CQRS 命令/查询装饰器

Posted 2023-02-23

【中文标题】CQRS 命令/查询装饰器

【英文标题】：CQRS Commands/Queries decorators

【发布时间】：2021-12-19 10:12:51

【问题描述】：

如何为IQueryHandler 和ICommandHandler 添加自定义装饰器？

我正在尝试使用 Autofac 和 MediatR 库在简单的控制台应用程序中实现 CQRS 模式。

该项目具有以下结构：

我想以这种方式处理命令和查询：

请求处理程序装饰器应用 命令/查询处理程序装饰器应用 命令/查询处理程序做某事 命令/查询处理程序装饰器完成 请求处理程序装饰器完成

主文件：

internal class Program

    static async Task Main(string[] args)
    
        var container = ConfigureCQRS();
        using var scope = container.BeginLifetimeScope();

        var mediatr = scope.Resolve<IMediator>();

        await mediatr.Send(new MyCommand("Command1"));
        await mediatr.Send(new MyQuery("Query1"));
    

    private static IContainer ConfigureCQRS()
    
        var builder = new ContainerBuilder();

        builder.RegisterModule(new MediatRModule(typeof(Program).Assembly));
        builder.RegisterGenericDecorator(typeof(LoggingRequestHandlerDecorator<,>), typeof(IRequestHandler<,>));
        builder.RegisterGenericDecorator(typeof(UnitOfWorkCommandHandlerDecorator<,>), typeof(ICommandHandler<,>));
        builder.RegisterGenericDecorator(typeof(DiagnosticQueryHandlerDecorator<,>), typeof(IQueryHandler<,>));

        return builder.Build();
    

MediatRModule.cs：

internal class MediatRModule : Autofac.Module

    private readonly Assembly[] assemblies;

    internal MediatRModule(params Assembly[] assemblies)
    
        this.assemblies = assemblies;
    

    protected override void Load(ContainerBuilder builder)
    
        builder.RegisterMediatR(assemblies);

        var openHandlerTypes = new[]
        
            typeof(IRequestHandler<,>),
            typeof(IRequestExceptionHandler<,,>),
            typeof(IRequestExceptionAction<,>),
            typeof(INotificationHandler<>),
        ;

        foreach (var openHandlerType in openHandlerTypes)
        
            builder.RegisterAssemblyTypes(this.assemblies)
             .AsClosedTypesOf(openHandlerType)
             .AsImplementedInterfaces();
        

        builder.RegisterGeneric(typeof(RequestPostProcessorBehavior<,>)).As(typeof(IPipelineBehavior<,>));
        builder.RegisterGeneric(typeof(RequestPreProcessorBehavior<,>)).As(typeof(IPipelineBehavior<,>));
        builder.RegisterGeneric(typeof(RequestExceptionActionProcessorBehavior<,>)).As(typeof(IPipelineBehavior<,>));
        builder.RegisterGeneric(typeof(RequestExceptionProcessorBehavior<,>)).As(typeof(IPipelineBehavior<,>));

        builder.Register<ServiceFactory>(outerContext =>
        
            var innerContext = outerContext.Resolve<IComponentContext>();

            return serviceType => innerContext.Resolve(serviceType);
        )
            .InstancePerLifetimeScope();
    

带有装饰器的典型命令：

internal record MyCommand(string Text) : CommandBase<string>;

internal class MyCommandHandler : ICommandHandler<MyCommand, string>

    public Task<string> Handle(MyCommand command, CancellationToken cancellationToken)
    
        Console.WriteLine($"Command result: command.Text");
        return Task.FromResult(command.Text);
    

典型的请求处理程序装饰器：

internal class LoggingRequestHandlerDecorator<TRequest, TResult> :
    IRequestHandler<TRequest, TResult>
    where TRequest : IRequest<TResult>

    private readonly IRequestHandler<TRequest, TResult> _decorated;

    public LoggingRequestHandlerDecorator(IRequestHandler<TRequest, TResult> decorated)
    
        this._decorated = decorated;
    

    public async Task<TResult> Handle(TRequest request, CancellationToken cancellationToken)
    
        Console.WriteLine("LoggingRequestHandlerDecorator start");
        var result = await _decorated.Handle(request, cancellationToken);
        Console.WriteLine("LoggingRequestHandlerDecorator end");
        return result;
    

典型的命令处理程序装饰器：

internal class UnitOfWorkCommandHandlerDecorator<TCommand, TResult> :
    ICommandHandler<TCommand, TResult>
    where TCommand : ICommand<TResult>

    private readonly ICommandHandler<TCommand, TResult> _decorated;

    public UnitOfWorkCommandHandlerDecorator(ICommandHandler<TCommand, TResult> decorated)
    
        _decorated = decorated;
    

    public async Task<TResult> Handle(TCommand command, CancellationToken cancellationToken)
    
        Console.WriteLine("UnitOfWorkCommandHandlerDecorator start");
        var result = await _decorated.Handle(command, cancellationToken);
        Console.WriteLine("UnitOfWorkCommandHandlerDecorator end");
        return result;
    

完整项目发布在github上：github.com/LeftTwixWand/CommandQueryDecorators

【参考方案1】：

好的，我已经解决了这个问题。 只需要在装饰器的构造函数中接受 IRequestHandler 即可。

【讨论】：

对于这些用例，您还可以使用行为，请参阅github.com/jbogard/MediatR/wiki/Behaviors

@GeorgMüller 感谢您的评论！我知道管道，但我在某些情况下需要使用装饰器，例如，测量查询速度，并且看起来，装饰器是正确的决定。