MongoDB update. Trying to set one field from a property of another

Question

What I\'m trying to do is pretty straightforward, but I can\'t find out how to give one field the value of another.

I simply want to update one field with the character

Answer 1

As far I know the easiest way is the read and write aproach:

//At first, get/prepare your new value:
var d= db.yourColl.fetchOne({....});
d.field1== d.field2.length;

// then update with your new value
db.yourColl.save(d);