public IHttpActionResult Post(File file)
 {
     file.FileId = _files.Count + 1;
     file.ModifiedDates.Add(new DateTime(2014, 12, 24, 9, 2, 3, DateTimeKind.Utc));
     _files.Add(file);
     return Created(file);
 }
        public IHttpActionResult Put(int key, File file)
        {
            if (key != file.FileId)
            {
                return BadRequest("The FileId of file is not matched with the key");
            }

            File original = _files.FirstOrDefault(c => c.FileId == key);
            _files.Remove(original);
            _files.Add(file);
            return Updated(file);
        }