我也犯了同样的错误。发生这种情况是因为我调用了一个构造为公共异步void的方法…而不是公共async任务....

使用Startup.cs文件中的这行代码解决我的问题。 添加瞬态服务意味着每次请求该服务时，都会在您工作时创建一个新实例 与 依赖注入 服务。AddDbContext > <上下文(选项= > options.UseSqlServer (_configuration.GetConnectionString(“ContextConn”)), ServiceLifetime.Transient);

在某些情况下，当调用没有await关键字的异步方法时，会发生此错误，这可以通过在方法调用之前添加await来简单地解决。然而，答案可能与上述问题无关，但它可以帮助解决类似的错误。

首先，给alsami的答案点赞(至少)。这让我走上了正确的道路。

但是对于那些做IoC的人来说，这里有一些更深入的研究。

我的错误(和其他人一样)

发生了一个或多个错误。(第二次行动就此展开 上一个操作完成前的上下文。这通常是由于 不同的线程使用相同的DbContext实例。更多的 有关如何使用DbContext避免线程问题的信息，请参见 https://go.microsoft.com/fwlink/?linkid=2097913)。

我的代码设置。“只是基本的”……

public class MyCoolDbContext: DbContext{
    public DbSet <MySpecialObject> MySpecialObjects {        get;        set;    }
}

and

public interface IMySpecialObjectDomainData{}

和(注意MyCoolDbContext正在被注入)

public class MySpecialObjectEntityFrameworkDomainDataLayer: IMySpecialObjectDomainData{
    public MySpecialObjectEntityFrameworkDomainDataLayer(MyCoolDbContext context) {
        /* HERE IS WHERE TO SET THE BREAK POINT, HOW MANY TIMES IS THIS RUNNING??? */
        this.entityDbContext = context ?? throw new ArgumentNullException("MyCoolDbContext is null", (Exception)null);
    }
}

and

public interface IMySpecialObjectManager{}

and

public class MySpecialObjectManager: IMySpecialObjectManager
{
    public const string ErrorMessageIMySpecialObjectDomainDataIsNull = "IMySpecialObjectDomainData is null";
    private readonly IMySpecialObjectDomainData mySpecialObjectDomainData;

    public MySpecialObjectManager(IMySpecialObjectDomainData mySpecialObjectDomainData) {
        this.mySpecialObjectDomainData = mySpecialObjectDomainData ?? throw new ArgumentNullException(ErrorMessageIMySpecialObjectDomainDataIsNull, (Exception)null);
    }
}

最后，我的多线程类，从控制台应用程序(命令行接口应用程序)调用

    public interface IMySpecialObjectThatSpawnsThreads{}

and

public class MySpecialObjectThatSpawnsThreads: IMySpecialObjectThatSpawnsThreads
{
    public const string ErrorMessageIMySpecialObjectManagerIsNull = "IMySpecialObjectManager is null";

    private readonly IMySpecialObjectManager mySpecialObjectManager;

    public MySpecialObjectThatSpawnsThreads(IMySpecialObjectManager mySpecialObjectManager) {
        this.mySpecialObjectManager = mySpecialObjectManager ?? throw new ArgumentNullException(ErrorMessageIMySpecialObjectManagerIsNull, (Exception)null);
    }
}

以及DI的积累。(同样，这是一个控制台应用程序(命令行接口)…它表现出与web应用程序略有不同的行为)

private static IServiceProvider BuildDi(IConfiguration configuration) {
    /* this is being called early inside my command line application ("console application") */

    string defaultConnectionStringValue = string.Empty; /* get this value from configuration */

    ////setup our DI
    IServiceCollection servColl = new ServiceCollection()
        ////.AddLogging(loggingBuilder => loggingBuilder.AddConsole())

        /* THE BELOW TWO ARE THE ONES THAT TRIPPED ME UP.  */
        .AddTransient<IMySpecialObjectDomainData, MySpecialObjectEntityFrameworkDomainDataLayer>()
    .AddTransient<IMySpecialObjectManager, MySpecialObjectManager>()

    /* so the "ServiceLifetime.Transient" below................is what you will find most commonly on the internet search results */
     # if (MY_ORACLE)
        .AddDbContext<ProvisioningDbContext>(options => options.UseOracle(defaultConnectionStringValue), ServiceLifetime.Transient);
     # endif

     # if (MY_SQL_SERVER)
        .AddDbContext<ProvisioningDbContext>(options => options.UseSqlServer(defaultConnectionStringValue), ServiceLifetime.Transient);
     # endif

    servColl.AddSingleton <IMySpecialObjectThatSpawnsThreads,        MySpecialObjectThatSpawnsThreads>();

    ServiceProvider servProv = servColl.BuildServiceProvider();

    return servProv;
}

让我吃惊的是“transient for”的变化

        .AddTransient<IMySpecialObjectDomainData, MySpecialObjectEntityFrameworkDomainDataLayer>()
    .AddTransient<IMySpecialObjectManager, MySpecialObjectManager>()

注意，我认为因为IMySpecialObjectManager被注入到“MySpecialObjectThatSpawnsThreads”中，那些注入的对象需要是瞬态的才能完成链。

这一点是.......不只是(My)DbContext需要.Transient…而是DI图中更大的一块。

调试技巧:

这条线:

this.entityDbContext = context ?? throw new ArgumentNullException("MyCoolDbContext is null", (Exception)null);

