c# - 为什么我在打开连接时收到 "Invalid attempt to call HasRows when reader is closed"？

Question

我有这个代码:

// this is managed elsewhere
SqlConnection connection =...
connection.Open();

// this is one block of code, separate from the above
using( var transaction = connection.BeginTransaction() ) {
   using( var command = connection.CreateCommand() ) {
     command.Transaction = transaction;
     command.CommandText = ...
     using( var reader = command.ExecuteReader() ) {
         if( reader.HasRows ) {
             if( reader.Read() ) {
                 //get data from the reader
             }
         }
     }
}

并且这段代码在大多数情况下运行得很好。但有时(很少见)检索 HasRows 会产生以下异常:

Invalid attempt to call HasRows when reader is closed.
System.InvalidOperationException
  at System.Data.SqlClient.SqlDataReader.get_HasRows()
  // my code calling HasRows listed here

我 99.5% 确信此时连接已打开。我的代码在从阅读器读取 pretty much like MSDN suggests 之前使用 HasRows .

该异常的原因可能是什么？

Answer 1

这恰好是 unexpected behavior in ExecuteReader() - 很可能是一个错误。在 ExecuteReader() 内部会发生一些随机错误，很可能是网络超时，连接被关闭，然后返回一个关闭的 SqlDataReader，就像什么都没发生一样。难怪随后调用 HasRows 会产生异常。