Could anyone suggest how I should map the following. I have two tables, Clients and Freightpayers which map to a Client class and a Freightpayer class respectively. The tables are linked in a one-to-one relationship, sharing the same primary keys. In each case the key consists of two columns, Prefix char(2) and ID int. These map to a value class of type DBKey in the application. In the client table, ID is an identity (*) and in the Freightpayer the key is assigned to match the Client.

My question is, is there a way to map the above such that I get the same behaviour I'd get for single column keys, using the generator=foreign attribute for the freightpayer? The composite-id element doesn't have a generator attribute so I can't set it directly.


(*) the identity in the Client composite-id is not a problem. I've written a customer persister, along with a couple of (very) small mods to the nhibernate sources to support it.

Kev

a solution would be to use a id of a custom user type and assign it
using the "assigned" generator class

something like this
<id type="compositeType">
<generator class="assigned"/>
</id>

and make sure you assign this id immediately after you save

the custom user type should be a combination of the two types

i don't know if this will help, it's just an intuition...

I thought that was what I was currently doing to be honest, though with a different mapping than the one you gave:



Can you point me at some info on the mapping you provided, if it's different?

I was really hoping to get away from manually assigning the key. I feel I should be able to set the Client property of the Freightpayer and the key would be set.

Kev

Specifically, it's this part of the documentation I'm struggling with when it comes to composite ids:





I'm not sure how to specify the equivalent of "foreign" for a composite-id

Hi Kev,

I'm not sure if this is the situation you are asking about, but the documentation states that you can only use 'assigned' identifier when they are composite:

http://www.hibernate.org/hib_docs/nhibernate/1.2/reference/en/html/components.html#components-compositeid



Regards,
Richard

Hi Richard,

Ah, I was aware of that issue with regards to identities (in fact I've written a new persister which overcomes this, and lets a composite key use generated IDs), but I didn't realise it applied to foreign key relationships as well. Are you sure of the above, out of interest? I can see that setting the Client property of the Freightpayer is analagous to assigning the identifier anyway, so I wonder if it might be different.

Kev

Hi Kev,

The docs also say:




Um ... not 100% to be fair ... maybe 67.3%? :-)


Agreed. Another option might be to simply ignore the 'setting' of IDs. For example:


Regards,
Richard

you should try not to use composite-key mapping, it's nasty and
it's not a 'best practice'

Yes, I'm happy with that, and that side of it all seems to work. I guess largely I'm thinking from an aesthetic (?!) point of view that having to set both the Client property and the ID seems ugly, and that there's enough metadata there for NHibernate to be able to do it itself.



Ah, now that's an interesting idea - i'll take a look at where it gets me.

Kev

Ah, would that it were so easy. Unfortunately this is a legacy application. The database runs to a few hundred tables, and contains in the region of 2000 stored procedures. We need to rewrite the front end in such a way that both it and the existing front end can coexist during the transition period. If I could do away with the composite keys without breaking anything I'd do it like a shot, but it's not an option

Kev