PRB: MSMQMessage Object IsLastInTransaction Property Returns An Integer

• Microsoft Message Queue Server version 2.0

SYMPTOMS

The IsLastInTransaction property of a Microsoft Message Queue (MSMQ) MSMQMessage object returns an Integer result rather than a Boolean. IsLastInTransaction returns a 1 if the message is the last in the transaction and a 0 if it is not. This can cause logic errors in a Visual Basic (VB) program if the property is used in the expression portion of an If, While, or similar conditional statement.

When a numeric value is used in a condition statement in VB, 0 is evaluated as false and all non-zero values are evaluated as true. The Not operator in VB inverts the bits of a value when used on a numeric value. The expression "Not 1" produces the result "-2" which is considered a "true" value in a VB condition statement.

Since VB evaluates both "1" and "Not 1" as true statements, if a message is the last in a transaction both "message.IsLastInTransaction" and "Not message.IsLastInTransaction" evaluate true. In the following example code, if the message is the last in a transaction both message boxes appear:

If message.IsLastInTransaction Then
   MsgBox "The message was the last message sent in the transaction."
End If

If Not message.IsLastInTransaction Then
   MsgBox "The message was not the last message sent in the transaction."
End If 

RESOLUTION

There are two possible workarounds for the problem:

1. Explicitly test the value of the IsLastInTransaction property against 0 and 1. A value of 1 indicates that the message is the last in the transaction, a value of 0 indicates that the message is not the last in the transaction. An example of this test is shown in the following code:
   

   
   If MSMQMessageObject.IsLastInTransaction = 1 Then
      MsgBox "The message was the last message sent in the transaction."
   End If
   
   If MSMQMessageObject.IsLastInTransaction = 0 Then
      MsgBox "The message was not the last message sent in the transaction."
   End If 




2. Avoid "negative" tests that use the Not operator with the IsLastInTransaction property.

STATUS

It is safe to test explicitly for the 1 and 0 values. These values will not be changed in any future version of MSMQ and will remain consistent. Future versions of the MSMQ ActiveX components may add a property that may be evaluated as a true Boolean type for testing this characteristic.

MORE INFORMATION

The MSDN Online help describes the return values for the IsLastInTransaction property as follows:

MSMQMessage.IsLastInTransaction

Returned Value
   1 
      The message was the last message sent in the transaction. 
   0 
      The message was not the last message sent in the transaction.  

REFERENCES

MSDN Online Help for the MSMQMessage Object
Visual Basic Programmer's Guide

Q246218 MSMQMessage Object IsAuthenticated Property Returns an Integer

Q246222 MSMQQueueInfo Object IsTransactional Property Returns An Integer

Q246225 MSMQQueueInfo Object IsWorldReadable Property Returns and Integer

Q245753 MSMQQueue Object IsOpen Property Returns an Integer

Q246458 MSMQMessage Object IsFirstInTransaction Property Returns An Integer

Additional query words: MSMQ MSMQMessage IsLastInTransaction

Keywords : kbMSMQ kbDSupport
Version : winnt:2.0
Platform : winnt
Issue type : kbprb