Setting a foreign key to null when using entity framework code first

I think the problem is that as far as the context is concerned, you haven’t actually changed anything.

You can use the lazy loading approach previously suggested by using virtual, but since you haven’t requested that the Employee be loaded yet, it’s still null. You could try this:

var forceLoad = project.Employee;
project.Employee = null; // Now EF knows something has changed
Context.SaveChanges();

Alternatively, explicitly include it in your original request:

var project = Context.Projects.Include(x => x.Employee).FirstOrDefault(x => x.ProjectId == projectId);
project.Employee = null;
Context.SaveChanges();

On a side note, FirstOrDefault will return null if no Project matches the given id. If you know the project exists, you can just use First. You could even use Single which will assert that there is only one such project. If you continue to use FirstOrDefault, I’d recommend checking for null before working with project.