The relationship could not be changed because one or more of the foreign-key properties is non-nullable

Question

I am getting this error when I GetById() on an entity and then set the collection of child entities to my new list which comes from the MVC view.

The

Answer 1

I used Mosh's solution, but it was not obvious to me how to implement the composition key correctly in code first.

So here is the solution:

public class Holiday
{
    [Key, Column(Order = 0), DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int HolidayId { get; set; }
    [Key, Column(Order = 1), ForeignKey("Location")]
    public LocationEnum LocationId { get; set; }

    public virtual Location Location { get; set; }

    public DateTime Date { get; set; }
    public string Name { get; set; }
}