ErrorOrX 2.6.0

ErrorOrX

Discriminated unions for .NET with source-generated ASP.NET Core Minimal API integration. Zero boilerplate, full AOT support.

Installation

dotnet add package ErrorOrX.Generators

Quick Start

// Program.cs
var app = WebApplication.CreateSlimBuilder(args).Build();
app.MapErrorOrEndpoints();
app.Run();

// TodoApi.cs
using ErrorOr;

public static class TodoApi
{
    [Get("/todos/{id}")]
    public static ErrorOr<Todo> GetById(int id, ITodoService svc)
        => svc.GetById(id).OrNotFound($"Todo {id} not found");

    [Post("/todos")]
    public static ErrorOr<Todo> Create(CreateTodoRequest req, ITodoService svc)
        => svc.Create(req);  // 201 Created

    [Delete("/todos/{id}")]
    public static ErrorOr<Deleted> Delete(int id, ITodoService svc)
        => svc.Delete(id) ? Result.Deleted : Error.NotFound();
}

Nullable-to-ErrorOr Extensions

Convert nullable values to ErrorOr<T> with fluent extensions:

// Auto-generates error code from type name (e.g., "Todo.NotFound")
return _todos.Find(t => t.Id == id).OrNotFound($"Todo {id} not found");
return user.OrUnauthorized("Invalid credentials");
return record.OrValidation("Record is invalid");

// Custom errors
return value.OrError(Error.Custom(422, "Custom.Code", "Custom message"));
return value.OrError(() => BuildExpensiveError());

Error Types

Error.Validation("User.InvalidEmail", "Email format is invalid")
Error.NotFound("User.NotFound", "User does not exist")
Error.Conflict("User.Duplicate", "Email already registered")
Error.Unauthorized("Auth.InvalidToken", "Token has expired")
Error.Forbidden("Auth.InsufficientRole", "Admin role required")
Error.Failure("Db.ConnectionFailed", "Database unavailable")
Error.Unexpected("Unknown", "An unexpected error occurred")
Error.Custom(422, "Validation.Complex", "Complex validation failed")

Fluent API

// Chain operations (railway-oriented programming)
var result = ValidateOrder(request)
    .Then(order => ProcessPayment(order))
    .Then(order => CreateShipment(order))
    .FailIf(order => order.Total <= 0, Error.Validation("Order.InvalidTotal", "Total must be positive"));

// Handle both cases
return result.Match(
    order => Ok(order),
    errors => BadRequest(errors.First().Description));

// Provide fallback on error
var user = GetUser(id).Else(errors => DefaultUser);

// Side effects
GetUser(id).Switch(
    user => Console.WriteLine($"Found: {user.Name}"),
    errors => Logger.LogError(errors.First().Description));

Result Markers

Result.Success   // 200 OK (no body)
Result.Created   // 201 Created (no body)
Result.Updated   // 204 No Content
Result.Deleted   // 204 No Content

Smart Parameter Binding

The generator automatically infers parameter sources:

[Post("/todos")]
public static ErrorOr<Todo> Create(
    CreateTodoRequest req,    // -> Body (POST + complex type)
    ITodoService svc)         // -> Service (interface)
    => svc.Create(req);

[Get("/todos/{id}")]
public static ErrorOr<Todo> GetById(
    int id,                   // -> Route (matches {id})
    ITodoService svc)         // -> Service
    => svc.GetById(id).OrNotFound();

Middleware Attributes

[Post("/admin")]
[Authorize("Admin")]
[EnableRateLimiting("fixed")]
[OutputCache(Duration = 60)]
public static ErrorOr<User> CreateAdmin(CreateUserRequest req) { }
// Generates: .RequireAuthorization("Admin").RequireRateLimiting("fixed").CacheOutput(...)

Native AOT

Fully compatible with PublishAot=true. The generator produces reflection-free code with automatic JSON serialization context generation.

<PropertyGroup>
  <PublishAot>true</PublishAot>
</PropertyGroup>

Documentation

• API Reference
• Parameter Binding
• Diagnostics
• Changelog

License

MIT