private Task <T> SingleOrDefaultAsync <T>(
IDocumentQuery <T> offerQuery,
CancellationToken cancellationToken)
{
if (offerQuery.HasMoreResults)
{
return(offerQuery.ExecuteNextAsync <T>(cancellationToken)
.ContinueWith(nextAsyncTask =>
{
DocumentFeedResponse <T> offerFeedResponse = nextAsyncTask.Result;
if (offerFeedResponse.Any())
{
return Task.FromResult(offerFeedResponse.Single());
}
return SingleOrDefaultAsync(offerQuery, cancellationToken);
})
.Unwrap());
}
return(Task.FromResult(default(T)));
}
//Helper to materialize Any IResourceFeed<T> from IResourceFeed<dynamic> as long as source
//conversion from dynamic to T.
//This method is invoked via expression as part of dynamic binding of cast operator.
public static DocumentFeedResponse <T> Convert <T>(DocumentFeedResponse <dynamic> dynamicFeed)
{
if (typeof(T) == typeof(object))
{
return((DocumentFeedResponse <T>)(object) dynamicFeed);
}
IList <T> result = new List <T>();
foreach (T item in dynamicFeed)
{
result.Add(item);
}
return(new DocumentFeedResponse <T>(
result,
dynamicFeed.Count,
dynamicFeed.Headers,
dynamicFeed.UseETagAsContinuation,
dynamicFeed.QueryMetrics,
dynamicFeed.RequestStatistics,
responseLengthBytes: dynamicFeed.ResponseLengthBytes));
}
