使用CQRS处理中介管道中的错误/异常？

Question

我正在尝试按照Jimmy Bogard的这篇文章来实现一个中介管道,这样我就可以使用前/后请求处理程序来完成一些工作.从那篇文章的评论中,我来到这个github要点.我不太明白如何挂钩所有这些,所以这是我的第一次去.仅供参考 - 我正在使用Autofac进行DI和Web Api 2.遵循CQRS,这是一个查询.

public class GetAccountRequest : IAsyncRequest<GetAccountResponse>
{
    public int Id { get; set; }
}

//try using fluent validation
public class GetAccountRequestValidationHandler 
    : AbstractValidator<GetAccountRequest>, IAsyncPreRequestHandler<GetAccountRequest>
{
    public GetAccountRequestValidationHandler() {
        RuleFor(m => m.Id).GreaterThan(0).WithMessage("Please specify an id.");
    }

    public Task Handle(GetAccountRequest request) {
        Debug.WriteLine("GetAccountPreProcessor Handler");   
        return Task.FromResult(true);
    }
}

public class GetAccountResponse
{
    public int AccountId { get; set; }
    public string Name { get; set; }
    public string AccountNumber { get; set; }
    public string Nickname { get; set; }
    public string PhoneNumber { get; set; }
    public List<OrderAckNotification> OrderAckNotifications { get; set; }

    public class OrderAckNotification {
        public int Id { get; set; }
        public bool IsDefault { get; set; }
        public string Description { get; set; }
        public string Type { get; set; }
    }
}

GetAccountRequestHandler:

public class GetAccountRequestHandler 
    : IAsyncRequestHandler<GetAccountRequest, GetAccountResponse>
{
    private readonly IRedStripeDbContext _dbContext;

    public GetAccountRequestHandler(IRedStripeDbContext redStripeDbContext)
    {
        _dbContext = redStripeDbContext;
    }

    public async Task<GetAccountResponse> Handle(GetAccountRequest message)
    {
        //some mapping code here.. omitted for brevity
        Mapper.AssertConfigurationIsValid();

        return await _dbContext.Accounts.Where(a => a.AccountId == message.Id)
            .ProjectToSingleOrDefaultAsync<GetAccountResponse>();
    }

这是显示HttpGet的当前web api 2控制器.

[RoutePrefix("api/Accounts")]
public class AccountsController : ApiController
{
    private readonly IMediator _mediator;

    public AccountsController(IMediator mediator)
    {
        _mediator = mediator;
    }

    // GET: api/Accounts/2
    [Route("{id:int}")]
    [HttpGet]
    public async Task<IHttpActionResult> GetById([FromUri] GetAccountRequest request)
    {
        var model = await _mediator.SendAsync<GetAccountResponse>(request);

        return Ok(model);
    }
}

最后这里是依赖解析代码:

public void Configuration(IAppBuilder app)
{
    var config = new HttpConfiguration();

    ConfigureDependencyInjection(app, config);

    WebApiConfig.Register(config);
    app.UseWebApi(config);
}

private static void ConfigureDependencyInjection(IAppBuilder app, 
    HttpConfiguration config)
{
    var builder = new ContainerBuilder();
    builder.RegisterSource(new ContravariantRegistrationSource());
    builder.RegisterAssemblyTypes(typeof(IMediator).Assembly).AsImplementedInterfaces();

    builder.Register<SingleInstanceFactory>(ctx =>
    {
        var c = ctx.Resolve<IComponentContext>();
        return t => c.Resolve(t);
    });

    builder.Register<MultiInstanceFactory>(ctx =>
    {
        var c = ctx.Resolve<IComponentContext>();
        return t => (IEnumerable<object>)c.Resolve(
            typeof(IEnumerable<>).MakeGenericType(t));
    });

    //register all pre handlers
    builder.RegisterAssemblyTypes(Assembly.GetExecutingAssembly())
        .As(type => type.GetInterfaces()
            .Where(t => t.IsClosedTypeOf(typeof(IAsyncPreRequestHandler<>))));

    //register all post handlers
    builder.RegisterAssemblyTypes(Assembly.GetExecutingAssembly())
        .As(type => type.GetInterfaces()
            .Where(t => t.IsClosedTypeOf(typeof(IAsyncPostRequestHandler<,>))));


    //register all handlers
    builder.RegisterAssemblyTypes(Assembly.GetExecutingAssembly())
        .As(type => type.GetInterfaces()
            .Where(t => t.IsClosedTypeOf(typeof(IAsyncRequestHandler<,>)))
            .Select(t => new KeyedService("asyncRequestHandler", t)));

