c# - 无法访问 ASP.NET Core 后台服务中的已释放对象

Question

我试图弄清楚为什么我的数据库上下文被下面的代码处理掉了。我正在尝试在整个处理阶段更新记录的状态，但是在尝试将更改保存到 htis 实体的状态字段时出现异常。

如果我在 .SaveChanges() 或 .FirstOrDefault() 调用上使用异步或非异步方法，这没有区别。

这已注册为由 IHostedService 运行

IHostedService：

public class HostedDaemon : IHostedService
{
    private readonly ILogger<HostedDaemon> _logger;
    private Timer _queueTimer;
    private Timer _runTimer;
    private IServiceProvider Services { get; set; }

    public HostedDaemon(IServiceProvider services, ILogger<HostedDaemon> logger)
    {
        Services = services;
        _logger = logger;
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        var queueAutoEvent = new AutoResetEvent(false);
        _logger.LogInformation("HostedDaemon Starting");
        _queueTimer = new Timer(QueueJobs, queueAutoEvent, TimeSpan.Zero,
            TimeSpan.FromSeconds(900));
        _runTimer = new Timer(RunQueuedJobs, queueAutoEvent, TimeSpan.Zero,
            TimeSpan.FromSeconds(10));
        return Task.CompletedTask;
    }
    public Task StopAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation("HostedDaemon Stopping");
        _queueTimer?.Change(Timeout.Infinite, 0);
        _runTimer?.Change(Timeout.Infinite, 0);
        return Task.CompletedTask;
    }
    public void Dispose()
    {
        _queueTimer?.Dispose();
        _runTimer?.Dispose();
    }

    private void QueueJobs(object stateInfo)
    {
        using (var scope = Services.CreateScope())
        {
            var autoEvent = (AutoResetEvent)stateInfo;
            var daemonProcessing = scope.ServiceProvider.GetRequiredService<IDaemonService>();
            //daemonProcessing.QueueJob();
            //daemonProcessing.RunJob();
            autoEvent.Set();
        }
    }
    private void RunQueuedJobs(object stateInfo)
    {
        using (var scope = Services.CreateScope())
        {
            var autoEvent = (AutoResetEvent)stateInfo;
            var daemonProcessing = scope.ServiceProvider.GetRequiredService<IDaemonService>();
            //daemonProcessing.QueueJob();
             daemonProcessing.RunJob(); 
            autoEvent.Set();
        }
    }
}

后台服务：

    public async Task RunJob()
    {
        try
        {
            _logger.LogInformation("Starting transaction processing");
            //TODO: Hook up SP
            var nextQueuedJob = _context.Transaction
                .Where(x => x.TransactionStatusId == (int) TransactionStatus.Queued).OrderBy(x => x.QueuedTime)
                .Include(x => x.BrokerageData).FirstOrDefault();

            if (nextQueuedJob != null)
            {
                nextQueuedJob.TransactionStatusId = (int)TransactionStatus.ProcessingData;
                _context.Transaction.Update(nextQueuedJob);
                //await _context.SaveChangesAsync();
                var brokerageData = nextQueuedJob.BrokerageData.FirstOrDefault();
                var order = JsonConvert.DeserializeObject<OrderShort>(brokerageData.BrokerageContent);

                var dynamicsSalesOrder = await CreateNewSalesOrderShort(order);
                var salesOrderLines = new List<SalesOrderLineShort>();
                foreach (var orderItem in order.Items)
                {
                    var unitPrice = (orderItem.SubTotal + orderItem.Tax)/orderItem.Quantity;
                    var salesOrderLine = new SalesOrderLineShort
                    {
                        ItemId = new Guid("42dd99ff-7133-41f7-88c5-81f922ef77dd"),
                        LineType = "Item",
                        Description = orderItem.ProductDescription,
                        UnitOfMeasureId = new Guid("cab0928b-e7af-4bd6-923f-3706b4761681"),
                        UnitPrice = unitPrice,
                        DiscountAmount = orderItem.CouponDiscountAmount,
                        Quantity = orderItem.Quantity,
                        TaxCode = "DEV"
                    };
                    salesOrderLines.Add(salesOrderLine);
                }
                nextQueuedJob.TransactionStatusId = (int)TransactionStatus.ProcessingComplete;
                await _context.SaveChangesAsync();

