How to upsert a document without overwriting existing fields?

[Sergey Schetinin]

Here's a use case: updating view count for a page and keeping a timestamp of the first view.

So I would do something like this: 

coll.update({'url': url}, {'first_viewed': now, '$inc': {'views': 1}}, upsert=True)

However, that would overwrite first_viewed for every update. Is there a modifier that is only applied when a document is new on upsert? Like 

coll.update({'url': url}, {'$if_new': {'first_viewed': now}, '$inc': {'views': 1}}, upsert=True)

Or possibly a modifier to set a field only if not present? Like this:

coll.update({'url': url}, {'$setdefault': {'first_viewed': now}, '$inc': {'views': 1}}, upsert=True)

Docs suggest there are none, but this seems like something a lot of people should have encountered before me.

Thanks.

-Sergey

[Sam Millman]

Not really I just do a if statement and do one or the other or use activerecord to understand new record in client side etc.

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[Sergey Schetinin]

Well, if there's no direct way to accomplish it, I recon one way to do it is to do an insert ignoring the getLastError (maybe getting the result just to be able to tell if the record is new) and then do an update. I'm not entirely sure this would be efficient. Another option is to do the upsert with the increment and check the document returned to see if the write-once property is present. If it's not, do another update setting that field.

However, it seems like it would not be too hard to support this more directly on the server side.

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[Scott Hernandez]

you want this: https://jira.mongodb.org/browse/SERVER-340

[Sergey Schetinin]

Thanks!