Fluent NHibernate - How to map the foreign key column as a property

Question

I am sure this is a straightforward question but consider the following: I have a reference between company and sector as follows:

public class Company {
    pub         


        

Answer 1

This is easily done with a formula property.

public class Company {
  public virtual Guid Id { get; set; }
  public virtual Guid? SectorId { get; set; }
  public virtual Sector Sector { get; set; }
}

public class CompanyMap : ClassMap {
  public CompanyMap() {
    Id(x => x.Id); // Maps to a column named "Id"
    References(x => x.Sector); // Maps to a column named "Sector_id", unless you change the NHibernate default mapping rules.
    Map(x => x.SectorId).Formula("[Sector_id]");
  }    
}

This should act exactly how you want. When the Company is new, SectorId will be null; when Company is fetched from the DB, SectorId will be populated with the given formula value. The SectorId is exposed as a property, which makes it really nice for dealing with web drop downs, etc. When you save, you'll still need to bind the "real" association. Assuming that SectorId was selected in a form...

using (var txn = session.BeginTransaction()) {
  // Set the FK reference.
  company.Sector = session.Load(company.SectorId);
  // Save the new record.
  session.Save(company);
  // Commit the transaction.
  txn.Commit();
}