I have a readonly backing field of Ilist which is exposed with a property IEnumerable. The backing field does not get initialised, but the IEnumerable List does and ends up pointing to an NHibernate collection as it should.

The problem occurs in the subclass RootTemplateItem only. The mapping is created by fluent and automapping, so I was wondering if anyone with more hbm.xml experience could check the map.

<bag access="nosetter.camelcase-underscore" cascade="all-delete-orphan" inverse="true" lazy="true" name="SubItems" mutable="true">
<key>
<column name="Parent_id" />
</key>
<one-to-many class="DTE.Business.Domain.Model.Forms.AssessmentTemplate.TemplateItem, DTE.Business, Version=0.0.2.0, Culture=neutral, PublicKeyToken=null" />
</bag>

<joined-subclass name="DTE.Business.Domain.Model.Courses.RootTemplateItem, DTE.Business, Version=0.0.2.0, Culture=neutral, PublicKeyToken=null" table="DTE_RootTemplateItem">
<key>
<column name="TemplateItem_id" />
</key>
<bag access="field.camelcase" cascade="all-delete-orphan" inverse="true" lazy="true" name="SubItems" mutable="true">
<key>
<column name="Parent_id" />
</key>
<one-to-many class="DTE.Business.Domain.Model.Forms.AssessmentTemplate.TemplateItem, DTE.Business, Version=0.0.2.0, Culture=neutral, PublicKeyToken=null" />
</bag>
<many-to-one access="backfield" class="DTE.Business.Domain.Model.Courses.AssessmentTemplate, DTE.Business, Version=0.0.2.0, Culture=neutral, PublicKeyToken=null" name="Template">
<column name="Template_id" />
</many-to-one>
</joined-subclass>


protected readonly IList<TemplateItem> _subItems = new List<TemplateItem>();

public virtual IEnumerable<TemplateItem> SubItems
{
get
{
return _subItems;
}
}

This turned out to be caused by the property returning a proxy which was of the base type, not the actual type and somehow therefore not correctly intializing the collection?? However the proxy type not returning the correct type is a known issue \ feature caused be limitations of .net and a reluctance on my part to create meaningless interfaces to cover every type in my domain just to satisify Nhibernate :)