NHibernate many-to-one association refuses to load - nhibernate

Question

I have the following mapping, the many-to-one property 'Message' has a corresponding one-to-many association in the 'RootMessage' class.
<class name="IMessageReceipt" lazy="false" table="MessageReceipts" abstract="true">
<id name="Id">
<generator class="guid.comb"></generator>
</id>
<discriminator column="Discriminator"/>
<property name="Address" />
<property name="Status" />
<property name="MarkedAsDeleted" />
<many-to-one name="Message" column="MessageId" class="RootMessage"
not-found="ignore"/>
<subclass name="MessageReceipt" lazy="false" discriminator-value="1">
</subclass>
</class>
The many-to-one association refuses to load when using the criteria api (all I get is NULL), here is an example of a query:
List<IMessageReceipt> list;
using (var tx = Session.BeginTransaction())
{
var criteria = Session.CreateCriteria(typeof (IMessageReceipt));
criteria.Add(Restrictions.Eq("Address", address));
criteria.Add(Restrictions.Eq("Status", status));
criteria.SetFirstResult(0);
criteria.SetMaxResults(quantity);
list = criteria.List<IMessageReceipt>().ToList();
tx.Commit();
}
return list;
Any ideas?

Answer 1

Ok so after almost a day of chagrin I have the solution. NHibernate doesn't automatically assume a bi-directional association between two entities even if you have mappings between both. You need to imperatively declare the associations in your code before persisting. Thus:
message.Receipts = receipts;
foreach (var receipt in receipts)
{
receipt.Message = message;
}
Session.Save(message);
tx.Commit();
Also inverse="true" should be applied to the side with the collection member:
<set name="Receipts" inverse="true" cascade="save-update">
<key column="MessageId"></key>
<one-to-many class="IMessageReceipt"/>
</set>