I have a relationship which would normally be described as one-to-one. It’s very similar to a Employee / EmployeeDetail relationship which you see used in many examples. My issue is that I’m working with legacy data, so the “child” part of the relationship, the EmployeeDetail, probably won’t exist.
I’m struggling to understand how to map this. I know if it wasn’t for the absent EmployeeDetails, this would be one-to-one. So I’m loathe to think about this in terms of another relationship type because as soon as the EmployeeDetail is available, it will be one-to-one again.
I’d appreciate any thoughts anyone out there might have.
One-to-one in NHibernate is a bit of a confusing beast. The one-to-one mapping assumes a shared primary key, which is not always the case. (For instance, you can’t use to map the relationship between Customer.HomeAddress and the Address table because HomeAddress would contain a FK to the Address table.) You may also run into problems with your scenario because EmployeeDetail may not always be present. An easier solution is to map it as a one-to-many and then picking up the first (and only) element in the returned collection. (I map it as an IList field and then have the unmapped T property deal with getting/setting the first element.)
James Kovacs