When using the grid in editmode popu with a editor template, was getting a Violation of a Foreign Key, debugging, I could see the fk value was being set, but it was blowing up in the DbSet.Add function. Thought it was the editor template configuration, but it wasn't. The table loaded in the drop downlist editor template was using a class called "InsurancePlan" - used to set the fk value - the grid was saving an "Insurance" object. The problem turns out because the InsurancePlan class included a virtual ICollection<Insurance>, but I had commented out the contructor, uncommenting the contructor resolved:
public InsurancePlan()
{
this.Insurances = new List<Insurance>();
}
