public async Task <IHttpActionResult> AddFriend(int userID, int friendID)
        {
            if (!ModelState.IsValid)
            {
                return(BadRequest(ModelState));
            }

            var user = await db.Users.FirstOrDefaultAsync((u) => u.UserID == userID);

            if (user == null)
            {
                return(BadRequest());
            }

            var friend = await db.Users.FirstOrDefaultAsync((u) => u.UserID == friendID);

            if (friend == null)
            {
                return(BadRequest());
            }

            await db.AddAFriend(userID, friendID);

            return(Ok());
        }