无法让 Polly 处理折叠请求

如何解决无法让 Polly 处理折叠请求

我和波莉真的很挣扎

我在 .NET Core Web Api 应用程序中运行了以下包引用

<packagereference Include="Polly" Version="7.2.1" />
<packagereference Include="Polly.Caching.distributed" Version="3.0.1" />
<packagereference Include="Polly.Caching.Memory" Version="3.0.2" />
<packagereference Include="Polly.Contrib.DuplicateRequestCollapser" Version="0.2.1" />
<packagereference Include="Polly.Extensions.Http" Version="3.0.0" />

我的任务是使用 Polly 将多个请求压缩成一个请求

为此，我正在尝试使用

https://github.com/Polly-Contrib/Polly.Contrib.DuplicateRequestCollapser

作为我使用的起点

https://nodogmablog.bryanhogan.net/2018/11/caching-in-polly-6-and-the-httpclientfactory/#:~:text=Polly%20allows%20you%20to%20cache,you%20define%20polices%20in%20startup。

这给了我一个启动

using System;
using System.Net.Http;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Polly;
using Polly.Caching;
using Polly.Caching.Memory;
using Polly.Registry;

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMemoryCache();
        services.AddSingleton<IAsyncCacheProvider,MemoryCacheProvider>();

        IPolicyRegistry<string> registry = services.AddPolicyRegistry();

        services.AddHttpClient("RemoteServer",client =>
        {
            client.BaseAddress = new Uri("http://localhost:5000/api/");
            client.DefaultRequestHeaders.Add("Accept","application/json");
        }).AddPolicyHandlerFromregistry(PolicySelector);

        //services.AddSingleton<IRequestService,RequestService>();

        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
    }

    private IAsyncPolicy<HttpResponseMessage> PolicySelector(IReadOnlyPolicyRegistry<string> policyRegistry,HttpRequestMessage httpRequestMessage)
    {
        // you Could have some logic to select the right policy
        // see https://nodogmablog.bryanhogan.net/2018/07/polly-httpclientfactory-and-the-policy-registry-choosing-the-right-policy-based-on-the-http-request/
        return policyRegistry.Get<IAsyncPolicy<HttpResponseMessage>>("CachingPolicy");
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app,IHostingEnvironment env,IAsyncCacheProvider cacheProvider,IPolicyRegistry<string> registry)
    {
        CachePolicy<HttpResponseMessage> cachePolicy = Policy.CacheAsync<HttpResponseMessage>(cacheProvider,TimeSpan.FromSeconds(30));
        registry.Add("CachingPolicy",cachePolicy);

        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseMvc();
    }
}

示例有效，但只要我将 DuplicateRequestCollapser 添加到项目中

我有一个编译错误

CachePolicy<HttpResponseMessage> cachePolicy = Policy.CacheAsync<HttpResponseMessage>(cacheProvider,TimeSpan.FromSeconds(30));

这很容易解决，我改为

AsyncCachePolicy<HttpResponseMessage> cachePolicy = Policy.CacheAsync<HttpResponseMessage>(cacheProvider,TimeSpan.FromSeconds(30));

现在当我运行时出现错误

System.TypeLoadException: 'Method 'TryGet' in type 'Polly.Caching.Memory.MemoryCacheProvider' from 
assembly 'Polly.Caching.Memory,Version=2.0.0.0,Culture=neutral,PublicKeyToken=c8a3ffc3f8f825cc' 
does not have an implementation.'

很难找到清晰的 poly 教程，尤其是重复请求折叠器

谁能告诉我我做错了什么？

这不仅仅通过添加包起作用，我什至还没有开始集成重复请求折叠器本身！文档不易遵循

保罗

解决方法

事实证明，根本原因是使用了旧版本的软件包。

虽然说使用的是3.0.2版本

<PackageReference Include="Polly.Caching.Memory" Version="3.0.2" />

错误本身表明 2.0.0 正在使用中

System.TypeLoadException: 类型为“Polly.Caching.Memory.MemoryCacheProvider”的“方法”“TryGet”来自 程序集“Polly.Caching.Memory，版本=2.0.0.0，文化=中性，PublicKeyToken=c8a3ffc3f8f825cc” 没有实现。'

升级到 3.0.2 后异常消失了。

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即使大多数软件包需要 7.1.1 或更高版本的 Polly
Polly.Contrib.DuplicateRequestCollapser 有一个非常严格的依赖要求：

波莉 (>= 7.2.0 &&

在撰写本文时，只有两个 Polly 版本满足此要求：7.2.0 和 7.2.1

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因此，这个寓言的寓意是应该仔细检查软件包版本。