Question

我尝试创建一个具有 SQL 依赖项的工作服务，用于侦听表插入或更新事件。

我需要该应用程序在启动时运行任务，然后在插入和更新表事件上运行相同的任务。

任务，我需要在启动和表事件上运行

private async Task ProcessExchangeTask()
{
    using (var scope = _serviceScopeFactory.CreateScope())
    {
        _commandDispatcher = scope.ServiceProvider.GetRequiredService<ICommandDispatcher>();
        _queryDispatcher = scope.ServiceProvider.GetRequiredService<IQueryDispatcher>();

        Exchange1C exchange = null;

        do
        {
            exchange = await GetCurrentExchange(); // method return current entity (table row)

            try
            {
                if (exchange != null)
                {
                    // Incomes
                    if (exchange.ExchangeSourceTypeID == ExchangeSourceTypes.IncomeCreate)
                    {
                        await _commandDispatcher.HandleAsync(new IncomeCreateCommand(exchange));
                        continue;
                    }
                    ...

                    // other commands
                }
            }
            catch (Exception ex)
            {
                await _commandDispatcher.HandleAsync(new ExchangeErrorProcessCommand(exchange));
                _logger.Log(LogLevel.Error, ex.StackTrace);
            }
        } while (exchange != null);
    }
}

表事件处理程序

private void OnNotificationReceived(object sender, RecordChangedEventArgs<Exchange1C> e)
{
    if (e.ChangeType == ChangeType.Insert || (e.ChangeType == ChangeType.Update && e.Entity.QueueStateID == 0))
    {
        Task.WhenAll(ProcessExchangeTask());
    }
}

Worker.cs 的 ExecuteAsync 方法

protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
    // Table dependency init
    string connection = "...";
    var tableName = "Exchange1C";
    var tableDependency = new SqlTableDependency<Exchange1C>(connection, tableName, "Queues");
    tableDependency.OnChanged += OnNotificationReceived; // event listener
    tableDependency.Start();

    // Run task on worker service start. It need because maybe not processed rows in database when 
    // service start. 
    await ProcessExchangeTask();

}

问题：如果在ProcessExchangeTask运行时处理新表事件，会抛出以下异常：

<块引用>

System.InvalidOperationException：在上一个操作完成之前，在此上下文中启动了第二个操作。这通常是由使用相同 DbContext 实例的不同线程引起的。

在 Program.cs 中初始化 EF DbContext，然后注入命令处理程序。

services.AddDbContext<DbContext>(options => options.UseSqlServer(...));

.NET Core 工作服务实体框架上下文

0 个答案: