Hi. I'm having problems mapping a ternary association. I have 3 classes: Product, Notification and Subscriber. For a given Product and Subscriber, I want a list (or better, a set) of Subscribers. I thought of modeling this as a <map> in Product as following:



but it seems this mapping is only good for getting one Subscriber (given the Product and the Subscriber, which is the key of the map)

So, how do I model this association? I'd really really like to use <map> since it's much easier than sets of composite-elements or things like that...

Of course I have ISubscriber and INotification correctly mapped.

I'm using NHibernate 1.0.1.0 with MSSQL 2000

TIA

Mauro

Oops! Correction:
For a given Product and Subscriber, I want a list (or better, a set) of Notifications

hmmm... many people had the same problem and none got it solved:

http://forum.hibernate.org/viewtopic.php?t=933592
http://forum.hibernate.org/viewtopic.php?t=932376
http://forum.hibernate.org/viewtopic.php?t=929036

any ideas?

The problem seems to be one with the Hibernate docs, which make no distinction between the "type" of ternary relationship modelled by each suggested form of mapping. Using a map with an index-many-to-many is a "limited" ternary relationship: given element-types A, B and C, there will be one and only one C for each A-B pair. If you need an "open" ternary relationship, you'll have to use the composite-element mapping (see the last code example in this section).

However, it appears that what you really want is a map (hashtable, keyed on Subscriber) of sets of Notifications. I may be wrong, but I don't think there is any way to natively map this in NHibernate. You may still be able to provide the desired semantics in your business objects, however, while maintaining the necessary structures for persistence behinds the scenes.

Thanks, that's what I meant, a map of sets. What I did was map the relation as a set and then wrap the set with a class implementing IDictionary. It sucks for queries, since it's O(n), but it works...