"Once and only once" is the Extreme Programming phrase.

“一次且仅一次”是极限编程的座右铭。

youdao

It also makes sure dependencies are loaded once and only once.

它也确保依赖项已经加载一次，且仅加载一次。

youdao

Use QoS 2 when a message is to be delivered once and only once.

当消息仅传递一次时，使用QoS 2。

youdao

She says the only work needed once beets have been thinned is weeding and, when the weather is dry, a weekly watering.

VOA: special.2010.03.02

Milton will only use the word career once in his poetic oeuvre and it comes -- it will come pretty soon, actually, in Sonnet Number Seven.

弥尔顿在他的全部诗歌作品中只用过一次事业这个词,我们马上就会看到，在十四行诗的第七行。

耶鲁公开课 - 弥尔顿课程节选

It's a comedy that you only get once you performed and once you know what's happening, and

这种喜剧只有你自己明白，只有你自己知道发生了什么，

街头表演很有趣 - SpeakingMax英语口语达人

Once this is done, and only once it is done, does it make sense to think about action items such as making work more interesting, providing more job security, or rewarding performance with bonus plans?

FORBES: An Idiot's Guide to Employee Engagement

One particular example has it guiding users though an efficient power nap, by starting a timer once they've started dozing and only waking them once they've come out of a deeper sleep state.

ENGADGET: Sony patent application puts electrodes in a pillow, eases you out of slumber

Sanchez broke Massu's serve five times in the final and lost his own only once, and sealed victory by winning the last five games of the match.

BBC: Sanchez lands second title