Custom generate method in ax 2012 R3

I’m working around File Exchange (Export) using Data Import Export Framework (DIXF) , i want to add generate method to Find LineAmount Purchline associated with the receiving line VendPackingSlipTrans from PurchLine table.I create the following script but i need a help :

[DMFTargetTransformationAttribute(true),DMFTargetTransformationDescAttribute(“Function that generate LineAmount”),

DMFTargetTransformationSequenceAttribute(11),

DMFTargetTransFieldListAttribute([fieldStr(DMFVendPackingSlipTransEntity,LineAmount)])

]

public container GenerateLineAmount()

{

container res;

PurchLine purchLine;

VendPackingSlipTrans vendPackingSlipTrans

if(entity.LineAmount)

{

select firstOnly purchLine

where purchLine.LineAmount == entity.LineAmount &&

vendPackingSlipTrans.OrigiPurchId == purchLine.PurchId &&

vendPackingSlipTrans.PurchaseLineLine == purchLine.LineNumber;

if ( ! purchLine )

{

entity.LineAmount = purchLine.LineAmount ;

entity.insert();

}

}

res = [purchLine.LineAmount];

return res;

}

}