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peter.s.giles
 Post subject: Problems with self referencing objects and proxies
PostPosted: Tue Feb 20, 2007 7:23 pm 
Newbie

Joined: Tue Feb 20, 2007 5:41 pm
Posts: 5
Problem

I am using a three level object model where the second level subclass represents a bi-directional self referencing set of data.
The Parent ( Mother ) doesn't hyrate properly in this situation. While it has the values of the actual record all the member variables are null or default.

Code:
. . . . . . +-------+ . . . . .
. . . . . . |Entity | . . . . .
. . . . . . | . . . | . . . . .
. . . . . . +-------+ . . . . .
. . . . . . . .^. . . . . . . .
. . . . . . . .|. .+----+ . . .
. . . . . . +-------+ . | . . .
. . . . . . |Animal | . | . . .
. . . . . . | . . . |<--+ . . .
. . . . . . +-------+ . . . . .
. . . . . . . .^. . . . . . . .
. . . . . . . .|. . . . . . . .
. . . . +------+------+ . . . .
. . . . | . . . . . . | . . . .
. . . +---+ . . . . +---+ . . .
. . . |Cat| . . . . |Dog| . . .
. . . +---+ . . . . +---+ . . .
. . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . .


NHibernate version: 1.2.0 beta 3

Name and version of the database I am using: SQL 2005 SP1

Mapping documents:

Code:
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="Entity.Core.Entity,Entity.Core" table="Entity" lazy="false">
    <id name="Key" column="EntityId" type="Int32" unsaved-value="0">
      <generator class="native"/>
    </id>
    <property column="IsActive" type="Boolean" name="IsActive" not-null="true" />
    <joined-subclass name="Entity.Core.Animal,Entity.Core" table="Animal">
      <key column="EntityId"/>
      <property column="Name" type="String" name="Name" length="50" />
      <bag name="Children" inverse="true" lazy="false" >
        <key column="Mother" />
        <one-to-many class="Entity.Core.Animal,Entity.Core" />
      </bag>
      <many-to-one name="Mother" cascade="none" column="Mother" class="Entity.Core.Animal,Entity.Core" />
      <joined-subclass name="Entity.Core.Cat,Entity.Core" table="Cat">
        <key column="EntityId"/>
      </joined-subclass>
      <joined-subclass name="Entity.Core.Dog,Entity.Core" table="Dog">
        <key column="EntityId"/>
      </joined-subclass>
    </joined-subclass>
  </class>
</hibernate-mapping>


Code between sessionFactory.openSession() and session.close():

Code:

protected void Page_Load(object sender, EventArgs e)
{
   ISession session = NHibernateSessionManager.Instance.GetSession();

   ITransaction tx = session.BeginTransaction();

   IQuery query = session.CreateQuery("select a from Entity as a where a.Key = :id");
   query.SetCharacter("id", '7');
   foreach (Core.Entity entity in query.Enumerable())
   {
      // This casts just fine
      Animal animal = entity as Animal;
      // Animal happens to be of type Cat
      if (animal != null)
      {
         // Cat cast to Dog = null normally a *good* but I suspect for the wrong reasons so *bad*
         Dog dogParent = animal.Mother as Dog;
         // Cat cast to Cat = null *bad*
         Cat catParent = animal.Mother as Cat;
         // Cat cast to Dog = null *good*
         Dog dogCurrent = animal as Dog;
         // Cat cast to Cat = not null *good*
         Cat catCurrent = animal as Cat;
         // Dog cast to Dog = not null *good*
         Dog dogChild = animal.Children[0] as Dog;
         // Dog cast to Cat = null *good*
         Cat catChild = animal.Children[0] as Cat;
      }
   }

   tx.Commit();

   session.Close();
}
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peter.s.giles
 Post subject:
PostPosted: Tue Feb 20, 2007 11:22 pm 
Newbie

Joined: Tue Feb 20, 2007 5:41 pm
Posts: 5
On tinkering a bit more (I have a killer headache now) ... I have noticed that when I explicitly turn lazy loading off on all classes and only leave it on on the collection of children. everything hydrates as expected, meaning that I can cast Cat to Cats and Dogs to Dogs properly.

It is possible (In fact probable) that I don't understand the intent of the lazy attribute in the HBM config but I would have expected that the default behaviour would that lazy loading would be off. If it does default to off how was I confusing it.

Anyhow here is the new HBM. It works although I'll have to think about it some more before I fully understand why.

Code:
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="Entity.Core.Entity,Entity.Core" table="Entity" lazy="false">
    <id name="Key" column="EntityId" type="Int32" unsaved-value="0">
      <generator class="native"/>
    </id>
    <property column="IsActive" type="Boolean" name="IsActive" not-null="true" />
    <joined-subclass name="Entity.Core.Animal,Entity.Core" table="Animal" lazy="false">
      <key column="EntityId"/>
      <property column="Name" type="String" name="Name" length="50" />
      <bag name="Children" inverse="true" lazy="true" >
        <key column="Mother" />
        <one-to-many class="Entity.Core.Animal,Entity.Core" />
      </bag>
      <many-to-one name="Mother" cascade="none" column="Mother" class="Entity.Core.Animal,Entity.Core" />
      <joined-subclass name="Entity.Core.Cat,Entity.Core" table="Cat" lazy="false">
        <key column="EntityId"/>
      </joined-subclass>
      <joined-subclass name="Entity.Core.Dog,Entity.Core" table="Dog" lazy="false">
        <key column="EntityId"/>
      </joined-subclass>
    </joined-subclass>
  </class>
</hibernate-mapping>
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peter.s.giles
 Post subject:
PostPosted: Tue Feb 20, 2007 11:46 pm 
Newbie

Joined: Tue Feb 20, 2007 5:41 pm
Posts: 5
oh yeah I forgot the cast exception which you guys might find relevant

Unable to cast object of type 'CProxyTypeEntity_CoreAnimalCore_NHibernate_ProxyINHibernateProxy_System_Runtime_SerializationISerializable2' to type 'Entity.Core.Dog'.

sorry for being such a dunce :)
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sergey
 Post subject:
PostPosted: Wed Feb 21, 2007 2:36 am 
Contributor
Contributor

Joined: Wed May 11, 2005 4:59 pm
Posts: 1766
Location: Prague, Czech Republic
Read http://www.hibernate.org/hib_docs/nhibernate/html/performance.html#performance-proxies
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peter.s.giles
 Post subject:
PostPosted: Wed Feb 21, 2007 3:14 am 
Newbie

Joined: Tue Feb 20, 2007 5:41 pm
Posts: 5
yep...that explains why it behaves that way.

thanks sergey I appreciate your help.
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