                nextQueuedJob.TransactionStatusId = (int)TransactionStatus.ReadyForTransfer;
                //TOOO: hook into reconciliation tables to commit an update 
                nextQueuedJob.TransactionStatusId = (int)TransactionStatus.TransferringData;

                foreach (var salesOrderLine in salesOrderLines)
                {

                    await _requestClient.PostRequest(
                        $"https://api.businesscentral.dynamics.com/v1.0/afff8eda-37c9-4c72-833b-a36dc6c8d5df/api/beta/companies/c7fdd45d-617d-47b3-adbe-7c0c69c21dd1/salesOrders/{dynamicsSalesOrder.Id}/salesOrderLines",
                        salesOrderLine);
                }

                nextQueuedJob.TransactionStatusId = (int)TransactionStatus.TransferComplete;

                nextQueuedJob.TransactionStatusId = (int)TransactionStatus.ReadyForValidation;
                nextQueuedJob.TransactionStatusId = (int)TransactionStatus.ValidatingOriginData;
                var query = new CrmQuery();
                query.UpdateOrderStatus(order.SalesOrderId, CrmQuery.OrderFIStatus.Completed,
                    order.FI_LastModified);
                nextQueuedJob.TransactionStatusId = (int)TransactionStatus.TransactionCompleted;
            }
        }
        catch (Exception e)
        {
            _logger.LogError($"exception occurred while running job.\n{e.InnerException}");
        }

    }

例外：

Message "Cannot access a disposed object. A common cause of this error
is disposing a context that was resolved from dependency injection and then
later trying to use the same context instance elsewhere in your
application.
This may occur if you are calling Dispose() on the context, or wrapping the
context in a using statement. If you are using dependency injection, you 
should let the dependency injection container take care of disposing context 
instances.\r\nObject name: 'FisEntities'."  string

启动配置：

public void ConfigureServices(IServiceCollection services)
    {
        DynamicsAccountGuid = Configuration["Services:Dynamics:AccountGuid"];
        DynamicsCompany = Configuration["Services:Dynamics:Companies:Development"];
        DynamicsBasicAuth = Configuration["Services:Dynamics:BasicAuth"];
        ConnectionString = Configuration["ConnectionStrings:FIS_Local"];

        services.AddSingleton(Configuration);
        services.AddEntityFrameworkSqlServer()
            .AddDbContext<FisEntities>(options => options.UseSqlServer(ConnectionString));

        services.Configure<CookiePolicyOptions>(options =>
        {
            // This lambda determines whether user consent for non-essential cookies is needed for a given request.
            options.CheckConsentNeeded = context => true;
            options.MinimumSameSitePolicy = SameSiteMode.None;
        });

        services.AddHttpClient<IRequestClient, DynamicsClient>("dynamics", d =>
        {
            d.BaseAddress = new Uri($"https://api.businesscentral.dynamics.com/v1.0/{DynamicsAccountGuid}/api/beta/companies/{DynamicsCompany}");
            d.DefaultRequestHeaders.Add("Authorization", DynamicsBasicAuth);
        });

        services.AddTransient<IQueueClient, CrmClient>();
        services.AddHostedService<HostedDaemon>();
        services.AddScoped<IDaemonService, TransactionService>();
        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
    }

标签： c#asp.net-coreentity-framework-core

Answer 1

在您的课堂RunQueuedJobs方法中HostedDaemon，替换daemonProcessing.RunJob();为daemonProcessing.RunJob().Wait();如下：

private void RunQueuedJobs(object stateInfo)
{
    using (var scope = Services.CreateScope())
    {
        var autoEvent = (AutoResetEvent)stateInfo;
        var daemonProcessing = scope.ServiceProvider.GetRequiredService<IDaemonService>();
        //daemonProcessing.QueueJob();
         daemonProcessing.RunJob().Wait(); // <-- Here it is
        autoEvent.Set();
    }
}

现在它应该可以正常工作了。