为什么我得到＆QUOT;无效试图调用HasRows当阅读器被关闭＆QUOT;以开放的连接？
问题描述：
我有这个code：
// 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
}
}
}
}
这code运行得很好的大部分时间。然而，有时 - 很少 - 检索 HasRows 产生了以下异常：
Invalid attempt to call HasRows when reader is closed.
System.InvalidOperationException
at System.Data.SqlClient.SqlDataReader.get_HasRows()
// my code calling HasRows listed here
我是99.5％，确保连接在那一刻开启。我的code使用 HasRows 从阅读器的 pretty的MSDN很像表明。
这可能是该异常的原因是什么？
What might be the reason for that exception?
答
这恰好是意外的行为在的ExecuteReader（） - 很可能是一个错误。内心深处的ExecuteReader（）一些随机的错误发生时，最有可能是网络超时，关闭连接，然后封闭 SqlDataReader的返回，就好像什么都没有发生。难怪后续调用 HasRows 产生一个例外。
This happens to be unexpected behavior in ExecuteReader() - most likely a bug. Deep inside ExecuteReader() some random error occurs, most likely a network timeout, the connection is closed and then a closed SqlDataReader is returned as if nothing happened. No wonder subsequent call to HasRows yields an exception.