Add a new field to a collection with value of an existing field

Question

I'd like to add a new field to a collection, with the value of the new field set to the value of an existing field.

Specifically, I'd like to go from this:

# db.foo.findOne()     {         "_id"     : ObjectId("4f25c828eb60261eab000000"),         "created" : ISODate("2012-01-29T16:28:56.232Z"),         "..."     : ...     } 

to this:

# db.foo.findOne()     {         "_id"      : ObjectId("4f25c828eb60261eab000000"),         "created"  : ISODate("2012-01-29T16:28:56.232Z"),           "event_ts" : ISODate("2012-01-29T16:28:56.232Z"),  #same as created         "..."      : ...     } 

(New documents in this collection won't all have this peculiar redundancy, but I want to do this for my existing documents)

Answer 1

function addEventTsField(){     db.foo.find().forEach(function(doc){          db.foo.update({_id:doc._id}, {$set:{"event_ts":doc.created}});     }); } 

Run from console:

addEventTsField();