// POST api/Todo
        public HttpResponseMessage PostTodoItem(TodoItemDto todoItemDto)
        {
            if (ModelState.IsValid)
            {
                TodoList todoList = db.TodoLists.Find(todoItemDto.TodoListId);
                if (todoList == null)
                {
                    return Request.CreateResponse(HttpStatusCode.NotFound);
                }

                if (todoList.UserId != User.Identity.Name)
                {
                    // Trying to add a record that does not belong to the user
                    return Request.CreateResponse(HttpStatusCode.Unauthorized);
                }

                TodoItem todoItem = todoItemDto.ToEntity();

                // Need to detach to avoid loop reference exception during JSON serialization
                db.Entry(todoList).State = EntityState.Detached;
                db.TodoItems.Add(todoItem);
                db.SaveChanges();
                todoItemDto.TodoItemId = todoItem.TodoItemId;

                HttpResponseMessage response = Request.CreateResponse(HttpStatusCode.Created, todoItemDto);
                response.Headers.Location = new Uri(Url.Link("DefaultApi", new { id = todoItemDto.TodoItemId }));
                return response;
            }
            else
            {
                return Request.CreateResponse(HttpStatusCode.BadRequest);
            }
        }
        // PUT api/Todo/5
        public HttpResponseMessage PutTodoItem(TodoItemDto todoItemDto)
        {
            if (ModelState.IsValid)
            {
                TodoItem todoItem = todoItemDto.ToEntity();
                TodoList todoList = db.TodoLists.Find(todoItem.TodoListId);
                if (todoList == null)
                {
                    return Request.CreateResponse(HttpStatusCode.NotFound);
                }

                if (todoList.UserId != User.Identity.Name)
                {
                    // Trying to modify a record that does not belong to the user
                    return Request.CreateResponse(HttpStatusCode.Unauthorized);
                }

                // Need to detach to avoid duplicate primary key exception when SaveChanges is called
                db.Entry(todoList).State = EntityState.Detached;
                db.Entry(todoItem).State = EntityState.Modified;

                try
                {
                    db.SaveChanges();
                }
                catch (DbUpdateConcurrencyException)
                {
                    return Request.CreateResponse(HttpStatusCode.InternalServerError);
                }

                return Request.CreateResponse(HttpStatusCode.OK);
            }
            else
            {
                return Request.CreateResponse(HttpStatusCode.BadRequest);
            }
        }