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From "Scott Anderson" <sander...@airvana.com>
Subject RE: Using Cayenne in GWT wthout DTOs
Date Wed, 17 Sep 2008 18:04:18 GMT
This topic has been discussed in this group before, but I'll reiterate
the general concepts. You can't serialize persistent objects, period.
There are many reasons why, but I don't have time to list them all, so
here are the three that are most important in my mind.

Reason #1:
In order for the GWT compiler to transform your CayenneDataObjects in to
JavaScript, it would have to resolve a graph that would encapsulate the
entire Cayenne library. I could list the reasons why you can't do that,
but I don't have time to write an essay right now, so save yourself the
headache by taking me at my word when I say it won't work.

Reason #2:
The purpose of the server-side code is to enable validation and
authentication. You can expose un-verified, un-authenticated database
access to the client-side code without RPC. If you're not going to
validate or authenticate, don't bother introducing the proxy. Cayenne
will work just as well in a stand-alone application -- the Modeler is a
good example of that.

Reason #3:
By writing the code to copy information out of beans and in to the
CayenneDataObjects, you will be forcing yourself to plug any validation
holes you would otherwise surely forget. Additionally, by using beans
targeted to the needs of your operations, the amount of data that is
required to go back and forth through the RPC tunnel will be
substantially lower.

If you were to serialize the CayenneDataObjects, which is impossible,
then for *every* operation you'd have to send the entire graph of the
object in question -- which is probably the entire database if you
reverse-map your relationships.


Hope this helps,
Scott

-----Original Message-----
From: Chanda Fake [mailto:chanda@lusakatimes.com] 
Sent: Wednesday, September 17, 2008 1:07 AM
To: user@cayenne.apache.org
Subject: Using Cayenne in GWT wthout DTOs

Hi

I have seen from the mailing list that some people have used Cayenne
with
GWT successfully.What is the best way to expose Cayenne model to GWT
without
using DTOs which I consider as duplication of work. Am trying to use my
Cayenne domain objects in GWT and running into some  usual issues GWT.
Am
thinking if there is a way to create a module with the offending class
"CayenneDataObject" and then including it using <inherits ..>. What have
others done.

Thanks in advance

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