Elastic.Mapping

Compile-time Elasticsearch mappings for .NET. Native AOT ready. Define your index mappings, analysis chains, and field metadata with C# attributes and get reflection-free generated code that works with System.Text.Json source generation out of the box.

Why?

Elasticsearch field names are strings. Typos are silent. Refactors break queries. Manual JSON mappings drift from your code.

Elastic.Mapping fixes this with a source generator that turns your POCOs into type-safe, pre-computed mapping infrastructure at build time -- zero reflection, zero runtime overhead, fully AOT compatible.

Quick Start

1. Define your domain types (clean POCOs)

public class Product
{
    [Keyword]
    public string Id { get; set; }

    [Text(Analyzer = "standard")]
    public string Name { get; set; }

    public double Price { get; set; }

    public bool InStock { get; set; }

    [Nested]
    public List<Category> Categories { get; set; }
}

2. Register them in a mapping context

[ElasticsearchMappingContext]
[Index<Product>(Name = "products")]
[DataStream<ApplicationLog>(Type = "logs", Dataset = "myapp", Namespace = "production")]
public static partial class MyContext;

3. Use generated field constants and metadata

// Type-safe field names -- rename the C# property, these update automatically
MyContext.Product.Fields.Name      // "name"
MyContext.Product.Fields.Price     // "price"
MyContext.Product.Fields.InStock   // "inStock"

// Index targets
MyContext.Product.IndexStrategy.WriteTarget   // "products"

// Data stream naming follows Elastic conventions
MyContext.ApplicationLog.IndexStrategy.DataStreamName  // "logs-myapp-production"

// Pre-built JSON for index creation
var json = MyContext.Product.Context.GetIndexJson();

// Change detection -- only update when mappings actually change
if (clusterHash != MyContext.Product.Hash) UpdateMappings();

System.Text.Json Integration

Elastic.Mapping is built around System.Text.Json. Link your STJ source-generated JsonSerializerContext and the mapping generator inherits your serialization configuration automatically -- one source of truth for both JSON serialization and Elasticsearch field names.

// Your STJ source-generated context
[JsonSourceGenerationOptions(
    PropertyNamingPolicy = JsonKnownNamingPolicy.CamelCase,
    UseStringEnumConverter = true,
    DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull)]
[JsonSerializable(typeof(Product))]
[JsonSerializable(typeof(Order))]
public partial class MyJsonContext : JsonSerializerContext;

// Link it to the mapping context
[ElasticsearchMappingContext(JsonContext = typeof(MyJsonContext))]
[Index<Product>(Name = "products")]
[Index<Order>(Name = "orders")]
public static partial class MyContext;

The generator reads [JsonSourceGenerationOptions] at compile time and applies:

Per-property [JsonPropertyName("custom_name")] and [JsonIgnore] attributes are always respected, with or without a linked context.

This means your Elasticsearch field names, your JSON wire format, and your C# properties all stay in sync -- at compile time, with no reflection.

Native AOT

Every feature in Elastic.Mapping is AOT compatible:

• No reflection at runtime -- all field names, mappings JSON, and type metadata are generated as constants at compile time
• No dynamic code generation -- source generators run during build, not at runtime
• Pre-computed JSON -- settings and mappings are embedded as string literals, ready to send to Elasticsearch
• STJ source generation -- link your JsonSerializerContext for a fully AOT serialization pipeline

Publish with dotnet publish -p:PublishAot=true and everything works.

Field Type Attributes

Control how properties map to Elasticsearch field types:

Properties without attributes are inferred from their CLR type (string -> keyword, int -> integer, DateTime -> date, etc.).

Custom Configuration with IConfigureElasticsearch<T>

Implement IConfigureElasticsearch<T> to configure analysis, mappings, and index settings for a document type. There are two ways to wire this up:

Option A: Dedicated configuration class

Create a separate class that implements the interface and reference it via Configuration = typeof(...):

public class ProductConfig : IConfigureElasticsearch<Product>
{
    public AnalysisBuilder ConfigureAnalysis(AnalysisBuilder analysis) => analysis
        .Analyzer("product_search", a => a.Custom()
            .Tokenizer(BuiltIn.Tokenizers.Standard)
            .Filters(BuiltIn.TokenFilters.Lowercase, "english_stemmer", "edge_ngram_3_8"))
        .TokenFilter("english_stemmer", f => f.Stemmer()
            .Language(BuiltIn.StemmerLanguages.English))
        .TokenFilter("edge_ngram_3_8", f => f.EdgeNGram()
            .MinGram(3).MaxGram(8));

    public MappingsBuilder<Product> ConfigureMappings(MappingsBuilder<Product> mappings) => mappings
        .Name(f => f.Analyzer("product_search")
            .MultiField("keyword", mf => mf.Keyword().IgnoreAbove(256)));

    public IReadOnlyDictionary<string, string> IndexSettings => new Dictionary<string, string>
    {
        ["index.default_pipeline"] = "product-enrichment"
    };
}

