How adjust an InventTrans programatically?

Hi,
I have tried this way to do this:

In PurchFormLetter_Invoice class, at the end of the method updateNow I have included a call to a new method of PurchFormLetter created in order to include my modifications:

private void adjustInventTransMP(PurchLine _purchLine)
{
PurchTable pTable2;
InventTransAdjust _inventTransAdjust;
NumberSeq _numberSeq;
;


pTable2 = PurchTable::find( purchLine.PurchId);
if ((pTable2.TipoPedido == TipoPedido::MateriaPrima) &&
(pTable2.Portes == JJ_Portes::Debidos &&
pTable2.CosteTransporte != 0 )){
ttsbegin;
numberSeq = NumberSeq::newGetNum(InventClosing::numberSequenceReference(InventAdjustmentType::Transaction));
_inventTransAdjust = new InventTransAdjust( today(), numberSeq.num());
_inventTransAdjust.updateNow( InventTrans::findTransId( _purchLine.InventTransId, true),
NoYes::No,
NoYes::No,
pTable2.CosteTransporte);
info("Se ajustó la transaccion de inventario añadiendo el coste de transporte de MP.");
ttscommit;
}
}

Here I explain want I have done:

For some types of Purch orders (MateriaPrima) we want to include the cost of the transport in the total cost of the item purchased but not include that cost in a post to ledger because we have purch orders for transport created in other place.

So we want to adjust the physical transaction in order to include the cost of the transport in the total cost of the item purchased.

In the code of this new method I use the class InventTransAdjust to adjust the cost.

Is this code correct? I can identify the transaction of a purchline with only the InventTransId field?

Thanks guys