Inheritance Mapping Fluent NHibernate results in unnecessary joins - nhibernate

Question

The issue is when selecting directly on the base model the generated SQL performs an left outer select on the subclasses.
Basemodel.
public class Node
{
public virtual int ID {get;set;}
public virtual string Url {get;set;}
}
public class CMSPage : Node
{
public virtual string FieldA {get;set;}
public virtual string FieldB {get;set;}
}
public class Article : Node
{
public virtual string FieldC {get;set;}
public virtual string FieldD {get;set;}
}
My Mapping is
public class NodeMap : ClassMap<Node>
{
Table("Nodes");
Id(x => x.ID, "Node_ID");
Map(x => x.Url);
}
public class CMSPageMap: SubclassMap<CMSPage>
{
Table("CMSPages");
Map(x => x.FieldA);
Map(x => x.FieldB);
}
public class ArticleMap: SubclassMap<Article>
{
Table("Articles");
Map(x => x.FieldC);
Map(x => x.FieldD);
}
When querying direct on Nodes using ICriteria
var store = session.CreateCriteria(typeof(Node));
store.Add(Restrictions.Eq("Url", filter.Url));
store.SetProjection(Projections.ProjectionList()
.Add(Projections.Property("ID"), "ID")
.Add(Projections.Property("Url"), "Url"));
store.SetResultTransformer(new
AliasToBeanResultTransformer(typeof(Node)));
Node result = store.UniqueResult<Node>();
The sql generated is
SELECT this_.Node_ID as y0_, this_.Url as y7_ FROM Nodes this_
left outer join CMSPages this_1_
on this_.Node_ID = this_1_.Node_ID
left outer join Articles this_2_
on this_.Node_ID = this_2_.Node_ID
WHERE this_.Url = '/' /* #p0 - Url */
How do i prevent the join selects
Ive tried using both Abstract and KeyColumn according to https://www.codeproject.com/Articles/232034/Inheritance-mapping-strategies-in-Fluent-Nhibernat

Answer 1

Subclass mapping purpose is to have a Table per class hierarchy. Means you have one table for any child class. You can find examples on the documentation about all kind of supported inheritance by NHibernate.
I think you need to try "Table per subclass" strategy, using a JoinedSubclassMap<T>. The two subclass tables have primary key associations to the superclass table so the relational model is actually a one-to-one association. Documentation 9.1.2. Table per subclass
If you want to keep the SubclassMap<T> you must use a discriminator. 9.1.3. Table per subclass, using a discriminator.