Sending persisted JDO instances over GWT-RPC

Question

I've just started learning Google Web Toolkit and finished writing the Stock Watcher tutorial app.

Is my thinking correct that if one wants to persist a business object (like a Stock) using JDO and send it back and forth to/from the client over RPC then one has to create two separate classes for that object: One with the JDO annotations for persisting it on the server and another which is serialisable and used over RPC?

I notice the Stock Watcher has separate classes and I can theorise why:

• Otherwise the gwt compiler would try to generate javascript for everything the persisted class referenced like JDO and com.google.blah.users.User, etc
• Also there may be logic on the server-side class which doesn't apply to the client and vice-versa.

I just want to make sure I'm understanding this correctly. I don't want to have to create two versions of all my business object classes which I want to use over RPC if I don't have to.

Answer 1

The short answer is: you don't need to create duplicate classes.

I recommend that you take a look from the following google groups discussion on the gwt-contributors list:

http://groups.google.com/group/google-web-toolkit-contributors/browse_thread/thread/3c768d8d33bfb1dc/5a38aa812c0ac52b

Here is an interesting excerpt:

If this is all you're interested in, I described a way to make GAE and GWT-RPC work together "out of the box". Just declare your entities as: @PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "false") public class MyPojo implements Serializable { }

and everything will work, but you'll have to manually deal with re-attachment when sending objects from the client back to the server.

You can use this option, and you will not need a mirror (DTO) class. You can also try gilead (former hibernate4gwt), which takes care of some details within the problems of serializing enhanced objects.