Is it possible to avoid NHibernate.ObjectNotFoundException when there is a foreign key but the referenced row does not exist??

Question

I am using NHibernate to pull some data out of a legacy db, and I have found several cases where there is a foreign key, but the referenced row has been removed.

When I make my NHibernate mapping (using Fluent NHibernate like so:

References(d => d.Group)
    .WithColumns("groupId", "dataset")
    .SetAttribute("lazy", "true");

) I get an unitialized proxy for Group when loading the root object, followed by an ObjectNotFoundException when I attempt to use it.

If I disable lazy loading, I get an ObjectNotFoundException immediately when loading the root.

Therefore: Is there a way to have NHibernate make the Group null when loading the root? Or is it possible to check the unitialzed proxy somehow, to see if it will succeed in loading the row?

Answer 1

See Configuration.EntityNotFoundDelegate

Answer 2

I found the solution here - i needed to add

.SetAttribute("not-found", "ignore");

to the mapping.

Answer 3

Hi, have you verified that your referenced property is still loading lazily? In order for NHibernate to load references lazily, it needs to be sure that the reference is NOT NULL. When you set not-found="ignore", you are indirectly telling NHibernate that there is a possibility that the reference may not exist, hence preventing the NOT NULL constraint from being valid. In the case you've described above, you will not encounter an error but you may observe an eager call to the database to load your Group.