什么等于mongodb中的sql SELECT字段AS`name`

Question

有这样的资源

name: "nick"

grated: {"step1":"123","step2":"456","step3":"789"}

time: "123213123"

//and more

我想通过db.find（）获得这样的结果

{
  "axd":"nick",
  "grated": {"l1":"123","l2":"456","l3":"789"},
  time: "123213123"
}

这里name为axd，grated.step1为grated.l1，grated.step2为grated.l2，grated.step3为{{1} }，而我尝试了grated.l3，但是没有任何想法吗？