BuildingBlocks.Mediator 1.0.0

BuildingBlocks.Mediator

CQRS-first Send + ordered pipeline mediator for .NET — ICommand / IQuery, ISender, host behaviors, optional telemetry, and startup handler validation.

Disclaimer: BuildingBlocks.Mediator is not designed to replace other mediator or messaging packages. It is a focused CQRS Send + pipeline building block for developers who want manual control over design patterns — registration, pipeline order, validation, telemetry, and host composition — rather than a batteries-included framework.

Requirements

• .NET 10 (net10.0) — v1 ships this TFM only (no multi-targeting)

Install

dotnet add package BuildingBlocks.Mediator

60-second quick start

services.AddMediator(cfg =>
{
    cfg.RegisterServicesFromAssemblyContaining<CreateOrderHandler>();
    cfg.AddOpenBehavior(typeof(ValidationBehavior<,>), order: 0);
    cfg.UseTelemetry();
    cfg.ValidateOnStartup = true;
});

public sealed record CreateOrder(string Product, int Qty) : ICommand<OrderId>;
public sealed class CreateOrderHandler : ICommandHandler<CreateOrder, OrderId>
{
    public Task<OrderId> Handle(CreateOrder command, CancellationToken ct)
        => Task.FromResult(new OrderId(Guid.NewGuid()));
}

// Prefer ISender at call sites
await sender.Send(new CreateOrder("SKU-1", 2), ct);

Features

• CQRS markers: ICommand / ICommand<T> / IQuery<T> (no non-generic IQuery)
• Void commands via ICommand : ICommand<Unit> (pipeline on the real type)
• Ordered open/closed pipeline behaviors (AddOpenBehavior + optional order)
• CommandPipelineBehavior / QueryPipelineBehavior filter bases
• UseTelemetry — optional ActivitySource enrichment around Send (wraps pipeline + handler; not a behavior)
• ValidateOnStartup — missing/duplicate handler checks at registration
• HandlerLifetime — configure discovered handler lifetime (default Transient)
• Exact-one handler resolution at Send (clear errors for missing/ambiguous handlers)
• Open-generic handlers — scanned and closed on demand
• Built-in assembly scanner — no Scrutor dependency

What it is not (v1)

• No Publish / INotification
• No streaming (CreateStream)
• No exception handlers that replace results (faults rethrow)
• No built-in FluentValidation or metrics (host AddOpenBehavior)
• Not fully Native AOT (runtime MakeGenericType wrappers)
• Open-generic handlers always resolve as Transient (ignore HandlerLifetime)

Docs

• Getting started
• Pipeline behaviors
• Cookbook
• v1.0 test matrix
• CHANGELOG

Demo host: FeatureFusion in the same repository.

License

MIT — Copyright (c) 2026 Mohammad Hasan Hosseini