Fluent NHibernate mapping IDictionary<string, class> in a smart way

Question

Given these classes:

using System.Collections.Generic;

namespace FluentMappingsQuestion
{
    public class Entity
    {
        public virtual int Id { get; set; }
        public virtual IDictionary<string, Property> Properties { get; set; }
    }

    public class Property
    {
        public virtual Entity OwningEntity { get; set; }
        public virtual string Name { get; set; }
        public virtual int Value { get; set; }
        public virtual decimal OtherValue { get; set; }
    }
}

How can I map them using NHibernate (preferably fluent flavor) so that doing this is possible:

[Test]
public void EntityPropertyMappingTest()
{
    using (var session = _factory.OpenSession())
    {
        var entity = new Entity();

        // (#1) I would *really* like to use this
        entity.Properties["foo"] = new Property { Value = 42, OtherValue = 42.0M };

        session.Save(entity);
        session.Flush();

        // (#2) I would like the entity below to "update itself"
        // on .Save or .Flush. I got it to work with .Load()
        Assert.AreEqual(42, entity.Properties["foo"].Value);
        Assert.AreEqual(42.0M, entity.Properties["foo"].OtherValue);
        Assert.AreEqual("foo", entity.Properties["foo"].Name);
        Assert.AreEqual(entity, entity.Properties["foo"].Owner);
    }
}

I have almost managed to do this with these mappings:

// class EntityMap : ClassMap<Entity>
public EntityMap()
{
    Id(x => x.Id);
    HasMany(x => x.Properties)
    .Cascade.AllDeleteOrphan()
    .KeyColumn("EntityId")
    .AsMap(x => x.Name);
}

// class PropertyMap : ClassMap<Property>
public PropertyMap()
{
    Id(x => x.Id);
    References(x => x.OwningEntity).Column("EntityId");
    Map(x => x.Name).Length(32);
    Map(x => x.Value);
{

The problems I have:

• If I make Entity.Properties .Inverse(), it starts breaking
• If I don't make it .Inverse() then NHibernate does: INSERT(Entity), INSERT(Property), UPDATE(Property) instead of just INSERT(Entity), INSERT(Property)
• If I make Property.Name .Not.Nullable(), it starts breaking
• If I don't make it .Not.Nullable(), I have a hole in my db schema

How should I change my mappings?

Answer 1

I worked around this by specifying this mapping:

HasMany<Property>(Reveal.Member<Entity>("InternalProperties"))
  .AsMap(p => p.Name)
  .Cascade.AllDeleteOrphan()
  .Inverse();

and creating two properties of type IDictionary<string, Property>: Properties and InternalProperties. The first one is a proxy dictionary over the second one, and deals with setting the OwningEntity and Name properties for the Property entries.