HelloWorld.csproj

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

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

  <ItemGroup>
    <PackageReference Include="Elasticsearch.Net" Version="7.10.1" />
  </ItemGroup>

</Project>

MyApp.cs

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

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 client.Indices.RefreshAsync<VoidResponse>("books");
    
    // search for a book with a specific ISBN
    var searchResponse = await client.SearchAsync<DynamicResponse>("books", PostData.Serializable(new
    {
        query = new
        {
            match = new
            {
                ISBN = new
                {
                    query = "978-1-4842-4026-7"
                }
            }
        }
    }));
    
    if (searchResponse.Success)
    {
        // access the title by path notation from the dynamic response
        Console.WriteLine($"Title: {searchResponse.Get<string>("hits.hits.0._source.Title")}");
        Console.WriteLine();
    }
}

// call the local function
await IndexAndRetrieveAsync();

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

// we can declare local functions which are called from our top-level program
async Task IndexAndRetrieveAsync()
{
    Book bookToIndex = new(2, "Pro .NET Benchmarking", "978-1-4842-4940-6");
    
    // index another book, this time serializing an object
    var indexResponse = await client.IndexAsync<StringResponse>("books", bookToIndex.Id.ToString(), PostData.Serializable(bookToIndex));
    
    if (indexResponse.Success)
    {
        // get the book back by its ID
        var searchResponse = await client.GetAsync<StringResponse>("books", bookToIndex.Id.ToString());
        if (searchResponse.Success)
        {
            Console.WriteLine($"Response body: {searchResponse.Body}");
        }
    }
}

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