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LeanCorpus.SourceGen

NuGet

LeanCorpus.SourceGen generates typed, reflection-free document maps, schemas and materialisers at build time.

Generate your first document map

Install the core package and generator:

dotnet add package LeanCorpus
dotnet add package LeanCorpus.SourceGen

Define a partial model:

using Rowles.LeanCorpus.Mapping.Attributes;

[LeanDocument]
public partial class Product
{
    [LeanString("id", Required = true)]
    public required string Id { get; init; }

    [LeanText("title")]
    public string? Title { get; init; }

    [LeanNumeric("price")]
    public double Price { get; init; }
}

Build the project. The generator emits ProductIndex with:

Generated member Use
Fields Typed descriptors for queries and sorting
ToDocument(Product) Converts the model into a LeanDocument
FromStoredDocument(StoredDocument) Materialises a stored result
CreateSchema() Creates an index schema from the attributes
Map Exposes the generated LeanDocumentMap<Product>
Important

Mapped models must be non-nested, non-generic partial classes or structs. Mapped properties need accessible instance getters and assignable setters or init accessors.

Index with the generated map

using Rowles.LeanCorpus.Index.Indexer;
using Rowles.LeanCorpus.Store;

using var directory = new MMapDirectory("./products");
using var writer = new IndexWriter(directory, new IndexWriterConfig
{
    Schema = ProductIndex.CreateSchema()
});

writer.AddDocument(ProductIndex.ToDocument(new Product
{
    Id = "p-1",
    Title = "Source-generated search",
    Price = 19.99
}));
writer.Commit();

Search with typed fields

using Rowles.LeanCorpus.Search.Searcher;

using var searcher = new IndexSearcher(directory);
var results = searcher.Search(
    ProductIndex.Fields.Title.CreateTermQuery("search"),
    topN: 10);

You can also use ProductIndex.AsQueryable(searcher) for the typed LINQ provider.

Materialise a result from stored fields when the mapped shape supports round-tripping:

using Rowles.LeanCorpus.Mapping;

foreach (var hit in results.ScoreDocs)
{
    var stored = StoredDocument.Create(searcher.GetStoredFields(hit.DocId), null);
    var product = ProductIndex.FromStoredDocument(stored);
    Console.WriteLine($"{product.Id}: {product.Title} {product.Price:C}");
}

Choose an attribute

Attribute Use
LeanText Analysed full text
LeanString Exact strings and identifiers
LeanNumeric Numeric and explicitly encoded temporal values
LeanVector Dense vectors with a declared dimension
LeanGeoPoint Geographic coordinates
LeanStored Stored-only strings or binary values
LeanIgnore Exclude a property

Supported shapes include:

Attribute CLR shape
LeanText, LeanString string, string[], IReadOnlyList<string>
LeanNumeric Integral and floating-point types, DateTimeOffset, DateOnly, TimeOnly, decimal
LeanVector float[] with a positive Dimension
LeanGeoPoint LeanGeoLocation
LeanStored string, byte[]

Temporal and decimal values need an explicit LeanNumericEncoding. DecimalAsString is stored-only and must keep Stored = true.

Diagnose generator errors

Generator diagnostics use the LCGEN prefix and appear during a normal build. Start with the first diagnostic, correct the model shape or attribute configuration, then rebuild.

Tip

Inspect generated output through the IDE or compiler-generated-files support when diagnosing a model. Do not copy generated source into the project or edit files under obj.

Native AOT

The generated map uses concrete code rather than runtime reflection. This makes typed mapping and field resolution suitable for trimming and Native AOT.

Next steps

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