Post the outgoing invoice by code, selecting only certain order lines and adjusting the quantity if necessary

Using the following code, you can post a sales invoice for a particular sales order and process only selected lines.
The trick is to use the standard functionality of the initLinesQuery() method to create the SalesParmLine table and modify these data records before posting. For example, by deleting entire data records from the SalesParmLine.

static void createSalesInvoiceSelectLines(Args _args)
{
    SalesTable salesTable = SalesTable::find('001562');
    SalesFormLetter salesFormLetter;
    SalesParmLine salesParmLine;
    
    setPrefix(funcName());
    
    salesFormLetter = SalesFormLetter::construct(DocumentStatus::Invoice);

    // Do the steps manually, which normally are done in method salesFormLetter.update()
    salesFormLetter.salesTable(salesTable);
    salesFormLetter.initParmSalesTable(salesFormLetter.salesTable());
    salesFormLetter.transDate(systemDateGet());
    salesFormLetter.specQty(SalesUpdate::All);
    salesFormLetter.proforma(salesFormLetter.salesParmUpdate().Proforma);
    salesFormLetter.printFormLetter(salesFormLetter.printFormLetter());
    salesFormLetter.printCODLabel(NoYes::No);
    salesFormLetter.printShippingLabel(NoYes::No);
    salesFormLetter.usePrintManagement(false);
    salesFormLetter.creditRemaining(salesFormLetter.creditRemaining());

    salesFormLetter.createParmUpdateFromParmUpdateRecord(
        SalesFormletterParmData::initSalesParmUpdateFormletter(
            salesFormLetter.documentStatus(),                   
            salesFormLetter.pack(),                                                                                                                
            true,                                                                                                                
            false,                                                                                                                
            false));

    salesFormLetter.initParameters(salesFormLetter.salesParmUpdate(), Printout::Current);

    salesFormLetter.initLinesQuery();
    
    while select forupdate salesParmLine
        where salesParmLine.ParmId == salesFormLetter.parmId()
    {
        setPrefix(#PrefixField(salesParmLine, InventTransId));
        
        // ...Modify record/Delete record...
    }

    // Let's go
    if (salesFormLetter.validate(null))
    {
        salesFormLetter.run();
    }
}