Simple seeming Subclass Problem

Brett · **Posted:** Sun Sep 10, 2006 3:02 pm

Hi,

I have a Category class with a couple of collections of Properties associated with it; Read Only and Default. I've saved all these properties in one table and differentiated between them using a discriminator.

I think I should be able to define a couple of bags on Category and just specify which class they should come from and NHibernate would give me back my collections based on the discriminator.

However I have had to define where clauses on my bags. So yes it works; I'm not hugely worried about it, but it'd be really good to know if I've done my mapping incorrectly.

Thanks in advance,

Brett.

Hibernate version: 1.2 Beta

Mapping documents:

Code:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0" schema="dbo">
  <class name="Domain.DefaultProperty, Core" 
         table="nrp_CategoryDefault" discriminator-value="0" >
    <id name="ID" type="Int32" column="CategoryDefaultID" unsaved-value="0">
      <generator class="identity" />
    </id>
    <discriminator column="ReadOnly" type="Char" />
    <many-to-one name="ForCategory" column="CategoryID" class="Domain.Category, Core" />
    <many-to-one name="OfType" column="PropertyID" class="Domain.Property, Core" />
    <property name="Value" column="PropertyValue" />
    <subclass name="Domain.ReadOnlyDefaultProperty, Core" discriminator-value="1">
    </subclass>
  </class>
</hibernate-mapping> 

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0" schema="dbo">
  <class name="Domain.Category, Core" table="nrp_Category">
    <id name="ID" type="Int32" column="CategoryID" unsaved-value="0">
      <generator class="identity" />
    </id>
    <property name="Name" column="CategoryName" type="string" />
    <bag name="DefaultProperties" inverse="true" lazy="true" where="ReadOnly='0'">
      <key column="CategoryID" />
      <one-to-many class="Domain.DefaultProperty, Core" />
    </bag>
    <bag name="ReadOnlyProperties" inverse="true" lazy="true"  where="ReadOnly='1'">
      <key column="CategoryID" />
      <one-to-many class="Domain.ReadOnlyDefaultProperty, Core" />
    </bag>
  </class>
</hibernate-mapping>

Code between sessionFactory.openSession() and session.close():
Full stack trace of any exception that occurs: None
No exceptions.
Name and version of the database you are using: SQL Server 2000

The generated SQL (show_sql=true):

Debug level Hibernate log excerpt:

mnichols · **Joined:** Mon Aug 21, 2006 9:18 am **Posts:** 179

My first thot on this is that this is due to the polymorphism NHIbernate recognizes since ReadOnlyDefaultProperty *is* a DefaultProperty. You probably were ending up with ALL the entities inside the DefaultProperties collection, but getting only the ReadOnlyDefaultProperty entities inside your ReadOnlyProperties collection right?
Can you just define the 'class' element on a common supertype and then declare both DefaultProperty and ReadOnlyDefaultProperty as subclasses? I know this changes the Domain a bit, but that is the only I can think of around this.

MIKE

Brett · **Posted:** Wed Sep 13, 2006 10:35 am

OK - I think those are really good thoughts. I tried changing my mapping to use a base class and defined DefaultProperty as a subclass exactly the same as ReadOnlyDefaultProperty, only with a different discriminator.

When I remove my where clauses from the bags on category I get the following error:

2006-09-13 15:27:10,143 [TestRunnerThread] ERROR NHibernate.LazyInitializationException [(null)] <(null)> - cannot access loading collection
NHibernate.LazyInitializationException: cannot access loading collection

(Copied from my log4net log file which I guess I haven't configured quite right either).

I'm going to stick with my where clauses because they work.