一.介绍

   简单了解下开源项目 , , MediatR作者Jimmy Bogard :

Simple mediator implementation in .NETIn-process messaging with no dependencies.Supports request/response, commands, queries, notifications and events, synchronous and async with intelligent dispatching via C# generic variance. .NET中的简单中介实现 进程内没有依赖关系消息传递。支持以同步或异步的形式进行请求/响应，命令，查询，通知和事件的消息传递，并通过C#泛型支持消息的智能调度。

  MediatR实现Pipeline ,通过Autofac 注入Log, ,来实现管道里记录日志,管道里验证实体数据.

 

二.MediatR的使用

   1.安装NuGet包:

Install-Package MediatR.Extensions.Microsoft.DependencyInjectionFixed

Install-Package Autofac.Extensions.DependencyInjection

   2.修改Startup.cs文件

public IServiceProvider ConfigureServices(IServiceCollection services){      services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);      var container = new ContainerBuilder();      container.Populate(services);      container.RegisterModule(new MediatorModule());      return new AutofacServiceProvider(container.Build());}

   3.添加MediatorModule.cs文件

  添加 builder.RegisterGeneric(typeof(xxx<,>)).As(typeof(IPipelineBehavior<,>)); 按你添加的顺序执行管道

public class MediatorModule : Autofac.Module    {        protected override void Load(ContainerBuilder builder)        {            builder.RegisterAssemblyTypes(typeof(IMediator).GetTypeInfo().Assembly)                .AsImplementedInterfaces();                         // Register all the Command classes (they implement IRequestHandler) in assembly holding the Commands            builder.RegisterAssemblyTypes(typeof(CreateOrderCommand).GetTypeInfo().Assembly)                .AsClosedTypesOf(typeof(IRequestHandler<,>));//             Register the DomainEventHandler classes (they implement INotificationHandler<>) in assembly holding the Domain Events//            builder.RegisterAssemblyTypes(typeof(ValuesController.Pings).GetTypeInfo().Assembly)//                .AsClosedTypesOf(typeof(INotificationHandler<>));            // Register the Command's Validators (Validators based on FluentValidation library)            builder                .RegisterAssemblyTypes(typeof(CreateOrderCommandValidator).GetTypeInfo().Assembly)                .Where(t => t.IsClosedTypeOf(typeof(IValidator<>)))                .AsImplementedInterfaces();            builder.Register
     
      (context =>            {                var componentContext = context.Resolve
      
       ();                return t => { object o; return componentContext.TryResolve(t, out o) ? o : null; };            });            builder.RegisterGeneric(typeof(LoggingBehavior<,>)).As(typeof(IPipelineBehavior<,>));            builder.RegisterGeneric(typeof(ValidatorBehavior<,>)).As(typeof(IPipelineBehavior<,>));//            builder.RegisterGeneric(typeof(TransactionBehaviour<,>)).As(typeof(IPipelineBehavior<,>));        }    }
      
     

 

　4.添加LoggingBehavior.cs文件

public class LoggingBehavior
     
       : IPipelineBehavior
      
        {        private readonly ILogger
       
        
         > _logger;        public LoggingBehavior(ILogger
         
          
           > logger) => _logger = logger; public async Task
           
             Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate
            
              next) { _logger.LogInformation("----- Handling command {CommandName} ({@Command})", request.GetGenericTypeName(), request); var response = await next(); _logger.LogInformation("----- Command {CommandName} handled - response: {@Response}", request.GetGenericTypeName(), response); return response; } }
            
           
          
         
        
       
      
     

　5.添加ValidatorBehavior.cs文件

public class ValidatorBehavior
     
       : IPipelineBehavior
      
           {        private readonly ILogger
       
        
         > _logger;        private readonly IValidator
         
          [] _validators;        public ValidatorBehavior(IValidator
          
           [] validators, ILogger
           
            
             > logger) { _validators = validators; _logger = logger; } public async Task
             
               Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate
              
                next) { var typeName = request.GetGenericTypeName(); _logger.LogInformation("----- Validating command {CommandType}", typeName); var failures = _validators .Select(v => v.Validate(request)) .SelectMany(result => result.Errors) .Where(error => error != null) .ToList(); if (failures.Any()) { _logger.LogWarning("Validation errors - {CommandType} - Command: {@Command} - Errors: {@ValidationErrors}", typeName, request, failures); throw new OrderingDomainException( $"Command Validation Errors for type {typeof(TRequest).Name}", new ValidationException("Validation exception", failures)); } return await next(); } }
              
             
            
           
          
         
        
       
      
     

  6.添加CreateOrderCommandValidator.cs

public class CreateOrderCommandValidator : AbstractValidator
     
          {        public CreateOrderCommandValidator()        {            RuleFor(command => command.City).NotEmpty();            RuleFor(command => command.Street).NotEmpty();            RuleFor(command => command.State).NotEmpty();            RuleFor(command => command.Country).NotEmpty();            RuleFor(command => command.ZipCode).NotEmpty();            RuleFor(command => command.CardNumber).NotEmpty().Length(12, 19);             RuleFor(command => command.CardHolderName).NotEmpty();            RuleFor(command => command.CardExpiration).NotEmpty().Must(BeValidExpirationDate).WithMessage("Please specify a valid card expiration date");             RuleFor(command => command.CardSecurityNumber).NotEmpty().Length(3);             RuleFor(command => command.CardTypeId).NotEmpty();            RuleFor(command => command.OrderItems).Must(ContainOrderItems).WithMessage("No order items found");         }        private bool BeValidExpirationDate(DateTime dateTime)        {            return dateTime >= DateTime.UtcNow;        }        private bool ContainOrderItems(IEnumerable
      
        orderItems)        {            return orderItems.Any();        }    }