大家好，我是失业在家，正在找工作的博主Jerry。今天给大家介绍一个能大大减少ASP.Net Minimal WebApi编码量的方法。

我们一般会把微服务的VO和DTO封装成消息类，并作为WebApi的Request和Response参数进行网络传递。

如果使用MediatR，我们封装的消息类就要实现 MediatR Contract 接口 IRequest<> 或者INotification,  例如我的代码如下：

namespace MediatRApplication.CategoryCRUD

{public class CreateCategory : IRequest<CreateCategoryResult>{public string Message { get; set; }}public class CreateCategoryResult{public string Message { get; set; }}public class ReadCategory : IRequest<ReadCategoryResult>{public string Message { get; set; }}public class ReadCategoryResult{public string Message { get; set; }}public class UpdateCategory : IRequest<UpdateCategoryResult>{public string Message { get; set; }}public class UpdateCategoryResult{public string Message { get; set; }}public class DeleteCategory : IRequest{public string Message { get; set; }}
}

如上代码是对Category业务实体进行CRUD操作封装的DTO消息类，每个消息类都实现了MediatR的IRequest接口。有了消息类，就可以对每个消息类编写处理器（Handler）,以实现业务功能。

有了消息类，就需要为每个消息类创建WebApi接口，以实现消息的Request和Response。WebAPI接口中没有业务逻辑，只需要调用MediatR的Send方法将消息类发送给Handler即可。

但是，由于消息类比较多，一个一个创建WebApi接口是一件费时费力，并且容易出错的事情。作为一个架构师，是无法忍受程序员们干这些出力不讨好的事情的。

所以，为了项目，为了大家的Work Life Banlance, 我把创建WebApi这件事情减少成了一行代码。是的，你没看错，就是只要一行代码：

app.MapMediatorWebAPIs(typeof(CreateCategory).Assembly);

只要在ASP.Net Minimal API 项目的Progam文件中加入这一行代码，就可以把指定程序集中所有实现了IRequest<>和INotification的消息类自动生成WebAPI接口。

看起来很神奇，其实也不神奇。主要就是两个字：反射。还有泛型。

简单来说，就是在指定程序集中，通过反射查找那些类实现了IRequest<>或者INotification，然后在通过对泛型映射WebAPI方法的反射调用，为每个消息类生成WebApi接口。

Let me show you the code：

using MediatR;

