execute mongodb functions from mgo golang

Question

Is it possible to use mgo driver to execute mongodb functions during an update or insert while using a struct object?

err := db.C(collectionName).UpdateId(eventID, Event{
    Name: eventName,
    Club: getClubName(clubID), //how to call mongodb getClubName function?
})

I have a mongodb function that returns a club name when given a club id. The following executes OK in the mongodb shell.

db.loadServerScripts();
db.Event.update({"_id" : "30fc..."}, {"name": "foo_bar" , "clubName": getClubName("4df32...")});

I can execute an additional database lookup to get the club name, but would prefer this to be atomic if possible.

@Speedy, did you ever figure this out? Despite Markus's dismissive comment, this is useful. The MongoDB documentation recommends using a similar function to implement an auto-increment field, for example. — Nathan Smith
– Nathan Smith, Commented Mar 8, 2016 at 23:31
@NathanSmith, I don't think mgo supports these types of queries which is a shame. Ended up replacing MongoDB with Bolt. Its much better as an embedded transactional database. Used disk space is 42 times smaller. — Speedy
– Speedy, Commented Mar 20, 2016 at 11:15

Community · Accepted Answer · 2017-05-23 12:13:34Z

1

Per this similar question, there is no way to evaluate JavaScript during an insert. I think it's a safe assumption that the same goes for updates, upserts, etc.

You can achieve this in two calls by using mgo's db.Run() method:

db.Run(bson.M{"eval": fmt.Sprintf("getClubName(%s);", clubID)}, &resp)

And then using the result in your update statement.

Unfortunately, there is no way to make things atomic using this technique. If atomicity is a requirement, I would recommend keeping all the business logic in your application and using a local or database-based locking mechanism.

edited May 23, 2017 at 12:13

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answered Mar 9, 2016 at 23:06

Nathan Smith

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