I think I've stumbled across a bit of problem with the way NHibernate determines when things are dirty.

I have the following mapping file:

<class name="ServiceScheduleSubComponent, Application.BusinessObject" table="ServiceScheduleSubComponents">

<id name="Id" column="Id" access="nosetter.camelcase-underscore" unsaved-value="00000000-0000-0000-0000-000000000000">
<generator class="guid"/>
</id>

<discriminator column="Type"/>

<property name="NotApplicable" column="NotApplicable" access="nosetter.camelcase-underscore"/>
<property name="RequiringVerification" column="RequiringVerification" access="nosetter.camelcase-underscore"/>
<property name="Comments" column="Comments" access="nosetter.camelcase-underscore"/>
<property name="Disabled" column="Disabled" access="nosetter.camelcase-underscore"/>

<subclass name="IntegerServiceScheduleSubComponent, Application.BusinessObject" discriminator-value="Integer">
<property name="FailCount" column="FailCount" access="nosetter.camelcase-underscore"/>
</subclass>

<subclass name="BooleanServiceScheduleSubComponent, Application.BusinessObject" discriminator-value="Boolean">
<property name="Failed" column="Failed" access="nosetter.camelcase-underscore"/>
</subclass>

</class>

Now the trouble is that in both my subclasses the fields that are specific to them are Boolean and Int32 values. Unfortunately though, in my database I need to allow both fields to be nullable. That appears to mean that when NHibernate is trying to figure out if the values are dirty it always answers yes.

Any ideas as to how get round this?

Apologies.

It would appear that the problem I was having was by the "Disabled" property and not the 2 on the subclass. Specifically the database column allowed NULLs and member type was simply System.Boolean. Hence NHibnerate always thought that property was null... doh!

To fix I simply update the column on the database to be NOT NULL.