Hello, I have just started getting to gribs with NHibernate.

I have created a Parent / Child relationship, and I am able to successfully Add to the children collection so long as the parent exists.

Perhaps my understanding is wrong but I was under the impression it is possible to create a new parent object, then create a number of child objects, then save the whole lot to the database by just saving the Parent.
However when I try to add a child object, I get an error saying that a reference has not been set.

I have gone back to something simple, to get working first.

Simple XML Mapping
<class name="Parent" table="ARM_PARENT" discriminator-value="C">
<id name="Id" column="nId" type="Int32" unsaved-value="0">
generator class="identity"/>
</id>
<property name="Text" type="String" column="sText"/>

<bag name="Children" cascade="all-delete-orphan">
<key column="nParentId" />
<one-to-many class="Child" />
</bag>
</class>

<class name="Child" table="ARM_CHILD" discriminator-value="C">
<id name="Id" column="nId" type="Int32" unsaved-value="0">
<generator class="identity"/>
</id>
<property name="Text" type="String" column="sText"/>
<property name="ParentId" type="Int32" column="nParentId"/>
</class>

Simple code
Dim objNHibernate As New _NHibernate
Dim MyParent As New Parent
Dim MyChild As New Child

MyParent.Text = "Flub"
MyChild.Text = "xxxx"
MyParent.Children.Add(MyChild)
objNHibernate.Session.Save(MyParent)
objNHibernate.Session.Flush()

In my class Children is IList

I don't really understand the difference between using "bag" and "Set" in the mapping file either. :(

I would be grateful if you could help me get this concept straightened out. Thanks Stewart

hi Stewart,

a BAG is unsorted and may contain multiple instances of a row
a SET (like HashSet) has exactly one row for a certain ID

As Hibernate is not a managed container you have to tell the child
who his parents are:

this should work: