We are designing a layered application - ui, domain, persistence,...
We also primarily work with interfaces. ie we pass interfaces around and variables to hold object reference are of type "Interface".

I have a "Client" which implements "IClient". I would like to restrict the reference to the Client implementation just to this - IClient aClient = new Client() in the domain layer. Also, We would like to keep all the NHibernate code in the persistence layer and we would like it to only know about the Interfaces.

In my mapping file (<>.hbm.xml) if I use the class name as "IClient" then Session.Save(aClient) chokes because it expects an object of type IClient while aClient is of type "Client".

To avoid this, if in my mapping file I use the class name as "Client" then the object constructed and returned by Session.Get<IClient>(ClientId) chokes because it only knows how to construct "Client".

So my question is this - in the nhibernate way of the world, is it possible to have a class implement an Interface and that Class/Interface is implemented as a single table in the db?

Other way to ask the question would be, is there any way I can convey the information to nhibernate that Client implements the interface IClient so it is appropriate interchange Client for IClient and vice-versa.

Ist should be popssible to implemet this with sub-class mapping.
I.e. You map IClient as class and Client as subclass.

Gert

I keep running into this Exception.

TestLayer.ClientTest.RetrieveAndUpdateClient : System.TypeInitializationException : The type initializer for 'Persistency.DbMgr' threw an exception.
----> NHibernate.MappingException : discriminator mapping required for polymorphic persistence

I tried different combination of values for the the discriminator value without luck. Can you please see what's wrong with the mapping as show here -
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"
namespace="Model.Interfaces"
assembly="Model.Interfaces">
<class name="IClient" table="cus" discriminator-value="Model.Client.Client">
<id name="Id" column="cusky">
<generator class="guid" />
</id>
<property name="FirstName" column="cus01frnm" />
<property name="LastName" column="cus01lanm" />
<property name="Status" column="cusstat" />
<property name="Change" column="`change`" />
<property name="Create" column="`create`" />
<subclass name="Model.Client.Client, Model.Client" extends="Model.Interfaces.IClient" discriminator-value="Model.Client.Client">

</subclass>
</class>

</hibernate-mapping>

This is a single class implementing an Interface and mapping to a single table so I do not really have a discriminating column as shown in most examples.

I have no idea if it possible to have subclass mapping without discriminator column. I would think that not.

Gert