DKNet

Send write commands

Part of DKNet.SlimBus.Extensions. Mark a write with Fluents.Requests.INoResponse (no return value) or IWitResponse<TResponse> (returns a value), then implement its handler.

Use the console-project setup in the Quick Start, then replace Program.cs with this example:

using DKNet.SlimBus.Extensions;
using FluentResults;
using Microsoft.Extensions.DependencyInjection;
using SlimMessageBus;
using SlimMessageBus.Host;
using SlimMessageBus.Host.Memory;

var services = new ServiceCollection();
services.AddLogging();
services.AddSlimMessageBus(mbb => mbb
    .AddServicesFromAssembly(typeof(Program).Assembly)
    .AddChildBus("Memory", m => m.WithProviderMemory().AutoDeclareFrom(typeof(Program).Assembly)));

await using var provider = services.BuildServiceProvider();
var bus = provider.GetRequiredService<IMessageBus>();

var created = await bus.Send(new CreateProduct("Widget", 9.99m));
Console.WriteLine($"CreateProduct -> IsSuccess={created.IsSuccess}, Id={created.Value}");

var deactivated = await bus.Send(new DeactivateProduct(Guid.NewGuid()));
Console.WriteLine($"DeactivateProduct (unknown id) -> IsSuccess={deactivated.IsSuccess}");

public record CreateProduct(string Name, decimal Price) : Fluents.Requests.IWitResponse<Guid>;

internal sealed class CreateProductHandler : Fluents.Requests.IHandler<CreateProduct, Guid>
{
    public Task<IResult<Guid>> OnHandle(CreateProduct request, CancellationToken cancellationToken) =>
        Task.FromResult<IResult<Guid>>(Result.Ok(Guid.NewGuid())); // a real handler persists the new Product first
}

public record DeactivateProduct(Guid ProductId) : Fluents.Requests.INoResponse;

internal sealed class DeactivateProductHandler : Fluents.Requests.IHandler<DeactivateProduct>
{
    public Task<IResultBase> OnHandle(DeactivateProduct request, CancellationToken cancellationToken) =>
        Task.FromResult<IResultBase>(Result.Fail(new NotFoundError("Product not found")));
    // a real handler looks the product up first and only fails when it is missing
}

Run with dotnet run. Prints CreateProduct -> IsSuccess=True, Id=<guid> then DeactivateProduct (unknown id) -> IsSuccess=False.

Fluents.Requests.IHandler<TRequest> is IRequestHandler<TRequest, IResultBase> constrained to TRequest : INoResponse, so OnHandle returns Task<IResultBase>. Fluents.Requests.IHandler<TRequest, TResponse> returns Task<IResult<TResponse>>. A caller gets the same shape back from IMessageBus.Send(...). With auto-save registered, a successful write saves the DbContext for you — the handler never calls SaveChangesAsync.


NotFoundError is a FluentResults.Error subclass for “the thing you addressed doesn’t exist” — return it from Result.Fail so an API layer (see DKNet.AspCore.Extensions’ response mapping) can translate it to HTTP 404.

Fluents.Requests.IWithKey<TKey> is a small companion interface (TKey Id { get; set; }) for requests addressed by an identifier. DKNet.SlimBus.Generators puts it on the update and action requests it emits, so shared code can read the key generically.

🧱 Where it fits

A write request is the trigger auto-save keys off: only types implementing Fluents.Requests.INoResponse or IWitResponse<T> are ever saved for you. DKNet.AspCore.Extensions maps these same contracts to minimal-API endpoints (MapPost, MapPut, MapDelete, and the *ById forms for IWithKey<TKey> requests) and turns a failed IResultBase/IResult<T> into a ProblemDetails response.

⚠️ Gotchas & limits

• Fluents.Requests.IWitResponse<T> and Fluents.Queries.IWitResponse<T> are different interfaces with the same name in different nested classes — one wraps IResult<T>, the other returns T? directly. Import them explicitly enough to keep them apart.
• The handler never calls SaveChangesAsync when auto-save is registered; calling it yourself as well does no harm but is redundant.
• A raw SlimMessageBus IRequestHandler<,> implementation is not a write for auto-save purposes. Only Fluents.Requests.INoResponse / IWitResponse<T> are recognized — see Auto-save after a successful write.
• Keep handlers stateless. Don’t cache request-specific state on the instance.

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