Scheme Generator

Scheme Generator builds default object graphs and JSON for any .NET type. Use it for unit tests, OpenAPI examples, and quick fixtures without hand-writing sample data.

Packages

Package	Description
SchemeGenerator	Core reflection-based generator
SchemeGenerator.SourceGenerators	Roslyn source generator for compile-time defaults
SchemeGenerator.Xunit	xUnit [Theory] data attributes
SchemeGenerator.AspNetCore	Swashbuckle schema example filter

All packages are version 10.1.0 and target net8.0, net9.0, and net10.0 (except the analyzer, which is a Roslyn component).

Requirements

• Consumers: .NET 8, 9, or 10
• Building from source: .NET 10 SDK (global.json)

Installation

Core package:

dotnet add package SchemeGenerator --version 10.1.0

With source generator:

dotnet add package SchemeGenerator --version 10.1.0
dotnet add package SchemeGenerator.SourceGenerators --version 10.1.0

Quick start

var generator = new SchemeGenerator();
var json = generator.GetDefaultJson(typeof(ComplexType));

// or with generics
var model = generator.GetDefault<ComplexType>();
var json2 = generator.GetDefaultJson<ComplexType>();

Dependency injection

builder.Services.AddSchemeGenerator(options =>
{
    options.CollectionItemCount = 2;
    options.PrimitiveMode = PrimitiveDefaultsMode.Sample;
});

// inject ISchemeGenerator

Options

Property	Default	Description
CollectionItemCount	1	Items in arrays and collections
MaxDepth	32	Max recursion depth (cycle safety)
PrimitiveMode	Zero	Zero = CLR defaults; Sample = realistic primitives
JsonSerializerOptions	null	Passed to GetDefaultJson

Attributes

Attribute	Target	Description
[SchemeIgnore]	Property	Skip property
[SchemeCount(n)]	Property	Override collection size
[SchemeValue(x)]	Property	Fixed value
[GenerateSchemeDefaults]	Type	Enable source generator (type must be partial)

Populate existing instances

var target = new SimpleType();
generator.Populate(target);

Source generator

Mark a partial type and reference the analyzer package:

[GenerateSchemeDefaults]
public partial class OrderDto
{
    public int Id { get; set; }
    public string Sku { get; set; } = string.Empty;
}

var order = OrderDto.OrderDtoSchemeDefaults.Create();
var json = OrderDto.OrderDtoSchemeDefaults.CreateJson();

Nested user types without [GenerateSchemeDefaults] fall back to the reflection-based SchemeGenerator at runtime.

xUnit integration

dotnet add package SchemeGenerator.Xunit --version 10.1.0

[Theory, AutoSchemeData<ComplexType>]
public void MyTest(ComplexType model) => Assert.NotNull(model);

[Theory, SchemeGeneratorData(typeof(SimpleType))]
public void OtherTest(SimpleType model) => Assert.NotNull(model);

ASP.NET Core / Swashbuckle

dotnet add package SchemeGenerator.AspNetCore --version 10.1.0

builder.Services.AddSchemeGenerator();

builder.Services.AddSwaggerGen(options =>
{
    options.AddSchemeGeneratorExamples();
});

Register SchemeGeneratorSchemaFilter via DI (Swashbuckle resolves it from the container when using AddSchemeGeneratorExamples).

Example output

public class SimpleType
{
    public int Number { get; set; }
    public string Text { get; set; }
}

public class ComplexType
{
    public List<int> Numbers { get; set; }
    public List<SimpleType> Objects { get; set; }
}

Default JSON (PrimitiveMode.Zero):

{
  "Numbers": [0],
  "Objects": [{ "Number": 0, "Text": "" }]
}

Benchmarks

See SchemeGenerator.Benchmarks:

dotnet run -c Release --project SchemeGenerator.Benchmarks

Compares reflection vs source-generated creation for the same DTO.

Building locally

dotnet restore
dotnet test -c Release
dotnet pack SchemeGenerator/SchemeGenerator.csproj -c Release
dotnet pack SchemeGenerator.SourceGenerators/SchemeGenerator.SourceGenerators.csproj -c Release
dotnet pack SchemeGenerator.Xunit/SchemeGenerator.Xunit.csproj -c Release
dotnet pack SchemeGenerator.AspNetCore/SchemeGenerator.AspNetCore.csproj -c Release

Contributing

See CONTRIBUTING.md. Release notes: CHANGELOG.md.

License

MIT — see LICENSE.