private AtomEntry UpdateEntry(string url, AtomEntry entry)
        {
            Guard.ArgumentNotNull(entry, "entry");

            try
            {
                var eTag = entry.GetSDataHttpETag();
                var batchItem = new SDataBatchRequestItem
                                {
                                    Url = url,
                                    Method = HttpMethod.Put,
                                    Entry = entry,
                                    ETag = eTag
                                };

                if (BatchProcess.Instance.AddToBatch(batchItem))
                {
                    return null;
                }

                var operation = new RequestOperation(HttpMethod.Put, entry) {ETag = eTag};
                var response = ExecuteRequest(url, operation, MediaType.AtomEntry, MediaType.Xml);
                entry = (AtomEntry) response.Content;

                if (!string.IsNullOrEmpty(response.ETag))
                {
                    entry.SetSDataHttpETag(response.ETag);
                }

                return entry;
            }
            catch (Exception ex)
            {
                throw new SDataClientException(ex.Message, ex);
            }
        }
        /// <summary>
        /// Reads resource information from the data source based on the URL and the ETag of the specified entry.
        /// </summary>
        /// <param name="request"></param>
        /// <param name="entry"></param>
        /// <returns></returns>
        public virtual AtomEntry ReadEntry(SDataBaseRequest request, AtomEntry entry)
        {
            Guard.ArgumentNotNull(request, "request");

            try
            {
                var requestUrl = request.ToString();
                var eTag = entry != null ? entry.GetSDataHttpETag() : null;
                var batchItem = new SDataBatchRequestItem
                                {
                                    Url = requestUrl,
                                    Method = HttpMethod.Get,
                                    ETag = eTag
                                };

                if (BatchProcess.Instance.AddToBatch(batchItem))
                {
                    return null;
                }

                var operation = new RequestOperation(HttpMethod.Get) {ETag = eTag};
                var response = ExecuteRequest(requestUrl, operation, MediaType.AtomEntry, MediaType.Xml);
                entry = (AtomEntry) response.Content;

                if (!string.IsNullOrEmpty(response.ETag))
                {
                    entry.SetSDataHttpETag(response.ETag);
                }

                return entry;
            }
            catch (Exception ex)
            {
                throw new SDataClientException(ex.Message, ex);
            }
        }