Upsert Multiple Records with MongoDb

Question

I'm trying to get MongoDB to upsert multiple records with the following query, ultimately using MongoMapper and the Mongo ruby driver.

db.foo.update({event_id: { $in: [1,2]}}, {$inc: {visit:1}}, true, true)

This works fine if all the records exist, but does not create new records for records that do not exist. The following command has the desired effect from the shell, but is probably not ideal from the ruby driver.

[1,2].forEach(function(id) {db.foo.update({event_id: id}, {$inc: {visit:1}}, true, true) });

I could loop through each id I want to insert from within ruby, but that would necessitate a trip to the database for each item. Is there a way to upsert multiple items from the ruby driver with only a single trip to the database? What's the best practice here? Using mongomapper and the ruby driver, is there a way to send multiple updates in a single batch, generating something like the following?

db.foo.update({event_id: 1}, {$inc: {visit:1}}, true); db.foo.update({event_id: 2}, {$inc: {visit:1}}, true);

Sample Data:

Desired data after command if two records exist.

{ "_id" : ObjectId("4d6babbac0d8bb8238d02099"), "event_id" : 1, "visit" : 11 }
{ "_id" : ObjectId("4d6baf56c0d8bb8238d0209a"), "event_id" : 2, "visit" : 2 }

Actual data after command if two records exist.

{ "_id" : ObjectId("4d6babbac0d8bb8238d02099"), "event_id" : 1, "visit" : 11 }
{ "_id" : ObjectId("4d6baf56c0d8bb8238d0209a"), "event_id" : 2, "visit" : 2 }

Desired data after command if only the record with event_id 1 exists.

{ "_id" : ObjectId("4d6babbac0d8bb8238d02099"), "event_id" : 1, "visit" : 2 }
{ "_id" : ObjectId("4d6baf56c0d8bb8238d0209a"), "event_id" : 2, "visit" : 1 }

Actual data after command if only the record with event_id 1 exists.

{ "_id" : ObjectId("4d6babbac0d8bb8238d02099"), "event_id" : 1, "visit" : 2 }

Answer 1

This - correctly - will not insert any records with event_id 1 or 2 if they do not already exist

db.foo.update({event_id: { $in: [1,2]}}, {$inc: {visit:1}}, true, true)

This is because the objNew part of the query (see http://www.mongodb.org/display/DOCS/Updating#Updating-UpsertswithModifiers) does not have a value for field event_id. As a result, you will need at least X+1 trips to the database, where X is the number of event_ids, to ensure that you insert a record if one does not exist for a particular event_id (the +1 comes from the query above, which increases the visits counter for existing records). To say it in a different way, how does MongoDB know you want to use value 2 for the event_id and not 1? And why not 6?

W.r.t. batch insertion with ruby, I think it is possible as the following link suggests - although I've only used the Java driver: Batch insert/update using Mongoid?