Integrating with Immediate.Handlers

Calling Validate at the top of every handler is repetitive and easy to forget. Immediate.Validations ships an Immediate.Handlers Behavior<,> that does it for you. Add it to the assembly-wide behavior pipeline:

using Immediate.Handlers.Shared;
using Immediate.Validations.Shared;

[assembly: Behaviors(
	typeof(ValidationBehavior<,>)
)]

ValidationBehavior<TRequest, TResponse> is constrained to where TRequest : IValidationTarget<TRequest>. Immediate.Handlers only inserts a behavior into a pipeline when its constraints are satisfied, so the behavior applies automatically to every handler whose request type declares IValidationTarget<T>, and is silently omitted for every handler whose request does not. There is nothing per-handler to configure.

[Handler]
public static partial class GetUser
{
	[Validate]
	public sealed partial record Query : IValidationTarget<Query>
	{
		[GreaterThan(0)]
		public required int Id { get; init; }
	}

	private static async ValueTask<User> HandleAsync(
		Query query,
		UsersService usersService,
		CancellationToken token
	) => await usersService.GetUserAsync(query.Id, token);
}

Sending a Query with Id of 0 never reaches HandleAsync; the behavior throws a ValidationException first.

Where it sits in the pipeline

Behaviors run outermost-first in the order they are listed. ValidationBehavior<,> calls ValidationException.ThrowIfInvalid(request) and only then invokes the next stage, so anything listed after it is skipped for an invalid request, and anything listed before it — logging, metrics, a transaction scope — still runs and observes the exception. Put it early if you want validation to be cheap, later if you want cross-cutting concerns to see invalid requests. See Handlers and the behavior pipeline.

Handler-level pipelines

A [Behaviors] attribute on a handler replaces the assembly list for that handler rather than adding to it. If you override the pipeline for a handler whose request is a validation target, include ValidationBehavior<,> explicitly:

[Handler]
[Behaviors(
	typeof(LoggingBehavior<,>),
	typeof(ValidationBehavior<,>)
)]
public static partial class GetUser
{
	// …
}

Handling the exception

The failure surfaces as a ValidationException thrown out of the handler. Turning that into an HTTP 400 with a field-keyed body is covered in Handling validation failures.