public Person Add(Person person) {

            person.Id = _nextId;
            _peopleDictionary.TryAdd(person.Id, person);
            _nextId++;

            return person;
        }
        // POST /api/people
        public HttpResponseMessage PostPerson(Person person) {

            var createdPerson = _peopleCtx.Add(person);
            var response = Request.CreateResponse(HttpStatusCode.Created, createdPerson);
            response.Headers.Location = new Uri(
                Url.Link("DefaultHttpRoute", new { id = createdPerson.Id }));

            return response;
        }
        public bool TryUpdate(Person person) {

            Person oldPerson;
            if (_peopleDictionary.TryGetValue(person.Id, out oldPerson)) {

                return _peopleDictionary.TryUpdate(person.Id, person, oldPerson);
            }

            return false;
        }