NHibernate Polymorphic Mappings
I have an interface IUserLocation
and a concrete type UserLocation
.
When I use ICriteria by specifying an interface IUserLocation
, I want NHibernate to instantiate a specific type UserLocation
.
I created an HBM mapping file using the type-specific table strategy (shown below). However, when I query NHibernate using ICriteria I get:
NHibernate cannot instantiate abstract class or interface MyNamespace.IUserLocation
Can anyone understand why this is the case? (source code for the corresponding NHibernate bit is here (I think))
My ICriteria:
var filter = DetachedCriteria.For<IUserLocation>()
.Add(Restrictions.Eq("UserId", userId));
return filter.GetExecutableCriteria(UoW.Session)
.List<IUserLocation>();
My mapping file:
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-lazy="true">
<class xmlns="urn:nhibernate-mapping-2.2" name="MyNamespace.IUserLocation,MyAssembly" abstract="true" table="IUserLocations">
<composite-id>
<key-property name="UserId" column="UserId" type="System.Guid"></key-property>
<key-many-to-one name="Location" column="LocationId" class="MyNamespace.ILocation,MyAssembly"></key-many-to-one>
</composite-id>
<union-subclass table="UserLocations" name="MyNamespace2.UserLocation,MyAssembly2">
<property name="IsAdmin" />
</union-subclass>
</class>
</hibernate-mapping>
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From the documentation, it looks like your mapping file should do this with me. However, I have never tried a table for a specific class. And I notice examples in the NHibernate documentation as it doesn't use interfaces for the base class. Perhaps this is not supported?
I used Table for a specific class using implicit polymorphism before with a separate mapping for each subclass.
<class name="MyNamespace.UserLocation,MyAssembly" table="UserLocations">
...
</class>
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