inverse=true

nfung · **Joined:** Mon May 30, 2005 11:20 pm **Posts:** 66

Trying (and having trouble understanding) to understand "inverse" ...

ou may map a bidirectional one-to-many association by mapping a one-to-many association to the same table column(s) as a many-to-one association and declaring the many-valued end inverse="true".

...
...
...

<many-to-one name="Parent" column="parent_id" not-null="true"

(We also need to add the Parent property to the Child class.)

Now that the Child entity is managing the state of the link, we tell the collection not to update the link. We use the inverse attribute.

<set name="Children" inverse="true">
<key column="parent_id" />
<one-to-many class="Child" />
</set>

What's meant by "managing the state of the link"???

Reference:
http://nhibernate.sourceforge.net/nh-do ... ollections

martijnb · **Joined:** Sat May 14, 2005 8:40 am **Posts:** 130

nfung wrote:

What's meant by "managing the state of the link"???

That means that the Child is responsible for maintaining the relation between Parent and Child. Example:

Code:

// NHibernate looks at the Parent property for the relation
childObject.Parent = parentObject;

When you set inverse="false", the relation between Parent and Child is managed by the parent:

Code:

// NHibernate doesn't look at the Parent property of the Child, but looks in the Children collection of the Parent to establish the relation.
parentObject.Children.Add(childObject) ;

KPixel · **Posted:** Tue Aug 30, 2005 10:09 am

And it affects the order of the SQL commands executed...

nfung · **Joined:** Mon May 30, 2005 11:20 pm **Posts:** 66

Thanks first of all.... I have specified "inverse" = true in the parent object "zInventory":

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
   <class name="warehouse.to.zInventory, WarehouseLib" table="zInventory">
   
      <id name="Inv_ID" column="inv_id" type="Int32" unsaved-value="0" > 
         <generator class="identity" /> 
      </id> 
      
      ... bunch of properties...
      
      <set name="Swatches" inverse="true" cascade="all" table="inv_swatches" lazy="false">
         <key column="inv_id"/>
         <one-to-many class="warehouse.to.inv_swatches, WarehouseLib"/>
      </set>
      
      
   </class>
</hibernate-mapping>

For my child object "Swatch":

Code:

Public Class inv_swatches
...
             Public Property ParentInventoryMaster() As warehouse.to.zInventory
      ... getter and setter...
      End Property
... 
End Class

However, in my parent class, I have:

Code:

Public Class zInventory
 ... 
Public Property Swatches() As Collections.ISet
         ... getters and setters...
      End Property
 ...
End Class

Is this wrong then? What I did is:
(1). Get children from parent class
AND
(2). Get parent from child class

I have this feeling from what you said you can ONLY do...
(1) if you specified inverse=false
OR
(2) if you specified inverse=true

For your information, my child class mapping file:

Code:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
   <class name="warehouse.to.inv_swatches, WarehouseLib" table="inv_swatches">

      <id name="SwatchID" column="swatch_id" type="Int32" unsaved-value="0" >
         <generator class="identity" /> 
      </id>
      
      <many-to-one name="ParentInventoryMaster" column="inv_id" class="warehouse.to.zInventory, WarehouseLib" not-null="true" />
      
      ... other stuff ...
      
   </class>
</hibernate-mapping>

Is this the reason why I keep getting "Row not found" on updates/deletes (as noted in my other post... http://nhibernate.sourceforge.net/forum ... .php?t=644 )

Help!