MSMQMessage Object IsFirstInTransaction Property Returns an Integer (246458)

SYMPTOMS

The IsFirstInTransaction property of a Microsoft Message Queuing MSMQMessage object returns an integer result rather than a Boolean. IsFirstInTransaction returns a 1 if the message is the first 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 first in a transaction both "message.IsFirstInTransaction" and "Not message.IsFirstInTransaction" will evaluate true. In the following example code, if the message is the first in a transaction both message boxes appear:

If message.IsFirstInTransaction Then
   MsgBox "The message was the first message sent in the transaction."
End If

If Not message.IsFirstInTransaction Then
   MsgBox "The message was not the first message sent in the transaction."
End If

RESOLUTION

There are two possible workarounds for the problem:

Explicitly test the value of the IsFirstInTransaction property against 0 and 1. A value of 1 indicates that the message is the first in the transaction, a value of 0 indicates that the message is not the first in the transaction. An example of this test is shown in the following code:
```
If MSMQMessageObject.IsFirstInTransaction = 1 Then
   MsgBox "The message was the first message sent in the transaction."
End If

If MSMQMessageObject.IsFirstInTransaction = 0 Then
   MsgBox "The message was not the first message sent in the transaction."
End If
						
```
Avoid "negative" tests that use the Not operator with the IsFirstInTransaction 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 Message Queuing and will remain consistent. Future versions of the Message Queuing 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 IsFirstInTransaction property as follows:

MSMQMessage.IsFirstInTransaction

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

REFERENCES

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

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