Hibernate version:
HB3

Hi all,

I am trying to use a discriminator with a formula. I can see how the formula is used to evaluate what class to instantiate, but what is supposed to happen in the reverse direction, when saving a new persistant class?

example:
<discriminator
type="java.lang.String"
formula="case when Org_Type in ('A', B') then 'A' else 'C' end"
/>

If I try to persist an instance of the sub-class that should have a discriminator value of 'C', how would hibernate know to set the Org_Type column? I tried adding in the column attribute to the <discriminator> tag, but all examples I've seen either use "formula" or "column", but not both.

The problem I am getting when saving new objects is: cannot insert the value NULL into column 'org_type'. Hibernate does not seem to be populating the discriminator. Everything works fine if I don't use the formula, but I need this to support multiple discriminator values for one of my sub-classes.

I will post more details (mapping files, etc) if needed, but I would just like a general indication of whether this is supposed to work or not.

thanks very much,
Daniel.

<property name="orgType" column="org_type"/>

Thanks Christian, I knew I had to be missing something simple for such a fundamental thing to not be working :)

I assume you are saying that when using a discriminator with a formula, I need to expose the discriminator property and set it manually before saving the persistant objects?

When I use a discriminator without a formula, I don't need to do that, I know that for sure.

Is this correct? It might be worth an explicit mention in the online docs.

thanks again,
Daniel.

Thanks , all

I met same problem when use formula in discriminator.

I will try it by christian's suggestion.

-Vincent

Uh guys, I don't know what you think discriminator formula does. But take a step back and ask yourself: If discrimination is based on literal values that can be expressed using discriminator-value attributes in subclass mappings, why are you trying to use a complex expression (formula) to calculate it? You don't need formula at all then.

And of course you have to maintain whatever fields you will use in a formula yourself.

Yes, my discriminator values are simple literals, but one of my subclasses can have one of two valid discriminator values, which (I *think*) means I need to use a formula (or creating an extra redundant subclass may be another option).

It may seem obvious to you guys that using a formula means having to maintain the discriminator values ourselves, but the docs don't mention anything about this at all when moving from simple discriminators to formula-based ones.

Of course once you think about it, it is very obvious, because Hibernate would have no way of knowing how to maintain the discriminator, which is why I tried using both the column and formula attributes.

Regardless, thanks heaps for the help, I got exactly the info i was after :)

Daniel.