100% with being direct, but asking the Walmart girl to go on a date after a 5min conversation is a bit uncalibrated, almost creepy. Pick up on chicks while they at work rarely works in my experience but it's not impossible.
That's a good line, but if she tells me straight up that she has a boyfriend, I prefer to walk away "Cool, it was nice meeting you, good luck"
If the girl is interested she won't mention that she has a boyfriend, if she says she has one, she is not interested. Guys should avoid those kocky boyfriends lines and just move on and go approach other girls, yes she is going to smile but she has a boyfriend, it's a waste of time. If she mentions that she has a boyfriend after a while, that's a different story.