def default_start(self, fields):
        lines = [{
            'line': line,
            'quantity': line.remaining_quantity,
            'product': line.product.id,
            'remaining_quantity': line.remaining_quantity,
            'unit': line.unit.id,
            'unit_price': line.unit_price}
            for line in self.record.lines
            if line.remaining_quantity > 0.
        ]
        return {'lines': lines}