NHibernate/FluentNHibernate property bag

Question

Given a Vehicle class and a VehicleProperty class...

public class Vehicle
{
    public virtual int Id { get; protected set; }
    public virtual string Registration { get; set; }

    private List<VehicleProperty> _properties = new List<VehicleProperty>();
    public virtual IEnumerable<VehicleProperty> Properties
    {
        get { return _properties; }
        protected set{ _properties = new List<VehicleProperty>(value);}
    }

    public virtual void AddProperty(string name, string value)
    {
        _properties.Add(new VehicleProperty {Name = name, Value = value});
    }
}

public class VehicleProperty
{
    public virtual string Name { get; set; }
    public virtual string Value { get; set; }
}

How can I map the two classes so that the VehicleProperty table has a composite key of [VehicleId] and [Name]. Vehicle would be an aggregate root (VehicleProperty is not accessed outside of a Vehicle class).

I have tried everything that I can think of (I'm new to NHibernate so that's not much)

public class VehicleMap : ClassMap<Vehicle>
{
    public VehicleMap()
    {
        Id(x => x.Id);
        Map(x => x.Registration);
        HasMany(x => x.Properties)
            .Inverse()
            .Cascade.All();
    }
}

public class VehiclePropertyMap : ClassMap<VehicleProperty>
{
    public VehiclePropertyMap()
    {
        UseCompositeId()
            .WithKeyProperty(x => x.Name)
            .WithKeyReference(x => x.Vehicle, "Vehicle_Id");
        Map(x => x.Name);
        Map(x => x.Value);
    }
}

This mapping results in the below sql and a StaleStateException "Unexpected row count: 0; expected: 1" (I also don't really want to have a Vehicle property on the VehicleProperty)...

INSERT INTO "Vehicle" (Registration) VALUES (@p0); select last_insert_rowid(); @p0 = 'AA09CDE'
UPDATE "VehicleProperty" SET Name = @p0, Value = @p1 WHERE Name = @p2 AND Vehicle_Id = @p3; @p0 = 'Colour', @p1 = 'Black', @p2 = 'Colour', @p3 = ''

Answer 1

I agree entirely with Stefan's points, and although I can't attest to the correctness of his mapping, the literal translation into Fluent NHibernate is as follows:

public class VehicleMap : ClassMap<Vehicle>
{
  public VehicleMap()
  {
    Id(x => x.Id);
    Map(x => x.Registration);

    HasMany(x => x.Properties)
      .Component(c =>
      {
        c.Map(x => x.Name);
        c.Map(x => x.Value);
      })
      .Cascade.AllDeleteOrphan();
  }
}