Application Techniques
Building a COM or COM+ Client

PowerBuilder clients can exercise explicit control of a transaction on a COM+ server by using a variable of type OleTxnObject instead of OLEObject to connect to the COM object.

The OleTxnObject object, derived from the OLEObject object, provides two additional functions (SetComplete and SetAbort) that enable the client to participate in transaction control. When the client calls SetComplete, the transaction is committed if no other participant in the transaction has called SetAbort or otherwise failed. If the client calls SetAbort, the transaction is always aborted.

Example

In this example, the clicked event on a button creates a variable of type OleTxnObject, connects to a COM object on a server, and calls some methods on the object. When all the methods have returned, the client calls SetComplete and disconnects from the object.

integer li_rc
OleTxnObject lotxn_obj

lotxn_obj = CREATE OleTxnObject
li_rc = lotxn_obj.ConnectToNewObject("pbcom.n_test")
IF li_rc <> 0 THEN
    Messagebox( "Connect Error", string(li_rc) )
    HALT
END IF

lotxn_obj.f_dowork()
lotxn_obj.f_domorework()

lotxn_obj.SetComplete()
lotxn_obj.DisconnectObject()

This f_dowork function on the COM object on the server creates an instance of the transaction context service and calls its DisableCommit method to prevent the transaction from committing prematurely between method calls. After completing some work, the function calls SetAbort if the work was not successfully completed and SetComplete if it was.

TransactionServer txninfo_one
integer li_rc

li_rc = GetContextService( "TransactionServer",  &
    txninfo_one )
txninfo_one.DisableCommit()

// do some work and return a return code
IF li_rc <> 0 THEN
    txninfo_one.SetAbort()
    return -1
ELSE
    txninfo_one.SetComplete()
    return 1
END IF

The SetComplete call on the client commits the transaction if all of the methods in the transaction called SetComplete or EnableCommit.