DataContext per session (i.e. each user has a  
dedicated context), DataContext per request, or DataContext per  
application (in a read-only app). You can also devise your own  
approach, if none of the above fit your needs. All you need to know  
here is that multiple threads *reading* from a shared DataContext is  
ok, but multiple threads *writing* to a shared DataContext is not ok.

* In a rare case if you really need multiple threads to work off of  
the same context, consider using a dedicated nested DataContext for  
each atomic object modifications.

Andrus


On Jan 7, 2008, at 2:44 PM, Álvaro Martínez wrote:
>
> Hi, I've been working for a while with Cayenne but never realized I  
> had a problem... until I got a weird exception.
>
> The fact is that I had been using context.newObject() and  
> context.commitChanges() to create new rows in the database. But my  
> application works with many threads, so global commits can (and in  
> fact do) interrupt normal creation of objects. Thread A and Thread B  
> are creating objects and filling their fields, but then B commits  
> all and A throws a validation exception because mandatory fields are  
> missing.
>
> How could I commit only one object?
>
> Thanks,
>
> Álvaro from Spain (Push the button Inc.)
>
>
>


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