nhibernate many-to-many with relationship specific properties

Question

Is there a way to map a many-to-many relationship with properties on each item in the list specific to the relationship? The actual case I'm trying to solve is this:

A business can be related to many contacts, and a contact can be related to many businesses. What I want to do is provide a status for the relationship, like active or deleted and a date the contact was invited (or added) to be a contact for that business. So say a contact can be active for one business, but pending for another business.

I know I can easily achieve this by just making the relationship an actual entity and mapping the association entity to the collections, but I REALLY hate doing that. It just feels dirty making something like a relationship an actual entity. What I'm wondering is if there's a way to map the relationship specific properties to each object. So, say I have the list of contacts for a business. Each contact in that list would have a status, but in the mapping it would make that status specific to the business. I was hoping I could do something like this in what would be the business mapping:

<bag name="Contacts" table="BusinessContactAssociations" lazy="true" cascade="all">
  <key column="BusinessID"/>
  <many-to-many class="Contact" column="ContactID">
    <join table="BusinessContactAssociations">
      <key column="ContactID"/>
      <property name="InvitedDate"/>
      <property name="Status"/>
    </join>
  </many-to-many>
</bag>

but of course that doesn't work, because join can't be used within a many-to-many, but it illustrates what I want.

Anyone have any handy nhibernate mapping magic for me?

Answer 1

As far as I know many-to-many is only used for using a typical two column join table. Given that you want to add properties to the relationship you would be better off mapping it as two separate one-to-many relationships with a join class (well it's more than that because it has its own properties but you know what I mean).

Update

This isn't nHibernate magic but there's nothing to stop you from using a join class that is private or otherwise hidden and then exposing the properties of the join class from your main classes.

Answer 2

You can use <map> to get ternary associations instead of your <many-to-many> mapping. You can then use <composite-index> to get value objects used as the key of the dictionary, if you want more than one property associate with the relationship. Check out Ayende's blog post for some example code.