Question about Stop Loss Trading article

[petehe]

Hi All
I have a question regarding Stop Loss Trading article
https://www.backtrader.com/blog/posts/2018-02-01-stop-trading/stop-trading/
why do we need to have a parent child order to do stop loss?

    def next(self):
        if not self.position and self.crossup > 0:
            if self.buy_order:  # something was pending
                self.cancel(self.buy_order)

            # not in the market and signal triggered
            if not self.p.buy_limit:
                self.buy_order = self.buy(transmit=False)
            else:
                price = self.data.close[0] * (1.0 - self.p.buy_limit)

                # transmit = False ... await child order before transmission
                self.buy_order = self.buy(price=price, exectype=bt.Order.Limit,
                                          transmit=False)

            # Setting parent=buy_order ... sends both together
            if not self.p.trail:
                stop_price = self.data.close[0] * (1.0 - self.p.stop_loss)
                self.sell(exectype=bt.Order.Stop, price=stop_price,
                          parent=self.buy_order)
            else:
                self.sell(exectype=bt.Order.StopTrail,
                          trailamount=self.p.trail,
                          parent=self.buy_order)

I thought we could we can use something like below to do both buy and stop loss together

self.buy(size=1, exectype=bt.Order.StopTrail, trailamount=0.25)

[ab_trader]

@petehe The line you posted issues buy trailing stop order only.