Is this a MS EnterLib DAAB BUG or not?

2018-01-16 15:12:01 浏览数 (1)

开门见山,使用MS Enterprise Library的DAAB(Data Access Application Block)获取数据时抛出异常。具体场景如下,通过Database对象的ExecuteReader执行两段Select语句,前一句是不合法的,后一句是正确的。为了避免第一次执行出错导致程序的终止,特意将其放到Try/Catch酷快中。两次数据库操作通过TrsanctionScope的形式纳入同一个Transaction中,具体的代码如下所示。

代码语言:js复制
   1: class Program
   2: {
   3:     static void Main()
   4:     {
   5:  
   6:         string invalidSql = "SELECT * FROM {InvalidTable}";
   7:         string validSql = "SELECT * FROM {ValidTable}";
   8:  
   9:  
  10:         Database db = DatabaseFactory.CreateDatabase();
  11:         using (TransactionScope scope = new TransactionScope())
  12:         {
  13:             DbCommand commandWithInvalidSql = db.GetSqlStringCommand(invalidSql);
  14:             DbCommand commandWithValidSql = db.GetSqlStringCommand(validSql);
  15:  
  16:             try
  17:             {
  18:                 db.ExecuteReader(commandWithInvalidSql);
  19:             }
  20:             catch
  21:             { }
  22:  
  23:             db.ExecuteReader(commandWithValidSql);
  24:         }
  25:     }
  26: } 

但是在执行第二个ExecuteReader方法的时候却抛出如下一个InvalidOperationException(如下图),错误消息为:“ExecuteReader requires an open and available Connection. The connection's current state is closed.”

原因出在这里:在ExecuteReader中,相应的ADO.NET代码放在try|catch中,当异常抛出后,相应的DbConnect会被关闭。但是由于在我的代码中,两次ExecuteReader的调用是在一个相同的Ambient Transaction中执行的,DAAB在内部采用相同的DbTransaction执行这两项操作,当执行第一项操作时,由于出现异常导致DbConnect关闭,使用相同DbConnect的第二项操作肯定会失败。

代码语言:js复制
   1: public virtual IDataReader ExecuteReader(DbCommand command)
   2: {
   3:     ConnectionWrapper wrapper = GetOpenConnection(false);
   4:  
   5:     try
   6:     {
   7: //
   8: // JS-L: I moved the PrepareCommand inside the try because it can fail.
   9: //
  10: PrepareCommand(command, wrapper.Connection);
  11:  
  12: //
  13: // If there is a current transaction, we'll be using a shared connection, so we don't
  14: // want to close the connection when we're done with the reader.
  15: //
  16: if (Transaction.Current != null)
  17:     return DoExecuteReader(command, CommandBehavior.Default);
  18: else
  19:     return DoExecuteReader(command, CommandBehavior.CloseConnection);
  20:     }
  21:     catch
  22:     {
  23: wrapper.Connection.Close();
  24: throw;
  25:     }
  26: } 
  27:  

我不清楚微软在设计的时候,是因为没有考虑到这种场景呢,还是不得以而为之,或者是出于其他因素的考虑,大家有何见解。

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