Question

Say I have:

public class Event {
   public int EventID { get; set; }
   ...
   public Sponsor Sponsor { get; set; }
}


public class Sponsor { get; set; }
   public int SponsorID { get; set; }
   ...
}

So an Event can have, but does not necessarily have, a Sponsor. I can create an Event, set a Sponsor and save it just fine.

What I cannot figure out how to make work is

Event event = context.Events.Find(id);
event.Sponsor = null;
context.SaveChanges();

The above doesn’t make a change to the sponsorid column in the database.

Answer 1

Try to make “Sponsor” a virtual property. Depending on your configuration, EF doesn’t know whether your have already loaded the Event.Sponsor property and if you haven’t it also doesn’t know that Sponsor = null is an actuall change. There are two kinds of proxys generated by the EF and depending on your POCOs EF hasn’t generated a self-tracking proxy for your Event-class (for example, the Navigation Property Sponsor isn’t virtual), so when it compares the snapshots of the previous Event entity, where “Sponsor” wasn’t loaded and the updated one, where “Sponser” was set to null, it assumes that you didn’t change it’s value.