How can I enable automatic slicing on Elasticsearch operations like UpdateByQuery or Reindex using the Nest client?

I'm using the Nest client to programmatically execute requests against an Elasticsearch index. I need to use the UpdateByQuery API to update existing data in my index. To improve performance on large data sets, the recommended approach is to use slicing. In my case I'd like to use the automatic slicing feature documented here.

I've tested this out in the Kibana dev console and it works beautifully. I'm struggling on how to set this property in code through the Nest client interface. here's a code snippet:

var request = new Nest.UpdateByQueryRequest(indexModel.Name);
request.Conflicts = Elasticsearch.Net.Conflicts.Proceed;
request.Query = filterQuery;

// TODO Need to set slices to auto but the current client doesn't allow it and the server 
// rejects a value of 0
request.Slices = 0;

var elasticResult = await _elasticClient.UpdateByQueryAsync(request, cancellationToken);

The comments on that property indicate that it can be set to "auto", but it expects a long so that's not possible.

  // Summary:
        //     The number of slices this task should be divided into. Defaults to 1, meaning
        //     the task isn't sliced into subtasks. Can be set to `auto`.
 public long? Slices { get; set; }

Setting to 0 just throws an error on the server. Has anyone else tried doing this? Is there some other way to configure this behavior? Other APIs seem to have the same problem, like ReindexOnServerAsync.

Solution

This was a bug in the spec and an unfortunate consequence of generating this part of the client from the spec.

The spec has been fixed and the change will be reflected in a future version of the client. For now though, it can be set with the following

var request = new Nest.UpdateByQueryRequest(indexModel.Name);
request.Conflicts = Elasticsearch.Net.Conflicts.Proceed;
request.Query = filterQuery;

((IRequest)request).RequestParameters.SetQueryString("slices", "auto");
var elasticResult = await _elasticClient.UpdateByQueryAsync(request, cancellationToken);