Hi All,
Have a question regarding the mapping of class hierarchy. Let's say (hypothetically) that we have an Owner class that has a reference to a Vehicle interface. There are 3 implementation classes of Vehicle: Car, Truck and Wagon. All information is stored in one table: VehicleReg.
So we have the following hibernate mapping:

<class name="Owner" table="VehicleReg">
.....
<discriminator column="VehicleType"/>
<component name="vehicle"... ?
</class>

How do I tell Hibernate that it needs to create an implementation of Vehicle depending on the discriminator. And can we use a composite discriminator (i.e look at values not in one but in two columns)?
Any help would be greatly appreciated
best regards,
Evgueni

Inheritance/polymorphism is not supported for components. You could try using a CompositeUserType, perhaps. Not sure if it would help.

That is, I think, the third person that's asked for this that I've seen since you told me no-one ever wants to do it.

So, if I wrote a patch to do it (assuming I'm capable of doing that) would you accept it?

I'm keen on it because I really do think it's the best way to map some of these structures.

If you did decide that you would accept it as a patch (or even if not), do you think it would be hard to do?

Cheers,
Shorn.

I would accept a patch that did not require changes to core code (or that required only very simple changes).

I think it could be done by implementing AbstractComponentType, or modifying ComponentType, together with very minor changes to the mapping metamodel.

Hi,

I am also interested on having polymorphic components so my questions are :
- Shorn, did you manage to create a patch for that ? If not, do you have any idea on how this could be achieved ?

Here is a case where this feature would help me.
I have a Client object. I have different levels of clients : NewClient, GoodClient, GoldClient. I want some polymorphism on my levels to be able to define different behaviour on different client level. I also don't want to create a new Client object when the level of my client change.
Thus I have this classes :


As clients and levels are thightly coupled, I want to save them on the same db table. So, as far as I know, I have to make the level a component of the client class. This leads to the need of a subcomponent.

I present you this example because maybe I missed something in hibernate and it is possible to have all this classes mapped on one table. But if no, subcomponents seems to be a really useful feature

Seb