Elasticsearch .NET for C# (.NET): Complete Guide with Examples

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1. What It Is and Why It's Needed

\nElasticsearch .NET (NEST) is the official high-level client for working with the Elasticsearch search engine from applications in C# and other .NET platform languages. The library provides a strongly typed API that allows you to perform all operations with Elasticsearch: document indexing, search, aggregations, index and mapping management, using patterns familiar to .NET developers (LINQ, async methods, serialization via System.Text.Json or Newtonsoft.Json).\n

\nWhy is this library needed? Elasticsearch is a powerful distributed full-text search and real-time analytics system. If your C# application needs to perform complex searches on large volumes of data (logs, products, documents), process analytical queries (aggregations), or manage an Elasticsearch cluster programmatically, then NEST is the standard choice. It hides the low-level details of HTTP requests and JSON serialization, providing a fluent interface and strong typing.\n

\nThe library supports all versions of Elasticsearch starting from 6.x, and is also compatible with .NET Standard 2.0, allowing its use in projects on .NET Framework 4.6.1+, .NET Core 2.0+ and .NET 5/6/7/8/9. NEST is actively developed by Elastic and the community, has detailed documentation and a large number of examples.\n

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2. Installation

Installation is done via NuGet Package Manager. Use one of the following commands:

// Via .NET CLI\ndotnet add package NEST\n\n// Via Package Manager Console\nInstall-Package NEST\n\n// Or via NuGet UI: search for "NEST" and install the latest stable version\n

You can also install the low-level client Elasticsearch.Net, but NEST includes it as a dependency.

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3. Quick Start — Minimal Working Example

Create a .NET console application and add using directives:

using System;\nusing System.Threading.Tasks;\nusing Nest;\nusing static System.Console;\n\npublic class Program\n{\n    public static async Task Main(string[] args)\n    {\n        // 1. Connection setup\n        var settings = new ConnectionSettings(new Uri("http://localhost:9200"))\n            .DefaultIndex("my_index");\n        \n        var client = new ElasticClient(settings);\n\n        // 2. Data model definition\n        var document = new Product\n        {\n            Id = 1,\n            Name = "Laptop",\n            Description = "Powerful gaming laptop",\n            Price = 1500.99\n        };\n\n        // 3. Document indexing\n        var indexResponse = await client.IndexAsync(document, idx => idx.Index("products"));\n        if (indexResponse.IsValid)\n            WriteLine($"Document indexed: {indexResponse.Id}");\n\n        // 4. Document search\n        var searchResponse = await client.SearchAsync(s => s\n            .Index("products")\n            .Query(q => q\n                .Match(m => m\n                    .Field(f => f.Name)\n                    .Query("laptop")\n                )\n            )\n        );\n\n        foreach (var hit in searchResponse.Hits)\n        {\n            WriteLine($"Found: {hit.Source.Name} - {hit.Source.Price:C}");\n        }\n    }\n}\n\npublic class Product\n{\n    public int Id { get; set; }\n    public string Name { get; set; }\n    public string Description { get; set; }\n    public double Price { get; set; }\n}\n

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4. Main Methods/Functions/Classes

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4.1. `ElasticClient.IndexAsync`

Signature: Task<IndexResponse> IndexAsync<T>(T document, Func<IndexDescriptor<T>, IIndexRequest<T>> selector = null, CancellationToken ct = default)

What it does: In