Azure Functions、.NET 6与MediatR 12的依赖注入异常问题

在.NET 6环境下的Azure HTTP Function项目中集成MediatR 12，在Startup.cs配置MediatR依赖注入时，出现以下异常：

System.MissingMethodException
HResult=0x80131513
Message=找不到方法:“Boolean Microsoft.Extensions.DependencyInjection.ServiceDescriptor.get_IsKeyedService()”。

Source=MediatR

StackTrace:
at MediatR.Registration.ServiceRegistrar.<>c.b__12_0(ServiceDescriptor service)
at System.Linq.Enumerable.WhereSelectEnumerableIterator2.MoveNext() at System.Linq.Enumerable.<OfTypeIterator>d__611.MoveNext()
at System.Linq.Enumerable.SelectManySingleSelectorIterator2.MoveNext() at System.Linq.Enumerable.WhereSelectEnumerableIterator2.MoveNext()
at System.Linq.Enumerable.Any[TSource](IEnumerable1 source, Func2 predicate)
at MediatR.Registration.ServiceRegistrar.RegisterBehaviorIfImplementationsExist(IServiceCollection services, Type behaviorType, Type subBehaviorType)
at MediatR.Registration.ServiceRegistrar.AddRequiredServices(IServiceCollection services, MediatRServiceConfiguration serviceConfiguration)
at Microsoft.Extensions.DependencyInjection.ServiceCollectionExtensions.AddMediatR(IServiceCollection services, MediatRServiceConfiguration configuration)
at TheMove.Functions.Startup.Configure(IFunctionsHostBuilder builder) in C:\Users\shamu\source\repos\TheMove\TheMove.Functions\Startup.cs:line 25
at Microsoft.Azure.WebJobs.WebJobsBuilderExtensions.ConfigureAndLogUserConfiguredServices(IWebJobsStartup startup, WebJobsBuilderContext context, IWebJobsBuilder builder, ILoggerFactory loggerFactory)
at Microsoft.Azure.WebJobs.WebJobsBuilderExtensions.UseWebJobsStartup(IWebJobsBuilder builder, Type startupType, WebJobsBuilderContext context, ILoggerFactory loggerFactory)
at Microsoft.Azure.WebJobs.WebJobsBuilderExtensions.UseExternalStartup(IWebJobsBuilder builder, IWebJobsStartupTypeLocator startupTypeLocator, WebJobsBuilderContext context, ILoggerFactory loggerFactory)
at Microsoft.Azure.WebJobs.Script.ScriptHostBuilderExtensions.<>c__DisplayClass7_0.b__1(HostBuilderContext context, IWebJobsBuilder webJobsBuilder)

相关Startup.cs代码 #

using Microsoft.Azure.Functions.Extensions.DependencyInjection;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using System;

[assembly: FunctionsStartup(typeof(TheMove.Functions.Startup))]
namespace TheMove.Functions
{
    public class Startup : FunctionsStartup
    {
        public IConfiguration Configuration { get; }

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

        public Startup() { }

        public override void Configure(IFunctionsHostBuilder builder)
        {
            if(builder != null)
            {
                var assembly = AppDomain.CurrentDomain.Load("TheMove.Application");
                builder.Services.AddMediatR(cfg =>
                {
                    cfg.RegisterServicesFromAssembly(assembly);
                });
            }
        }
    }
}

解决办法 #

这个异常的核心原因是MediatR 12依赖了.NET 7及以上版本才引入的ServiceDescriptor.IsKeyedService属性，而.NET 6环境下的Azure Functions宿主所使用的Microsoft.Extensions.DependencyInjection版本并不包含该属性，导致方法找不到。

你可以通过以下两种方式解决：

• 降级MediatR版本到11.x系列：MediatR 11.x不依赖这个.NET 7新增的属性，能完美兼容.NET 6的Azure Functions环境。直接在NuGet包管理器中把MediatR的版本回退到11.x即可。
• 强制升级依赖包版本（不推荐）：若要保留MediatR 12，需手动升级项目中Microsoft.Extensions.DependencyInjection的版本到6.0.1及以上，但可能会和Azure Functions宿主产生兼容性问题，需充分测试。

内容的提问来源于stack exchange，提问作者shamusschubert