NHibernate - map a property of a runtime-defined type

Question

Alright, so I need to create a couple of tables, which need to be almost identical except for one field.

My model would roughly look like this:

class HouseGeometryModel
{
   public virtual int Id { get; set; }
   public virtual string Name { get; set; }
   //More fields...

   public virtual HouseAttributes Attributes { get; set; }
}

class DungeonGeometryModel
{
   public virtual int Id { get; set; }
   public virtual string Name { get; set; }
   //More fields, all identical to HouseGeometryModel...

   public virtual DungeonAttributes Attributes { get; set; }
}

class FortressGeometryModel
{
   public virtual int Id { get; set; }
   public virtual string Name { get; set; }
   //More fields, all identical to HouseGeometryModel...

   public virtual FortressAttributes Attributes { get; set; }
}

//More models...

So, basically only the Attributes property differs between all the models here, so I thought there could be a way to unify everything into a single (generic?) class.

I could come up with two ways to implement this:

1. Make a generic class GeometryModel<TAttributes> which would look like:

   class GeometryModel<TAttributes>
   {
       public virtual int Id { get; set; }
       public virtual string Name { get; set; }
       //More fields...
   
       public virtual TAttributes Attributes { get; set; }
   }
   

   The problem with this is that I fail to specify a fluent mapping. The mapping should also become generic this way (to implement ClassMap<GeometryModel<TAttributes>>) and therefore it would be impossible to instantiate it with NHibernate.

2. Make the Attributes property dynamic. It doesn't work either because NHibernate treats dynamic properties as object when creating a ClassMap<>.

Is there any solution to this?

Answer 1

I ended up doing it generic way with a runtime ClassMap<> binding.

My model looks like this:

class GeometryModel<TAttributes>
{
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
    //More fields...

    public virtual TAttributes Attributes { get; set; }
}

My mappings look like this:

class GeometryModelMap<TAttributes> : ClassMap<GeometryModel<TAttributes>>
{
    public GeometryModelMap()
    {
        Id(t => t.Id).GeneratedBy.Increment();
        Map(t => t.Name);
        //More mappings...
        References(t => t.Attributes);
    }
}

I wrote the following extension method:

private static FluentMappingsContainer AddGenericMappings(this FluentMappingsContainer container, Type genericType, IEnumerable<Type> genericArgs)
{
    foreach (var arg in genericArgs)
    {
        var newType = genericType.MakeGenericType(arg);
        container.Add(newType);
    }
    return container;
}

And I use it like this:

private static ISessionFactory CreateSessionFactory(string path)
{
    return Fluently.Configure()
                   .Database(SQLiteConfiguration.Standard.UsingFile(path))
                   .Mappings(m => m.FluentMappings
                   .AddFromAssembly(Assembly.GetExecutingAssembly())
                   .AddGenericMappings(typeof(GeometryModelMap<>), new[] { typeof(HouseAttributes), typeof(DungeonAttributes), typeof(FortressAttributes) }  )
            )
            .ExposeConfiguration(config => BuildSchema(config, path))
            .BuildSessionFactory();
}