https://stackoverflow.com/questions/44509884/unable-to-use-filter-path-with-nest-elasticsearch-5-0

filter-path.cs

void Main()
{
    var pool = new SingleNodeConnectionPool(new Uri("http://localhost:9200"));
    var defaultIndex = "default-index";
    var connectionSettings = new ConnectionSettings(pool)
        .DefaultIndex(defaultIndex)
        .PrettyJson()
        .DisableDirectStreaming()
        .OnRequestCompleted(response =>
            {
                if (response.RequestBodyInBytes != null)
                {
                    Console.WriteLine(
                        $"{response.HttpMethod} {response.Uri} \n" +
                        $"{Encoding.UTF8.GetString(response.RequestBodyInBytes)}");
                }
                else
                {
                    Console.WriteLine($"{response.HttpMethod} {response.Uri}");
                }

                Console.WriteLine();

                if (response.ResponseBodyInBytes != null)
                {
                    Console.WriteLine($"Status: {response.HttpStatusCode}\n" +
                             $"{Encoding.UTF8.GetString(response.ResponseBodyInBytes)}\n" +
                             $"{new string('-', 30)}\n");
                }
                else
                {
                    Console.WriteLine($"Status: {response.HttpStatusCode}\n" +
                             $"{new string('-', 30)}\n");
                }
            });

    var client = new ElasticClient(connectionSettings);

    if (client.IndexExists(defaultIndex).Exists)
        client.DeleteIndex(defaultIndex);
        
    client.CreateIndex(defaultIndex, c => c
        .Mappings(m => m
            .Map<Message>(mm => mm
                .AutoMap()
            )
        )
    );

    client.IndexMany(new[] {
        new Message { Content = "This is a test message" },
        new Message { Content = "Another one" },
        new Message { Content = "Yet another one" }
    });
    
    client.Refresh(defaultIndex);

    var searchResponse = client.Search<Message>(s => s
        .FilterPath("hits.hits._source")
        .Index(defaultIndex)
        .AllTypes()
        .Query(q => q
            .MatchAll()
        )
    );
}

public class Message
{
    public string Content { get; set; }
}