using MediatRApplication;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Logging;
using System.Reflection;
using System.Xml.Linq;namespace MediatRWebAPI
{public static class MediatorWebAPIExtensions{/// <summary>/// 扩展方法,为所有MediatR Contract 消息类创建WebAPI接口/// </summary>/// <param name="app"></param>/// <param name="assemblies">Contract 消息类所在程序集</param>/// <returns></returns>public static IEndpointRouteBuilder MapMediatorWebAPIs(this IEndpointRouteBuilder app, params Assembly[] assemblies){//为所有实现了IRequest<>的消息类创建WebAPI接口Type genericRequestType = typeof(IRequest<>);var sendMethodInfo = typeof(MediatorWebAPIExtensions).GetMethod("MapMediatorSendApi", BindingFlags.NonPublic | BindingFlags.Static);foreach (var assembly in assemblies){//获取该程序集中所有实现了IRequest<>的消息类类型var requestTypes = assembly.GetTypes().Where(type => !type.IsInterface && type.GetInterfaces().Any(t => t.IsGenericType && t.GetGenericTypeDefinition() == genericRequestType));foreach (var requestType in requestTypes){//获取IRequest<>中尖括号中的泛型参数类型。var responseType = requestType.GetInterfaces().First(t => t.IsGenericType && t.GetGenericTypeDefinition() == genericRequestType).GetGenericArguments().First();//反射调用泛型映射WebApi方法var genericMethod = sendMethodInfo.MakeGenericMethod(requestType, responseType);genericMethod.Invoke(null, new object[] { app, requestType.Name });}}//为所有实现了INotification的消息类创建WebAAPI接口Type genericNotificationType = typeof(INotification);var publishMethodInfo = typeof(MediatorWebAPIExtensions).GetMethod("MapMediatorPublishApi", BindingFlags.NonPublic | BindingFlags.Static);foreach (var assembly in assemblies){//获取该程序集中所有实现了INotification的消息类类型var requestTypes = assembly.GetTypes().Where(type => !type.IsInterface && genericNotificationType.IsAssignableFrom(type));foreach (var requestType in requestTypes){//反射调用泛型映射WebApi方法var genericMethod = publishMethodInfo.MakeGenericMethod(requestType);genericMethod.Invoke(null, new object[] { app, requestType.Name });}}return app;}/// <summary>/// 为实现了IRequest<>的消息类为映射为WebAPI接口，根据消息类名称生成对应的CRUDD Http Method。/// </summary>/// <typeparam name="TRequest"></typeparam>/// <typeparam name="TResponse"></typeparam>/// <param name="app"></param>/// <param name="requestTypeName"></param>internal static void MapMediatorSendApi<TRequest, TResponse>(IEndpointRouteBuilder app, string requestTypeName) where TRequest : IRequest<TResponse>{if (requestTypeName.StartsWith("Create")) //Http Post{var uri = new Uri(requestTypeName.Replace("Create", ""), UriKind.Relative);app.MapPost(uri.ToString(), async ([FromServices] IMediator mediator, [FromBody] TRequest request) =>{TResponse response = await mediator.Send(request);return Results.Created(uri, response);}).WithName(requestTypeName).WithOpenApi();}else if (requestTypeName.StartsWith("Read")) //Http Get{var uri = new Uri(requestTypeName.Replace("Read", ""), UriKind.Relative);app.MapGet(uri.ToString(), async ([FromServices] IMediator mediator, [FromBody] TRequest request) =>{TResponse response = await mediator.Send(request);return Results.Ok(response);}).WithName(requestTypeName).WithOpenApi();}else if (requestTypeName.StartsWith("Update")) //Http Put{var uri = new Uri(requestTypeName.Replace("Update", ""), UriKind.Relative);app.MapPut(uri.ToString(), async ([FromServices] IMediator mediator, [FromBody] TRequest request) =>{TResponse response = await mediator.Send(request);return Results.Ok(response);}).WithName(requestTypeName).WithOpenApi();}else if (requestTypeName.StartsWith("Delete")) //Http Delete{var uri = new Uri(requestTypeName.Replace("Delete", ""), UriKind.Relative);app.MapDelete(uri.ToString(), async ([FromServices] IMediator mediator, [FromBody] TRequest request) =>{TResponse response = await mediator.Send(request);return Results.NoContent();}).WithName(requestTypeName).WithOpenApi();}else  //如不匹配则生成MediatR Send WebAPI接口{app.MapPost("/mediatr/send/" + requestTypeName, async ([FromServices] IMediator mediator, [FromBody] TRequest request) =>{TResponse response = await mediator.Send(request);return Results.Ok(response);}).WithName(requestTypeName).WithOpenApi();}}/// <summary>/// 为实现了INotification的消息类映射WebAPI接口。/// </summary>/// <typeparam name="TNotification"></typeparam>/// <param name="app"></param>/// <param name="requestTypeName"></param>internal static void MapMediatorPublishApi<TNotification>(IEndpointRouteBuilder app, string requestTypeName) where TNotification : INotification{app.MapPost("/mediatr/publish/" + requestTypeName, async ([FromServices] IMediator mediator, [FromBody] TNotification notification) =>{await mediator.Publish(notification);return Results.Ok();}).WithName(requestTypeName).WithOpenApi();}}
}

如上就是实现这个功能的所有代码，为了让大家看明白，我加了很多注释。如果哪位小伙伴还不明白就在下面留言。这些代码最难的地方就是对于泛型接口的处理。

我的示例项目如下，代码已经上传到了GitHub ：iamxiaozhuang/MediatRWebAPI (github.com)  大家随便用。