Can I combine Retry and Fallback Polly resilience policies?

Question

I would like to perform a certain operation, and if it fails three times return null. Something like this in Polly would be perfect:

var results = await Policy<IList<Value>>
    .Handle<TaskCanceledException>()
    .RetryAsync<IList<Value>>(3)
    .FallbackAsync(null as IList<Value>)
    .ExecuteAsync(() => myRestfulCall());

This isn't possible as RetryAsync returns an AsyncRetryPolicy and there is no Fallback extension method defined on this type. Is there a Polly syntax to do this that doesn't require a try/catch block?

Glyptograph

Answer 1

Polly allows you to combine any policies flexibly via PolicyWrap: extensive documentation here.

The example you quote could be achieved something like:

var fallback = Policy<IList<Value>>
    .Handle<TaskCanceledException>()
    .FallbackAsync(null as IList<Value>);

var retry = Policy<IList<Value>>
    .Handle<TaskCanceledException>()
    .RetryAsync<IList<Value>>(3);

var results = await fallback.WrapAsync(retry)
    .ExecuteAsync(() => myRestfulCall());

Manuscript

I think you missed an await before the call to WrapAsync, but thank you that's exactly what I was missing. – Glyptograph