How to do bulk updates of documents with values they already contain?

[DavidJBerman]

I have a collection with a lot of documents in it.  Each document has a field "tsAdded" which is a time stamp of when the document was created and added to the collection.  Now I want to add a new field, tsModified, a time stamp of when the document was last modified.  I realized I want to sort my documents by tsModified, not tsCreated, but I want to preserve my tsAdded value.  What I want to do initially is update all my documents to add the tsModified field and set the value of tsModified = tsAdded, so I can sort by tsModified right away.

In SQL to achieve this I would do something like this:

UPDATE docs

    set tsModified = tsAdded

Is it possible to do something like this in Mongo, such that Mongo will update all documents in my collection and set one field value equal to the value of another field in the same document?

Thank you.

David

[何健]

Does this meet your needs?

MongoDB shell version: 2.1.1-pre-

connecting to: test

> db.blog.find()

{ "_id" : 1, "tsAdded" : ISODate("2012-03-22T15:05:58.671Z") }

{ "_id" : 2, "tsAdded" : ISODate("2012-03-22T15:05:59.234Z") }

> db.blog.find().forEach(function(doc){doc.tsModified = doc.tsAdded;db.blog.save

(doc)})

> db.blog.find()

{ "_id" : 1, "tsAdded" : ISODate("2012-03-22T15:05:58.671Z"), "tsModified" : ISO

Date("2012-03-22T15:05:58.671Z") }

{ "_id" : 2, "tsAdded" : ISODate("2012-03-22T15:05:59.234Z"), "tsModified" : ISO

Date("2012-03-22T15:05:59.234Z") }

Thanks,
HE Jian

在 2012年3月22日星期四UTC+8下午10时49分45秒，DavidJBerman写道：

[DavidJBerman]

Jian,

  This looks to be exactly what I needed.  I'll give this a try.  Thank you very much!

David

[Scott Hernandez]

Yes, you must update each document individually after reading them.
You can also use $set to just change the one field, for example.

http://www.mongodb.org/display/DOCS/Updating

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