Error when creating a one-to-many association at runtime with NHibernate?

I have situation where a few parts of my entity model is known only at runtime. In order to create queries in a simple way I'd like to add a simple one-to-many association on items referencing them before creating the SessionFactory.

I've looked at this post开发者_如何学JAVA in Ayende's blog and Extend/Modify NHibernate classes at runtime but I'm stuck at an error saying:

Unknown collection role: MySandbox.Parent.Children

What is a collection role and how do I instruct NHibernate to resolve it as if it was added in the hbm.xml?

My test:

using (var tx = this.session.BeginTransaction())
{
    parent = new Parent() { Name = "Parent 1" };
    this.session.Save(parent);
    tx.Commit(); //<- The exception is thrown here
}

My code for adding the association:

    // var cfg = <init nhibernate>

    PersistentClass cls = cfg.GetClassMapping("MySandbox.Parent");

    NHibernate.Mapping.Set value = new NHibernate.Mapping.Set(cls)
    {
        Role = cls.EntityName + ".Children",
        IsGeneric = true,
        GenericArguments = new Type[] { typeof(Child) }
    };

    NHibernate.Mapping.Property property = new NHibernate.Mapping.Property()
    {
        PropertyAccessorName = "noop",
        Value = value,
        Name = "Children",
        PersistentClass = cls
    };

    cls.AddProperty(property);

My classes:

public class Parent
{
    public virtual int ID { get; set; }
    public virtual string Name { get; set; }
}

public class Child
{
    public virtual int ID { get; set; }
    public virtual int ParentID { get; set; }
    public virtual string Name { get; set; }
}

The assocition mapping I'm trying to create at runtime:

<set name="Children" access="noop">
  <key column="ParentID" />
  <one-to-many class="MySandbox.Child, MySandbox"/>
</set>

It works perfect if I just create the association in the hbm.xml-file. I've also tried to compare a association created from xml with one created with the code above with no luck.

(Note: If I don't set the Role-property another exception of "Value cannot be null. Parameter name: key" is thrown.)

The error is because MySandbox.Child is not mapped. You need to map it (by creating a PersistentClass, etc) similar to how you did for the Parent class.