Update a value in MongoDB based on its current val

问题:

I want to do something like this, but the this keyword doesn't seem to be set inside the update statement.

db.items.update({foo:…}, {$set: {bar: this.foo}}, false, true)

Do I have to use eval to accomplish this?

回答1:

Yes, you can't refer to other fields in the modifier. You'll have to use db.eval.

回答2:

Good example can be found here MongoDB: Updating documents using data from the same document