Question

the sample code on http://msdn.microsoft.com/en-US/data/jj591620#RequiredToRequired is it even correct? the code is asking for OfficeAssignment prop on the Instructor class. it will not resolve for obvious reasons. what is the correct way of having a one-to-one relationship on ef now?

// Configure the primary key for the OfficeAssignment
modelBuilder.Entity<OfficeAssignment>()
.HasKey(t => t.InstructorID);

modelBuilder.Entity<Instructor>()
.HasRequired(t => t.OfficeAssignment)
.WithRequiredPrincipal(t => t.Instructor);


public class OfficeAssignment
{
    // Specifying InstructorID as a primary
    [Key()]
     public Int32 InstructorID { get; set; }

    public string Location { get; set; }

    // When the Entity Framework sees Timestamp attribute
    // it configures ConcurrencyCheck and DatabaseGeneratedPattern=Computed.
    [Timestamp]
    public Byte[] Timestamp { get; set; }

    // Navigation property
    public virtual Instructor Instructor { get; set; }
}

public class Instructor
{
   public Instructor()
   {
        this.Courses = new List<Course>();
   }

    // Primary key
    public int InstructorID { get; set; }
    public string LastName { get; set; }
    public string FirstName { get; set; }
    public System.DateTime HireDate { get; set; }

    // Navigation properties
    public virtual ICollection<Course> Courses { get; private set; }
}

Answer 1

There is mistake around the Local/office nav property. A few deliberate renames to clarify
Perhaps this….

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace one2one
{
class Program
{
    static void Main(string[] args)
    {
        var context = new Demo();
        var instructor = new Instructor();
        instructor.FirstName = "Big";
        instructor.LastName = "Willi";
        context.Set<Instructor>().Add(instructor);

        var office = new OfficeAssignment();
        office.Location = "is this where the demo broke down ? See POCO ";
        office.InstructorUsingThisOffice = instructor;

        context.Set<OfficeAssignment>().Add(office);

        context.SaveChanges();
    }
}
public class OfficeAssignment
{
    // Specifying InstructorID as a primary
    public Int32 InstructorID { get; set; }
    public string Location { get; set; }

    // Navigation property
    public virtual Instructor InstructorUsingThisOffice { get; set; }
}

public class Instructor
{

    // Primary key
    public int InstructorID { get; set; }
    public string LastName { get; set; }
    public string FirstName { get; set; }
   //navigation
    //missing
    public virtual OfficeAssignment TheofficeToUse { get; set; }

}
public class Demo : DbContext
{


    DbSet<OfficeAssignment> officeAssignments { get; set; }
    DbSet<Instructor> Instructors { get; set; }
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        // Configure the primary key for the OfficeAssignment
        modelBuilder.Entity<OfficeAssignment>()
        .HasKey(t => t.InstructorID);

        modelBuilder.Entity<Instructor>()
                    .HasRequired(t => t.TheofficeToUse)
                    .WithRequiredPrincipal(d => d.InstructorUsingThisOffice);  //current entity is principal, the navigation back.
       // and we share the same key... MUST with EF 1:1 foreign key


    }
}
}