Adding item positions with reference to contract in sales order

Question

Hi all,
I would be very grateful if some of you could help on this:
I have a requirement to add lines with reference to a contract while the user is creating or modificating it via VA01 or VA02. The logic flow will be as follows:
if the user enters a new item position with reference to a contract, and the qty entered exceeds the qty in the position selected of the contract, we have to skip the standard error message and try to spli the quantities in several positions with the same material in the contract.
As an example:
the contract 000000000001 has 5 lines:
line     material       qty
01       mat1           100
02       mat1           50
03       mat1           50
04       mat2           n/a
05       mat2           n/a
if the user picks up the line 02 of the contract to create a new line in the sales order, and enters 180 as qty, the sap standard will raise an error, saying the qty has exceeded the contract qty. Ok, we have to skip that error (maybe could we set it as a warning??) and 'split' the qty as follows:
in the sales orders, 3 lines will be created automatically
line    material     qty
     mat1         100
     mat1         50
     mat1         30
and of course, the released quantities in the contract must be updated: i.e the contract should be as follows:
line     material       available qty
01       mat1           0
02       mat1           0
03       mat1           20
Any ideas? : )
What i've done by the moment is to check is that 'split' is possible, in userexit_save_document. If not (e.g. if the user enters 220 for mat1 in the previous example), a custom error will appear. If it is possible, then the sales order will be created (only with the line the uswer entered) and I will trigger somehow a FM processed in background to modify the sales order.
my question now is: how can i add lines to the created sales order, making reference to some contract lines?
I've seen BAPI BAPI_SALESORDER_CREATEFROMDAT2 is used to create a document with reference, but can i use it to MODIFY an existing sales order?
any help would be greatly appreciated.
thanks a lot for your help.
regards.

Answer 1

Hello,
there's a function module called 'BAPI_SALESORDER_CHANGE', which could change a sales order. The problem could be,that these BAPI's enque the salesorder. So if you start them in background via an userexit, you have to be sure that the salesorder is updated and dequeued by posting.
An other way could be to use the exit 'userexit_check_vbap' in MV45AFZB. It's called after creating a new position or changing a position. All existing positions at that time in a internal table 'XVBAP', which you could change. (But be carefull, that you don't create an endless loop !).  
The check about the contract quantity is in a form routine called 'vbep-wmeng_pruefen_folgebeleg(sapfv45e)'.
Have a look into the form 'vbap_pruefen_ende' in FV45PFAP_VBAP_PRUEFEN_ENDE. There's the whole thing done including the call of the userexit.
Regards Wolfgang