    //register pipeline decorator
    builder.RegisterGenericDecorator(typeof(AsyncMediatorPipeline<,>), 
        typeof(IAsyncRequestHandler<,>), "asyncRequestHandler");

    // Register Web API controller in executing assembly.
    builder.RegisterApiControllers(Assembly.GetExecutingAssembly()).InstancePerRequest();

    //register RedStripeDbContext
    builder.RegisterType<RedStripeDbContext>().As<IRedStripeDbContext>()
        .InstancePerRequest();

    builder.RegisterType<AutofacServiceLocator>().AsImplementedInterfaces();
    var container = builder.Build();

    config.DependencyResolver = new AutofacWebApiDependencyResolver(container);

    // This should be the first middleware added to the IAppBuilder.
    app.UseAutofacMiddleware(container);

    // Make sure the Autofac lifetime scope is passed to Web API.
    app.UseAutofacWebApi(config);
}

我正在进入GetAccountRequestValidationHandler.但是,当验证失败(传递了id为0)时,如何抛出异常或停止执行管道？如何返回.WithMessage？

Answer 1

我也一直在努力解决这个问题.似乎有两个/三个选项:

使用预处理程序......

1)您可以将错误加载到请求中,并让主处理程序在处理命令/查询之前检查错误

要么

2)让预处理程序抛出异常.对于这种做法,似乎存在一些分歧.一方面,感觉就像管理具有异常的控制流一样,但"专业"阵营认为客户端应该负责发送有效的命令.IE浏览器.在允许用户单击"创建帐户"之前,它可以发送ajax查询以确认用户名可用.在这种情况下,违反此规则的异常将归因于竞争条件.

将验证处理程序直接放入管道中.

我相信这更像是@jbogard所想的.我目前没有使用它,但我已经勾勒出了这可能是什么样子 - 那里可能有更好的例子,当然你要如何定义和处理事情可能会有所不同.它的要点是,当它成为管道的一部分时,验证运行器可以在没有调用主处理程序的情况下返回调用者.

public class AsyncValidationPipeline<TRequest, TResponse> : IAsyncRequestHandler<TRequest, TResponse>
    where TRequest : IAsyncRequest<TResponse>
{
    private IAsyncRequestHandler<TRequest, TResponse> _inner;
    private IValidator<TRequest>[] _validators;

    public AsyncValidationPipeline(IAsyncRequestHandler<TRequest, TResponse> inner,
        IValidator<TRequest>[] validators)
    {
        _inner = inner;
        _validators = validators;
    }
    public Task<TResponse> Handle(TRequest message)
    {
        List<string> errors = new List<string>();
        if (_validators != null && _validators.Any())
        {
            errors = _validators.Where(v => v.Fails(message))
                .Select(v => v.ErrorMessage);
        }

        if (errors.Any())
        {
            throw new ValidationException(errors);
        }
        return _inner.Handle(message);
    }
}

以下是使用AutoFac挂钩的代码:

            //register all pre handlers
            builder.RegisterAssemblyTypes(assembliesToScan)
                .AsClosedTypesOf(typeof(IAsyncPreRequestHandler<>));

            //register all post handlers
            builder.RegisterAssemblyTypes(assembliesToScan)
                .AsClosedTypesOf(typeof(IAsyncPostRequestHandler<,>));

            const string handlerKey = "async-service-handlers";
            const string pipelineKey = "async-service-pipelines";

            // Request/Response for Query

            builder.RegisterAssemblyTypes(assembliesToScan)
                .AsKeyedClosedTypesOf(typeof(IAsyncRequestHandler<,>), handlerKey)
                ;

            // Decorate All Services with our Pipeline
            //builder.RegisterGenericDecorator(typeof(MediatorPipeline<,>), typeof(IRequestHandler<,>), fromKey: "service-handlers", toKey: "pipeline-handlers");
           builder.RegisterGenericDecorator(typeof(AsyncMediatorPipeline<,>), typeof(IAsyncRequestHandler<,>), fromKey: handlerKey, toKey: pipelineKey);

            // Decorate All Pipelines with our Validator
           builder.RegisterGenericDecorator(typeof(AsyncValidationHandler<,>), typeof(IAsyncRequestHandler<,>), fromKey: pipelineKey);//, toKey: "async-validator-handlers");

           // Add as many pipelines as you want, but the to/from keys must be kept in order and unique

希望这可以帮助....