[ElasticsearchMappingContext]
[Index<Product>(Name = "products", Configuration = typeof(ProductConfig))]
public static partial class MyContext;

Option B: Self-configuring entity

If you prefer to keep configuration on the entity itself, implement the interface directly:

public class Product : IConfigureElasticsearch<Product>
{
    [Keyword]
    public string Id { get; set; }

    [Text(Analyzer = "product_search")]
    public string Name { get; set; }

    public double Price { get; set; }

    public AnalysisBuilder ConfigureAnalysis(AnalysisBuilder analysis) => analysis
        .Analyzer("product_search", a => a.Custom()
            .Tokenizer(BuiltIn.Tokenizers.Standard)
            .Filters(BuiltIn.TokenFilters.Lowercase));

    public MappingsBuilder<Product> ConfigureMappings(MappingsBuilder<Product> mappings) => mappings
        .Name(f => f.Analyzer("product_search")
            .MultiField("keyword", mf => mf.Keyword().IgnoreAbove(256)));
}

// No Configuration needed -- the generator detects the interface on the entity itself
[ElasticsearchMappingContext]
[Index<Product>(Name = "products")]
public static partial class MyContext;

All three interface members use default implementations, so you only need to override what you customize:

The generated ProductAnalysis class gives you type-safe constants for your custom components:

MyContext.Product.Analysis.Analyzers.ProductSearch     // "product_search"
MyContext.Product.Analysis.TokenFilters.EnglishStemmer  // "english_stemmer"

Dependency Injection

If your configuration class needs services (e.g. to read settings from IConfiguration), call RegisterServiceProvider before first access to mapping JSON:

// In your startup / Program.cs
services.AddSingleton<IConfigureElasticsearch<Product>, ProductConfig>();

var sp = services.BuildServiceProvider();
MyContext.RegisterServiceProvider(sp);

When no IServiceProvider is registered (or the service isn't found), the generator falls back to new ProductConfig() (parameterless constructor).

Index Strategies

Traditional Index

[Index<Product>(
    Name = "products",
    WriteAlias = "products-write",
    ReadAlias = "products-read",
    Shards = 3,
    RefreshInterval = "5s"
)]

Rolling Date Index

[Index<Order>(Name = "orders", DatePattern = "yyyy.MM")]
// Write target: orders-2025.02
// Search pattern: orders-*

Data Stream (logs, metrics, traces)

[DataStream<ApplicationLog>(Type = "logs", Dataset = "ecommerce.app", Namespace = "production")]
// Data stream: logs-ecommerce.app-production
// Search pattern: logs-ecommerce.app-*

Mappings Builder

The source generator creates extension methods on MappingsBuilder<T> for each property on your registered types. Customize mappings at the property level with full IntelliSense:

public MappingsBuilder<Product> ConfigureMappings(MappingsBuilder<Product> mappings) => mappings
    .Name(f => f.Analyzer("product_search"))
    .Price(f => f.DocValues(true))
    .AddRuntimeField("discount_pct", r => r.Double()
        .Script("emit((doc['price'].value - doc['sale_price'].value) / doc['price'].value * 100)"))
    .AddDynamicTemplate("labels_as_keyword", dt => dt
        .PathMatch("labels.*")
        .Mapping(m => m.Keyword()));

What Gets Generated

For each registered type, the source generator produces:

• Field constants -- MyContext.Product.Fields.Name (compile-time safe field names)
• Bidirectional field mapping -- PropertyToField / FieldToProperty dictionaries
• Index/search strategy -- write targets, search patterns, data stream names
• Settings + mappings JSON -- pre-computed, ready for index creation
• Content hashes -- detect when mappings change
• Analysis accessors -- type-safe constants for custom analyzers/filters
• Mappings builder extensions -- per-property fluent API on MappingsBuilder<T> for customization

All generated at compile time. Zero reflection at runtime. AOT compatible. Aligned with your System.Text.Json configuration.