根据上次消息日期，改进从事件中心读取消息的代码

Question

下面的代码连接到Azure Event Hub，它遍历所有分区，然后读取要处理的消息并插入到数据库中(待完成)，代码工作正常，但是每次它读取所有消息。

这将作为Azure WebJob安装，因此它将连续运行，实时，不停止。

1. 如何改进此代码以仅读取未处理的消息?

2. 有没有更好的方法来编码while/for部分，你会做不同的吗?

   static void Main(string[] args)
   {
       ServiceBusConnectionStringBuilder builder = new ServiceBusConnectionStringBuilder(ConfigurationManager.AppSettings["ConnectionString"].ToString());
       builder.TransportType = TransportType.Amqp;
       MessagingFactory factory = MessagingFactory.CreateFromConnectionString(ConfigurationManager.AppSettings["ConnectionString"].ToString());
       EventHubClient client = factory.CreateEventHubClient(ConfigurationManager.AppSettings["eventHubEntity"].ToString());
       EventHubConsumerGroup group = client.GetDefaultConsumerGroup();
       CancellationTokenSource cts = new CancellationTokenSource();
       System.Console.CancelKeyPress += (s, e) =>
       {
           e.Cancel = true;
           cts.Cancel();
           Console.WriteLine("Exiting...");
       };
       var d2cPartitions = client.GetRuntimeInformation().PartitionIds;
       while (true)
       {
           foreach (string partition in d2cPartitions)
           {
               EventHubReceiver receiver = group.CreateReceiver(partition, DateTime.MinValue);
               EventData data = receiver.Receive();
               Console.WriteLine("{0} {1} {2}", data.PartitionKey, data.EnqueuedTimeUtc.ToLocalTime(), Encoding.UTF8.GetString(data.GetBytes()));
               var dateLastMessage = data.EnqueuedTimeUtc.ToLocalTime();
               receiver.Close();
               client.Close();
               factory.Close();
           }
       }
   }
   

Answer 1

使用EventHubReceiver并不能给您所需的控制。相反，您应该使用EventProcessorHost，它允许使用检查点来恢复对消息的处理。

背景阅读请参见http://blogs.biztalk360.com/understanding-consumer-side-of-azure-event-hubs-checkpoint-initialoffset-eventprocessorhost/和https://blogs.msdn.microsoft.com/servicebus/2015/01/16/event-processor-host-best-practices-part-1/。

参见https://azure.microsoft.com/en-us/documentation/articles/event-hubs-csharp-ephcs-getstarted/#receive-messages-with-eventprocessorhost获取教程。

您可以轻松地在WebJob中托管EventProcessor。