Question

TL;DR version: The code below gives me a “Association references unmapped class” exception when building the SessionFactory. What should be changed in the code to fix it?

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Even though Ayende @ Rahien doesn’t recommend using mappings to generic classes in this 2007 article I still had a go at it. I used the approach he mentioned. First the bit that is working:

<class name="Review`1[Person]" table="Review">
  <id name="Id" column="ReviewId"><generator class="native" /></id>
  <property name="Rating" />
  <many-to-one name="Subject" column="PersonId" class="Person" />
</class>

The corresponding generic class looks like this:

public class Review<T> : BaseEntity where T : IReviewable
{
    public virtual int Rating { get; set; }
    public virtual T Subject { get; set; }
}

This is working, and I can load these Review entities and show them in my MVC views no problem. The nice part is that my Subject will have the correct type when I use it in the controller and view.

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However, when trying to map a collection of Review items on my Person class things start to break down. Here’s the mapping I’m currently using:

<class name="Person">
  <!-- abbreviated -->
  <bag name="Reviews" table="Review">
    <key column="PersonId"/>
    <one-to-many class="Review`1[Person]" />
    <!-- Also tried these:
    <one-to-many class="table="Review"> 
    ... plus a few variations with fully qualified names ...
    -->
  </bag>
</class>

With this (abbreviated) class:

public class Person : BaseEntity, IReviewable
{
    /* Abbreviated */
    public virtual IList<Review<Person>> Reviews { get; set; }
}

This ends with an exception while building the SessionFactory:

Association references unmapped class: ….insert one-to-many.class here….

So the question: What’s the problem here? Is this even possible? Should Ijust give up on mapping generic entities?

Answer 1

Mapping-by-code generated this for me:

<class name="NHTest.Review`1[[NHTest.Person, NHTest, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]" table="Review">
  ...
  <many-to-one name="Subject" column="..." />
</class>
<class name="Person">
  ...
  <bag name="Reviews">
    <key column="..." />
    <one-to-many class="NHTest.Review`1[[NHTest.Person, NHTest, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]" />
  </bag>
</class>

So, try with fully-qualified names.