Question

Working on a project where I have more or less carte blanche to modify the database schema and object model (nice position to be in. (c:) Suppose I have a trivial inheritance tree like:

class Parent
{
    public int ID { get; set; }
}

class Child : Parent
{
    // some fields
}

Is it better to have a database schema where the child ID and the parent ID are the same (e.g., parent primary key is IDENTITY(1,1), child primary key is assigned and is a NOT NULL foreign key to the parent table), or should the child table maintain its own primary key and keep its reference to the parent table in another field? What are the considerations to be made in this case? What are the pro’s and con’s of each approach? NHibernate supports both, right?

Answer 1

I would let the child have it’s own id. It’d be useless information but that detriment is far outweighed by the fact that it would be an easily recognizable 1-to-1 relationship rather than a “How the heck does this work?” relationship.

And yes, nHibernate can handle one-to-one relationships.