无法让Polly处理折叠请求

Question

我真的和Polly很纠结

我在.NET核心Web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，我尝试使用

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

作为起点，我使用

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

这给了我一个新的

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();
    }
}

样例可以工作，但只要我将DuplicateRequestCollapser添加到项目中

我在上有一个编译错误

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

这很容易修复，我改成了

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

现在，当我运行时，我得到了这个错误

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Poly的清晰教程，特别是复制请求折叠器

有人能告诉我我哪里做错了吗？

这不是仅仅从添加包就可以工作，我甚至还没有开始集成重复请求折叠器本身！文档并不容易理解。

保罗

Answer 1

事实证明，根本原因是使用了较旧版本的包。

即使声明已经使用了3.0.2版本

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

该错误本身表明2.0.0正在使用中

System.TypeLoadException:程序集'Polly.Caching.Memory，Version=2.0.0.0，Culture=neutral，PublicKeyToken=c8a3ffc3f8f825cc‘的类型'Polly.Caching.Memory.MemoryCacheProvider’中的'Method‘Polly.Caching.Memory没有实现。

升级到3.0.2后，该异常已消失。

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：

Polly (>= 7.2.0 && < 8.0.0)

在撰写本文时，只有两个Polly版本满足这一要求: 7.2.0和7.2.1

因此，这个寓言的寓意是应该仔细检查包的版本。