A simple hello world example which uses the low-level Elasticsearch .NET (low-level) client to index and retrieve some data. Also uses some new C# 9 language features.

HelloWorld.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net5.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Elasticsearch.Net" Version="7.10.0" />
  </ItemGroup>

</Project>

Program.cs

using System;
using System.Threading.Tasks;
using Elasticsearch.Net;

// defaults to localhost:9200
var client = new ElasticLowLevelClient();

var json = "{\"Id\":1,\"Title\":\"Pro .NET Memory Management\",\"ISBN\":\"978-1-4842-4026-7\"}";

// index a document from a JSON string, creating an index with auto-mapped properties
var indexResponse = await client.IndexAsync<StringResponse>("books", "1", PostData.String(json));

if (indexResponse.Success)
{
    await Task.Delay(10);

    // after a short delay, try to search for a book with a specific ISBN
    var searchResponse = await client.SearchAsync<StringResponse>("books", PostData.Serializable(new
    {
        query = new
        {
            match = new
            {
                isbn = new
                {
                    query = "978-1-4842-4026-7"
                }
            }
        }
    }));

    if (searchResponse.Success)
    {
        Console.WriteLine(searchResponse.Body);
        Console.WriteLine();
    }
}

var bookToIndex = new Book(2, "Pro .NET Benchmarking", "978-1-4842-4940-6");

// index another book, this time serializing an object
indexResponse = await client.IndexAsync<StringResponse>("books", bookToIndex.Id.ToString(), PostData.Serializable(bookToIndex));

if (indexResponse.Success)
{
    await Task.Delay(10);

    // after a short delay, get the book back by its ID
    var searchResponse = await client.GetAsync<DynamicResponse>("books", bookToIndex.Id.ToString());

    if (searchResponse.Success)
    {
        // access the title by path notation from the dynamic response
        Console.WriteLine($"Title: {searchResponse.Get<string>("_source.Title")}");
    }
}

// clean up by removing the index
await client.Indices.DeleteAsync<VoidResponse>("books");

// Using C# 9 record to define our book DTO
internal record Book(int Id, string Title, string ISBN);