Question

I’m retrieving a document like this:

user = db.users.find_one( { '_id' : ObjectId( 'anID' ) } )

But I can’t figure out how to update the document if I want to change the value of ‘gender’. This doesn’t work:

newValue = { 
        'gender' : gender
        }

db.users.update( user, newValue, False )

Is my syntax wrong? What’s the best way to update user

Answer 1

Your update syntax is not correct, it should be:

update(spec, document, upsert=False, multi=False, ...)

Where spec is the same filter that you used for the find, i.e. { '_id' : ObjectId( 'anID' ) }

You can either update the document by replacing it with a modified document or use a targeted update to change only a certain value. The advantage of the targeted update is that it saves you the first round trip to the server to get the user document.

Replacement update:

user = db.users.find_one( { '_id' : ObjectId( 'anID' ) } )
user['gender'] = newGender
db.users.update( { '_id' : user['_id'] }, user, False)

Targeted update:

db.users.update( { '_id' : ObjectId( 'anID' ) }, \
                 { '$set': { 'gender' : newGender } }, False )