mapping nhibernate parent/child relationship the 'other' way round

Question

using FluentNhibernate;

I am trying to persist a seemingly simple object model:

public class Product
{
    public int Id { get; set; }
    public string          


        

Answer 1

You are trying to map a one-to-one relationship as a one-to-many by mapping what would be the many side twice. That won't work. NHibernate is strict in its definition of one-to-one and requires that both sides have the same primary key, so that won't work either.

I've butted heads with this before and the best workaround I found is to model it as a standard on-to-many but only allow one item in the collection by encapsulating access to the it. In your case I would guess that Product would be the one side and Config the many.

Answer 2

I'm not sure if Config is used elsewhere but you could ignore ConfigId as its identity

public class Config
{
    public int Id { get; set; }
    public Product Product { get; set; }
    public string ConfigField1 { get; set; }
    public string ConfigField2 { get; set; }
}

public class ProductMap : ClassMap<Product>
{
    public class ProductMap()
    {
        HasOne(p => p.Config);
    }
}

public class ConfigMap : ClassMap<Config>
{
    public class ConfigMap()
    {
        Id(c => c.Id, "ProductId").GeneratedBy.Foreign("Product");

        References(c => c.Product, "ProductId");
        Map(c => ...);
    }
}

Answer 3

Another idea is to join and map as Component

public class ProductMap : ClassMap<Product>
{
    public class ProductMap()
    {
        Join("Config", join => 
        {
            join.KeyColumn("ProductId");
            join.Component(p => p.Config, c =>
            {
                c.Map(...);
            });
        }
    }
}

Disadvantage is that you can not query Config directly, you have to query through Product