Mongodb query that says "only this field" instead of having to reject each field one-by-one?

Is there a way to say "I only want this key" when you limit your query using a in Mongodb? Or do you have to always actively reject fields using {key_one:0}

For example. I only want to pull the value of key_four with my db.tonight.find().

json structure

{

  key_one : "some string",
  key_two: "some string",
  key_three : "some string",
  key_four: "some string",
  key_five: "some string",
  key_six: "some string"

}

How to simplify this?

Query:

db.tonight.find({},{_id:0,key_six:0,key_five:0,key_three:0,key_two:0,key_one:0})