如何使用 MediatR 和 FluentValidation 实现通用 ValidationBehavion，以便 ValidationBehavion 仅在命令上触发

Question

我正在使用 CQRS 并分离命令和查询，我创建了自定义接口，因此我希望我的 ValidationBehavion 仅在继承 IRequest

的自定义 ICommand 上触发，而不是在所有 IRequest 请求上触发。

为了分离命令和查询，我创建了自定义界面： （作为响应值，我使用 ErrorOr 库。但我认为不值得研究它，只需记住命令和查询总是有响应）

public interface ICommand<TResponse> 
    : IRequest<ErrorOr<TResponse>>
{ 
}

public interface IQuery<TResponse> 
    : IRequest<ErrorOr<TResponse>>
{
}

public interface ICommandHandler<TCommand, TResponse> 
    : IRequestHandler<TCommand, ErrorOr<TResponse>>
    where TCommand : ICommand<TResponse>
{
}

public interface IQueryHandler<TQuery, TResponse>
    : IRequestHandler<TQuery, ErrorOr<TResponse>>
    where TQuery : IQuery<TResponse>
{
}

我知道一种标准方法，其中 IPipelineBehavior 会向任何请求者触发，然后我们检查该请求者是否有验证器：

public class ValidationBehavion<TRequest, TResponse>
    : IPipelineBehavior<TRequest, TResponse>
    where TRequest : IRequest<TResponse>
    where TResponse : IErrorOr

{
    private readonly IValidator<TRequest>? _validator;

    public ValidationBehavion(IValidator<TRequest>? validator = null)
    {
        _validator = validator;
    }

    public async Task<TResponse> Handle(TRequest request, 
    RequestHandlerDelegate<TResponse> next, 
    CancellationToken cancellationToken)
    {
        if(_validator is null)
        {
            return await next();
        }

        var validationResult = await _validator.ValidateAsync(request);

        if (validationResult.IsValid)
        {
            return await next();
        }

        var validationErrors = validationResult.Errors
                .ConvertAll(error =>
                Errors.Wands.NotValid(
                    error.PropertyName,
                    error.ErrorMessage));

        return (dynamic)validationErrors;
    }
}

由于命令和查询是分离的，我想我可以指定 ICommand

而不是 IRequest 并重做 ValidationBehavion，如下所示：

public class ValidationBehavion<TRequest, TResponse>
    : IPipelineBehavior<TRequest, ErrorOr<TResponse>>
    where TRequest : ICommand<TResponse>

{
    private readonly IValidator<TRequest> _validator;

    public ValidationBehavion(IValidator<TRequest> validator)
    {
        _validator = validator;
    }

    public async Task<ErrorOr<TResponse>> Handle(TRequest request, 
        RequestHandlerDelegate<ErrorOr<TResponse>> next, 
        CancellationToken cancellationToken)
    {
        var validationResult = await _validator.ValidateAsync(request);

        if (validationResult.IsValid)
        {
            return await next();
        }

        var validationErrors = validationResult.Errors
                .ConvertAll(error =>
                Errors.Wands.NotValid(
                    error.PropertyName,
                    error.ErrorMessage));

        return validationErrors;
    }
}

但是这个 IPipelineBehavior 根本不起作用，我不知道为什么。

Answer 1

您可能需要注册该行为。你的startup.cs应该看起来像这样：

public class Startup 
{
public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers();
    services.AddMediatR(typeof(Startup));
    services.AddValidatorsFromAssemblyContaining<Startup>();

    // Register pipeline behaviors
    services.AddTransient(typeof(IPipelineBehavior<,>), typeof(LoggingBehavior<,>));
    services.AddTransient(typeof(IPipelineBehavior<,>), typeof(AuthorizationBehavior<,>));
    services.AddTransient(typeof(IPipelineBehavior<,>), typeof(PerformanceBehavior<,>));
    services.AddTransient(typeof(IPipelineBehavior<,>), typeof(UnhandledExceptionBehavior<,>));

    // Register request pre-processors and post-processors
    services.AddTransient(typeof(IRequestPreProcessor<>), typeof(ValidationPreProcessor<>));
    services.AddTransient(typeof(IRequestPostProcessor<,>), typeof(LoggingPostProcessor<,>));
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }

    app.UseRouting();

    app.UseAuthorization();

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
    });
}
}

您在这里有完整的教程：

https://argosco.io/using-ipipelinebehavior-irequestpreprocessor-and-irequestpostprocessor-in-a-net-core-api/net/