增加Mediat Pip特性，并用实例来做一个demo

Core/MAX.Framework/DependencyInjection/MediatRBehaviorServiceCollectionExtensions.cs

@@ -0,0 +1,71 @@
+using MAX.Framework.Mediation;
+// Adapted from ITIXO/MediatR.Extensions.AttributedBehaviors (MIT).
+// Copyright (c) 2021 ITIXO s.r.o. See ThirdPartyNotices/MediatR.Extensions.AttributedBehaviors.LICENSE.txt.
+using System.Reflection;
+using MAX.Core.Mediation;
+using MediatR;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+
+namespace MAX.Framework.DependencyInjection;
+
+public static class MediatRBehaviorServiceCollectionExtensions
+{
+    /// <summary>扫描命令特性，按声明行号注册闭合管道，适配 MediatR 9。</summary>
+    public static IServiceCollection AddMediatRAttributedBehaviors(this IServiceCollection services,
+        params Assembly[] assemblies)
+    {
+        ArgumentNullException.ThrowIfNull(services);
+        ArgumentNullException.ThrowIfNull(assemblies);
+        // 先完成全部校验，避免无效配置留下部分注册。
+        var registrations = new List<ServiceDescriptor>();
+        foreach (var request in assemblies.Distinct().SelectMany(a => a.DefinedTypes))
+        {
+            var attributes = request.GetCustomAttributes<MediatRBehaviorAttribute>(false)
+                .OrderBy(a => a.LineNumber).ToArray();
+            if (attributes.Length == 0) continue;
+            if (request.IsAbstract || request.ContainsGenericParameters)
+                throw new InvalidOperationException($"{request.FullName} 必须是具体的闭合请求类型。");
+            var responses = request.GetInterfaces()
+                .Where(i => i.IsGenericType && i.GetGenericTypeDefinition() == typeof(IRequest<>))
+                .Select(i => i.GetGenericArguments()[0]).Distinct().ToArray();
+            if (responses.Length != 1)
+                throw new InvalidOperationException($"{request.FullName} 必须实现唯一的 IRequest<TResponse>（无返回值使用 IRequest）。");
+            if (attributes.GroupBy(a => a.LineNumber).Any(g => g.Count() > 1))
+                throw new InvalidOperationException($"{request.FullName} 的管道特性必须独占一行，不能使用相同的行号。");
+            if (attributes.GroupBy(a => a.BehaviorType).Any(g => g.Count() > 1))
+                throw new InvalidOperationException($"{request.FullName} 重复声明了同一个管道。");
+
+            var serviceType = typeof(IPipelineBehavior<,>).MakeGenericType(request.AsType(), responses[0]);
+            foreach (var attribute in attributes)
+            {
+                var behavior = attribute.BehaviorType;
+                if (behavior.IsGenericTypeDefinition)
+                {
+                    if (behavior.GetGenericArguments().Length != 2)
+                        throw new InvalidOperationException($"开放泛型管道 {behavior} 必须具有 TRequest、TResponse 两个泛型参数。");
+                    try
+                    {
+                        behavior = behavior.MakeGenericType(request.AsType(), responses[0]);
+                    }
+                    catch (ArgumentException exception)
+                    {
+                        throw new InvalidOperationException($"管道 {behavior} 的泛型约束与请求 {request.FullName} 不匹配。", exception);
+                    }
+                }
+                if (!behavior.IsClass || behavior.IsAbstract || behavior.ContainsGenericParameters
+                    || !serviceType.IsAssignableFrom(behavior))
+                    throw new InvalidOperationException($"管道 {behavior.FullName} 必须是实现 {serviceType} 的具体闭合类型。");
+                registrations.Add(ServiceDescriptor.Transient(serviceType, behavior));
+            }
+        }
+        services.TryAddSingleton<UnitOfWorkExecutionContext>();
+        services.TryAddTransient<ServiceFactory>(provider => provider.GetRequiredService);
+        services.TryAddTransient<IMediator, Mediator>();
+        services.TryAddTransient<ISender>(provider => provider.GetRequiredService<IMediator>());
+        services.TryAddTransient<IPublisher>(provider => provider.GetRequiredService<IMediator>());
+        foreach (var registration in registrations)
+            services.TryAddEnumerable(registration);
+        return services;
+    }
+}

Core/MAX.Framework/DependencyInjection/ServiceCollectionExtensions.cs

@@ -64,6 +64,7 @@ namespace MAX.Framework.DependencyInjection
 			RunDebugStep("Plugin", "注册全部插件", () => RunPlugins(host, assemblies, instances));
 
 			RunDebugStep("Startup", "初始化并注册启动服务", () => RunStartups(host.Services, assemblies, instances));
+            RunDebugStep("MediatR", "按命令特性注册管道", () => host.Services.AddMediatRAttributedBehaviors(assemblies.ToArray()));