Question

Possible Duplicate:
In MongoDB, How to toggle a boolean field in one document with atomic operation?

I need to update a document value, “toggling” it:

The collection is “Comment” which has boolean flag “isAdmin”.

I’m going to update a given comment id, setting isAdmin false if it’s true and viceversa.

However this does not work:

db.comments.update( { "id": "xxx" }, { $set: { isAdmin: $not isAdmin } } );

What’s the right syntax?

Answer 1

You can’t reference the document you find in an update like that. You’ll need to do a query to find the document, and then do an update after you know what the value is. Two step process:

var doc = db.comments.findOne({id:"xxx"});
db.comments.update({id:"xxx"}, {$set: {isAdmin: !doc.isAdmin}});

Update:
This answer has been out of date for a while (since 2.5.2):
https://jira.mongodb.org/browse/SERVER-4362
It is now possible via the $bit operator xor, and using findOneAndUpdate to avoid two separate commands.