Hi,

I'm writing a distributed application using hibernate. Because all parts of the application should be able to work offline, every part has an own database.

Now I'm writing a framework to distribute data to all parts of the application. My idea is to send hibernate-mapping-objects between the parts and just to commit the actions at the destination.

For this case I have to avoid generated primary-key ids. Can you think of any other restrictions? What do you think at all about the idea?

Best regards Michael

Using hibernate for mass insertions is SLOOOOOOOW!

You also have to deal with concurrency issues.
For example:

Table A:
- id (number)
- whatever else

Table B:
- id (number)
- aReference (references id of A)

Now if you read in all of table A and blast it over to another database, then do all of table B, you have a problem: What happens if a transaction inserts a record pair (A and B) along the way?
You've already read table A, so you don't have the A reference, but when you copy over table B, the foreign key will expect the record in A! Oops!


Most real databases have replication tools available which deal with this issue and more. They're also much faster than reading/writing records in a Java application. Use the right tool for the job.

OK, I think I didnt choose my words wisely. I dont want to replicate the database, I want to synchronize some data. There are only some data, that have to be synchronized, so its not enough to do a whole replication.

One possibility was to define my own object to store all the data of the hibernate object, send this own defined object to the other application, build the new hibernate object and do an update by this object.

Or I could just serialize the hibernate object as it is, send this to the remote application and do the update by this object.

The second possibility would be much less work. But I can imagine, that there are some tricky things to regard (like not using hibernate generated keys).

So should I do the extra work and define some new classes to send objects over the network or can I send the hibernate objects?

Best regards Michael

You'll want to be careful serializing beans obtained through Hibernate, as they also contain Hibernate specific info.

One idea would be to make your POJOs serializable, then use http://jakarta.apache.org/commons/beanutils/ to copy the properties (Using BeanUtils.CopyProperties http://jakarta.apache.org/commons/beanutils/commons-beanutils-1.7.0/docs/api/org/apache/commons/beanutils/BeanUtils.html#copyProperties(java.lang.Object,%20java.lang.Object)) from the hibernate bean to your fresh bean before serializing it.

Well, I already wrote an app using RMI and sending objects created by Hibernate to the client. The only problem I ever encountered was the lazy-loading: obviously, you will have to take care about not trying to use lazy-loaded properties on the other side.

Apart from this, I don't think there's a something special to watch out about sending your H3 POJOS. Just make them serializable, send them and read them (and rule them all :-p).