Validation

GenDI pattern: Use [Injectable] + [Inject] for regular application services. Concrete non-generic validation behaviors can also use [Injectable] because IPipelineRequestBehavior<,> / IPipelineNotificationBehavior<> already expose ServiceInjection. Only generic/open behavior implementations should be registered manually in builder.Services.

NetMediate does not include a built-in validation layer. Validation is a cross-cutting concern that you implement as a pipeline behavior.

DataAnnotations example

using System.ComponentModel.DataAnnotations;
using GenDI;
using Microsoft.Extensions.DependencyInjection;
using NetMediate;

public record CreateUserRequest(string Email);
public record UserDto(string Id, string Email);

[Injectable(ServiceLifetime.Singleton, Group = 10, Order = 1)]
public sealed class CreateUserDataAnnotationsBehavior : IPipelineRequestBehavior<CreateUserRequest, UserDto>
{
    public Task<UserDto> Handle(
        object? key,
        CreateUserRequest message,
        PipelineBehaviorDelegate<CreateUserRequest, Task<UserDto>> next,
        CancellationToken cancellationToken)
    {
        var context = new ValidationContext(message);
        var results = new List<ValidationResult>();

        if (!Validator.TryValidateObject(message, context, results, validateAllProperties: true))
            throw new MessageValidationException(results[0]);

        return next(key, message, cancellationToken);
    }
}

builder.Services.AddNetMediate();

FluentValidation example

using FluentValidation;
using GenDI;
using Microsoft.Extensions.DependencyInjection;
using NetMediate;

public record CreateUserRequest(string Email);
public record UserDto(string Id, string Email);

public sealed class CreateUserRequestValidator : AbstractValidator<CreateUserRequest>
{
    public CreateUserRequestValidator() => RuleFor(x => x.Email).NotEmpty().EmailAddress();
}

[Injectable(ServiceLifetime.Singleton, Group = 10, Order = 1)]
public sealed class CreateUserFluentValidationBehavior : IPipelineRequestBehavior<CreateUserRequest, UserDto>
{
    [Inject] public required IValidator<CreateUserRequest> Validator { get; init; }

    public async Task<UserDto> Handle(
        object? key,
        CreateUserRequest message,
        PipelineBehaviorDelegate<CreateUserRequest, Task<UserDto>> next,
        CancellationToken cancellationToken)
    {
        var result = await Validator.ValidateAsync(message, cancellationToken);
        if (!result.IsValid)
            throw new ValidationException(result.Errors);

        return await next(key, message, cancellationToken);
    }
}

builder.Services.AddValidatorsFromAssemblyContaining<CreateUserRequestValidator>();
builder.Services.AddNetMediate();