Delete from collection not working in Nhibernate

Question

Hi, I know there are many threads about this around, but I've been trying everything I could see for a while now but still no luck.

I have an Item object, which contains a collection of itemdocument. Using nhibernate to link to the database, I can easily add to my collection of itemdocument, update items in it, etc, but whatever I do, I cannot delete.

I load the item from the same session I try to delete it from. I even added the session as a property of the item object, and use that property to save it, just in case.

If I use a Session.Delete() on an itemdocument in the collection, and then I re-save the item object (without removing the itemdocument from the collection), it actually creates a new object, which is to be expected. So that tells me my Save are working.

I hope this all makes sense, I'm getting a bit frustrated and might not be as clear as I want...

See my mappings for the item object:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="namespace.Business.BusinessEntity">

  <class name="Item, namespace" table="[dbo].[Item]">

    <id name="ItemId" column="ItemId" type="Int32" unsaved-value="0">
      <generator class="identity" />
    </id>       

    <property name="ItemCode" column="ItemCode" type="String" length="50" />
    <property name="InternalDescription" column="InternalDescription" type="String" length="254" />
    <property name="IsEnabled" column="IsEnabled" type="Boolean" />
    <property name="Size" column="Size" type="String" length="50" />      

    <set name="Pictures" cascade="all-delete-orphan" inverse="true" >
      <key column="ItemId" not-null="true"/>
      <one-to-many class="ItemDocument" />
    </set>

  </class>
</hibernate-mapping>

Mapping for the Itemdocument object:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="namespace.Business.BusinessEntity">

  <class name="ItemDocument, namespace" table="[dbo].[ItemDocument]">

    <id name="ItemDocumentId" column="ItemDocumentId" type="Int32">
      <generator class="identity" />
    </id>       

    <property name="Order" column="[Order]" type="Int32"  />

    <many-to-one name="Item" class="Item" column="ItemId" not-null="true" />
    <many-to-one name="Document" class="Document" column="DocumentId"  cascade="save-update" not-null="true"/>

  </class>
</hibernate-mapping>

Code for the delete:

//This does nothing
item.Pictures.Remove(item.Pictures.ElementAt(0));
session.SaveOrUpdate(item);

//This neither
session.Delete(item.Pictures.ElementAt(0));
item.Pictures.Remove(item.Pictures.ElementAt(0));
session.SaveOrUpdate(item);

Answer 1

Have you tried to delete the collection item and then re-obtain the item? as in get the reference of the item you wish to delete, delete it, and then use hql to re-get the updated object?

Answer 2

Maybe it's just partial code, but there's no call to session.Flush(). Nothing is persisted to the database until Flush is called (for the default FlushMode of Auto). Try this:

item.Pictures.Remove(item.Pictures.ElementAt(0));
session.Flush();

You only need to call SaveOrUpdate if item is a transient object. Assuming that you already retrieved item using NHibernate then its persistent. Chapter 9 in the documentation has the details.

Edit: Pictures is the inverse side, so you have to set the reference to null on the "many" side of the collection:

var pictureToRemove = item.Pictures.ElementAt(0);
pictureToRemove.Item = null;
item.Pictures.Remove(pictureToRemove);
session.Flush();