How do you update a field value in Mongo to match a different field value in the same document?

Question

I have several documents:

{"required" : 100, "total" : 30}

and I want to update the docs in such a way that require = total (regardless of the value of total). I tried:

db.collection.update({}, {"$set" : {"required" : "total"}})

but this sets it to the string literal "total", how do I access the value of the field, in this case 30

.

+3

nickponline 21 jan. 13 at 21:53

1 answer

Trang tung nguyen · Answer 1 · 2013-09-05T07:35:23+0000

You cannot do this. Try this instead:

db.collection.find().forEach(function(d) {
    d.required = d.total;
    db.collection.save(d);
});