将调试器断点放在这里。如果你的MySpecialObjectThatSpawnsThreads正在制作N个线程(例如10个线程)......这条线只被击中一次…那是你的问题。你的DbContext正在跨线程。

奖金:

我建议你阅读下面这篇文章(很老但很好)，关于网络应用程序和主机应用程序的区别

https://mehdi.me/ambient-dbcontext-in-ef6/

这里是文章的标题，以防链接发生变化。

使用实体框架6正确地管理dbcontext:深入 Mehdi El Gueddari导游

我用WorkFlowCore https://github.com/danielgerlag/workflow-core解决了这个问题

  <ItemGroup>
    <PackageReference Include="WorkflowCore" Version="3.1.5" />
  </ItemGroup>

示例代码如下..帮助未来的互联网搜索者

 namespace MyCompany.Proofs.WorkFlowCoreProof.BusinessLayer.Workflows.MySpecialObjectInterview.Workflows
    {
        using System;
        using MyCompany.Proofs.WorkFlowCoreProof.BusinessLayer.Workflows.MySpecialObjectInterview.Constants;
        using MyCompany.Proofs.WorkFlowCoreProof.BusinessLayer.Workflows.MySpecialObjectInterview.Glue;
        using MyCompany.Proofs.WorkFlowCoreProof.BusinessLayer.Workflows.WorkflowSteps;

        using WorkflowCore.Interface;
        using WorkflowCore.Models;

        public class MySpecialObjectInterviewDefaultWorkflow : IWorkflow<MySpecialObjectInterviewPassThroughData>
        {
            public const string WorkFlowId = "MySpecialObjectInterviewWorkflowId";

            public const int WorkFlowVersion = 1;

            public string Id => WorkFlowId;

            public int Version => WorkFlowVersion;

            public void Build(IWorkflowBuilder<MySpecialObjectInterviewPassThroughData> builder)
            {
                builder
                             .StartWith(context =>
                    {
                        Console.WriteLine("Starting workflow...");
                        return ExecutionResult.Next();
                    })

                        /* bunch of other Steps here that were using IMySpecialObjectManager.. here is where my DbContext was getting cross-threaded */


                    .Then(lastContext =>
                    {
                        Console.WriteLine();

                        bool wroteConcreteMsg = false;
                        if (null != lastContext && null != lastContext.Workflow && null != lastContext.Workflow.Data)
                        {
                            MySpecialObjectInterviewPassThroughData castItem = lastContext.Workflow.Data as MySpecialObjectInterviewPassThroughData;
                            if (null != castItem)
                            {
                                Console.WriteLine("MySpecialObjectInterviewDefaultWorkflow complete :)  {0}   -> {1}", castItem.PropertyOne, castItem.PropertyTwo);
                                wroteConcreteMsg = true;
                            }
                        }

                        if (!wroteConcreteMsg)
                        {
                            Console.WriteLine("MySpecialObjectInterviewDefaultWorkflow complete (.Data did not cast)");
                        }

                        return ExecutionResult.Next();
                    }))

                    .OnError(WorkflowCore.Models.WorkflowErrorHandling.Retry, TimeSpan.FromSeconds(60));

            }
        }
    }

and

ICollection<string> workFlowGeneratedIds = new List<string>();
                for (int i = 0; i < 10; i++)
                {
                    MySpecialObjectInterviewPassThroughData currentMySpecialObjectInterviewPassThroughData = new MySpecialObjectInterviewPassThroughData();
                    currentMySpecialObjectInterviewPassThroughData.MySpecialObjectInterviewPassThroughDataSurrogateKey = i;

                    ////  private readonly IWorkflowHost workflowHost;
                    string wfid = await this.workflowHost.StartWorkflow(MySpecialObjectInterviewDefaultWorkflow.WorkFlowId, MySpecialObjectInterviewDefaultWorkflow.WorkFlowVersion, currentMySpecialObjectInterviewPassThroughData);
                    workFlowGeneratedIds.Add(wfid);
                }

我设法通过将IQueryable传入一个方法，然后使用IQueryable“列表”作为另一个查询的一部分，以相同的上下文来获得这个错误。

public void FirstMethod()
{
    // This is returning an IQueryable
    var stockItems = _dbContext.StockItems
        .Where(st => st.IsSomething);

    SecondMethod(stockItems);
}

public void SecondMethod(IEnumerable<Stock> stockItems)
{
    var grnTrans = _dbContext.InvoiceLines
        .Where(il => stockItems.Contains(il.StockItem))
        .ToList();
}

为了阻止这种情况发生，我使用了这里的方法，并在传递第二个方法之前将该列表物化，通过将对SecondMethod的调用更改为SecondMethod(stockItems.ToList()

我也遇到过同样的问题，但原因不是上面列出的那些。我创建了一个任务，在任务内部创建了一个作用域，并要求容器获取服务。这工作得很好，但后来我在任务中使用了第二个服务，我忘记了也要求它到新的范围。因此，第二个服务使用的DbContext已经被处理了。

Task task = Task.Run(() =>
    {
        using (var scope = serviceScopeFactory.CreateScope())
        {
            var otherOfferService = scope.ServiceProvider.GetService<IOfferService>();
            // everything was ok here. then I did: 
            productService.DoSomething(); // (from the main scope) and this failed because the db context associated to that service was already disposed.
            ...
        }
    }

我应该这样做的:

var otherProductService = scope.ServiceProvider.GetService<IProductService>();
otherProductService.DoSomething();