根据MediatR的Contract Messages自动生成Minimal WebApi接口

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。

《根据MediatR的Contract Messages自动生成Minimal 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。

《根据MediatR的Contract Messages自动生成Minimal WebApi接口》

 

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