增加Mediat Pip特性，并用实例来做一个demo

Core/MAX.Core/Mediation/IValidatableRequest.cs

@@ -0,0 +1,7 @@
+namespace MAX.Core.Mediation;
+
+/// <summary>提供请求自身的参数校验；不合法时抛出 ValidationException。</summary>
+public interface IValidatableRequest
+{
+    void Validate();
+}

Core/MAX.Core/Mediation/MediatRBehaviorAttribute.cs

@@ -0,0 +1,13 @@
+// Adapted from ITIXO/MediatR.Extensions.AttributedBehaviors (MIT).
+// Copyright (c) 2021 ITIXO s.r.o. See ThirdPartyNotices/MediatR.Extensions.AttributedBehaviors.LICENSE.txt.
+using System.Runtime.CompilerServices;
+
+namespace MAX.Core.Mediation;
+
+/// <summary>声明命令管道。每个特性独占一行，按源码行号从上到下执行。</summary>
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct, AllowMultiple = true, Inherited = false)]
+public sealed class MediatRBehaviorAttribute(Type behaviorType, [CallerLineNumber] int lineNumber = 0) : Attribute
+{
+    public Type BehaviorType { get; } = behaviorType ?? throw new ArgumentNullException(nameof(behaviorType));
+    public int LineNumber { get; } = lineNumber;
+}

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()));
 
 
 

Core/MAX.Framework/Mediation/TransactionBehavior.cs

@@ -0,0 +1,26 @@
+using FreeSql;
+using MediatR;
+
+namespace MAX.Framework.Mediation;
+
+/// <summary>为通过特性选择的命令管理事务；所有读写使用执行上下文中的 ORM。</summary>
+public sealed class TransactionBehavior<TRequest, TResponse>(
+    IFreeSql freeSql, UnitOfWorkExecutionContext context) : IPipelineBehavior<TRequest, TResponse>
+    where TRequest : IRequest<TResponse>
+{
+    public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken,
+        RequestHandlerDelegate<TResponse> next)
+    {
+        cancellationToken.ThrowIfCancellationRequested();
+        if (context.IsActive)
+            throw new InvalidOperationException("不支持嵌套事务命令，请在同一个命令处理器内完成事务操作");
+        using var work = freeSql.CreateUnitOfWork();
+        work.GetOrBeginTransaction();
+        using var execution = context.Enter(work.Orm);
+        var response = await next();
+        cancellationToken.ThrowIfCancellationRequested();
+        work.Commit();
+        return response;
+        // 未提交时，工作单元释放自动回滚；执行上下文同时清理。
+    }
+}

Core/MAX.Framework/Mediation/UnitOfWorkExecutionContext.cs

@@ -0,0 +1,27 @@
+using System.Threading;
+
+namespace MAX.Framework.Mediation;
+
+/// <summary>沿当前异步调用链传递事务 ORM，隔离并行命令的执行状态。</summary>
+public sealed class UnitOfWorkExecutionContext
+{
+    private readonly AsyncLocal<IFreeSql?> _current = new();
+
+    public IFreeSql Orm => _current.Value
+        ?? throw new InvalidOperationException("当前操作必须在事务管道内执行");
+
+    public bool IsActive => _current.Value != null;
+
+    internal IDisposable Enter(IFreeSql orm)
+    {
+        if (IsActive)
+            throw new InvalidOperationException("不支持嵌套事务命令，请在同一个命令处理器内完成事务操作");
+        _current.Value = orm;
+        return new ExecutionScope(this);
+    }
+
+    private sealed class ExecutionScope(UnitOfWorkExecutionContext context) : IDisposable
+    {
+        public void Dispose() => context._current.Value = null;
+    }
+}

Core/MAX.Framework/Mediation/ValidationBehavior.cs

@@ -0,0 +1,18 @@
+using MAX.Core.Mediation;
+using MediatR;
+
+namespace MAX.Framework.Mediation;
+
+/// <summary>执行请求自身的参数校验，验证通过后才进入后续管道。</summary>
+public sealed class ValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
+    where TRequest : IRequest<TResponse>, IValidatableRequest
+{
+    public Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken,
+        RequestHandlerDelegate<TResponse> next)
+    {
+        ArgumentNullException.ThrowIfNull(request);
+        cancellationToken.ThrowIfCancellationRequested();
+        request.Validate();
+        return next();
+    }
+}