Hello: I am new to nhibernate and having been having issues modelling a simple relationship of parent child.
Parent table: parent_id [ Guid ]
Child table: child_id[guid], parent_id [ FK from Parent Table, Not null, Guid ]
Parent has a "list" of child objects [0...n]

The Parent Object references a HashedSet<Child>, however when I try to save

{"Cannot insert the value NULL into column 'parent_id', table 'tblChild'; column does not allow nulls. INSERT fails.\r\nThe statement has been terminated."}

I don't have any property in Child object referring the parent back, since the child shouldn't exist on its own.

Any pointers are much appreciated.

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<?xml version="1.0" encoding="utf-8"?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="mynamespace" assembly="mynamespace">
<class name="mynamespace.parent" table="tblParent">
<id name="ParentId column="parent_id">
<generator class="guid" />
</id>
<set name="Children" table="tblChild" lazy="true">
<key column="parent_id" not-null="true" />
<one-to-many class="Child" />
</set>
</class>
<class name="mynamespace.Child" table="tblChild">
<id name="ChildId" column="child_id">
<generator class="guid" />
</id>
<many-to-one name="ParentId" class="Parent" column="parent_id" not-null="true" />
</class>
</hibernate-mapping>
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Seems that you were intended to map a bidirectional association but you forget to specify the inverse attribute.