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From "Michael Gentry" <blackn...@gmail.com>
Subject Re: creating/saving transient objects to database
Date Fri, 22 Jun 2007 13:00:20 GMT
We had something similar here where a batch job needed to read a data file
and insert new records or update existing records (handle duplicates,
essentially).  What we did was:

* Read the data file, find the key data.
* Write and call a getFoo(dataContext, keys) method.
* The getFoo() method would query the database and if it found a record, it
would return the Cayenne object to us.  If no record was found, it would
create and register a new object in the DC and return the new object.
* Then we'd apply all the data in the data file to the object return by
getFoo().
* Then dataContext.commitChanges().
* Repeat until we processed all the data.

Seemed to work pretty well and I think that approach would work for you,
too, most likely.  In your case, your POJO is the equivalent of a record in
our data file.  This also frees you up from having to care about the
persistence state.  You don't care.  You have an object, apply the changes,
commit.

/dev/mrg

PS. If relationships are involved, your getFoo() should create all the
objects for all of the required relationships if you have to create/register
new objects (when there was no DB match).  This way your main processing
code can just apply changes blindly without having to check if the
relationships exist.


On 6/21/07, Michael Lepine <mikelepine@gmail.com> wrote:
>
> 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.
>

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