I have an application that will be sending some complex data models to governement agencies via EDI. One requirement of the system is that once a message is accepted, we must maintain an accurate history for up to 7 years.

We've basically got a normalized domain model working with hibernate, but we want to implement "versioning" on many domain objects. For example, if we have a driver that is linked to a shipment and his home address changes (or any other member that gets transmitted to the government changes) we have to maintain accurate history of his old address (or name, drivers license, etc).

Another example is if you had a Invoice and it contained a list of Items. Even if the price member on an Item changes, all old invoices should maintain a history of the old price. Again, the same goes for most other members that would be present.

Does anyone have a strategy or design pattern for this type of system. The current solution we're looking at is having something like this as our base class:

public abstract class VersionedDomainObject implements VersionedObject {
private long id;
private boolean isActive();

public abstract VersionedObject getUpdatedVersion();
public abstract VersionedObject createNewVersion();

... getters and setters ...
}

Basically every new object would maintain a new version if one exists. This works great for simple cases, but doesn't work well for complicated cases with a bunch of many-to-one relationships. For example if I had an object like:

public class Foo extends VersionedDomainObject {
private String name;
private List<Bar> bars;
private Set<Whatever> whatevers;
....
}

When I want to make an updated version, I have a bunch of Bar and Whatever objects that are part of a many-to-one relationship with Foo, so I'd have to either create copies of all of them as well, or have a strategy link the objects as many-to-many relationships.

Anyway, does anyone have some experience solving this type of problem. I'm sure there is a nice elegant design, but I'm not seeing it at the moment.

Thanks

Does anyone have experience with this or some advice?

There are some good tools out there which will automatically modify your DB schema to add versioning / auditing and automatically add the triggers to all of the tables you specify. I don't have the names in front of me, but which you'll want is dependent on your database anyway. Some of them come with reporting and visualization tools, some don't.

Thanks... My database is PostgreSQL 8.1. I'm really looking for more of a design pattern that will work for me. I'm more concerned with making the domain model work well and persisting the "correct" implementation shouldn't be too big of a deal. I don't really want to use triggers for the type of "versioning" I'm talking about, but I'm interested in hearing anyones approach.

Thanks for the help!

If you haven't already, it's well worth having a look at this post in the NHbernate forum. It's the only way I can see to do this kind of versioning (as opposed to history tables) with hibernate.

http://forum.hibernate.org/viewtopic.php?t=955576