public string GetReference(object context, object value)
        {
            PersonReference p = (PersonReference)value;

            _people[p.Id] = p;

            return(p.Id.ToString());
        }
        public bool IsReferenced(object context, object value)
        {
            PersonReference p = (PersonReference)value;

            return(_people.ContainsKey(p.Id));
        }