Question

Background: I am connecting to a legacy Database that has two entities:

Order (Id, Date, ...)    

ForwardOrder(OrderId)

… as you can see ForwardOrder could be just a property of an Order

Requirements: Try to reflect ForwardOrder as a Boolean property of Order class in .NET. Connect to the database with NHibernate.

The problem: I tried implementing IUserType but no luck – column doesn’t exist error.

The mapping is Map(x=>x.IsForwardOrder).CustomType<ForwardOrderType>();

Adding a Formula does make it load properly, but the IUserType setter is never used.

Question: Can it be done? Can an object’s existence in a separate table be a flag on my Entity? I know that I can just map a related object but I would rather to avoid that.

Answer 1

The way to do this is set up the ForwardOrder as a protected property on the code level and treat it like a lazy component. Then you can actually leave IsForwardOrder out of your NHibernate mapping completely and just do something like:

  public bool IsForwardOrder { get { return ReferenceEquals(this.ForwardOrder,null); } }

You could use polymorphism as well, but it seems like overkill for a boolean. This approach would entail creating a subclass that has the ForwardOrder property and defining a table-per-subclass join to the ForwardOrder table. You would still need to define a boolean property like

  public virtual bool IsForwardOrder { get { return false; } }

on the base class

  public override bool IsForwardOrder { get { return true; } }

on the joined subclass.

Alternatively, with this approach, you could use an extension method such as

 public static bool IsForwardOrder(this Order order) { return order is ForwardOrder; }

(assuming the base class is Order and the subclass is ForwardOrder)