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

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

.

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1 answer


You cannot do this. Try this instead:



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

      

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