We would like to reduce the number of updates by using the $in operator going from

buckets = [ '2010', '2010-08', '2010-08-01' ]
buckets.each do |bucket|
@totals.update(

{ 'bucket' => bucket }

, { '$inc' => { 'downloads' => 1 }}, :upsert => true)
end

to

buckets = [ '2010', '2010-08', '2010-08-01' ]
@totals.update({ 'bucket' =>

{ "$in" => buckets }

}, { '$inc' => { 'downloads' => 1 }}, :upsert => true)

Unfortunately we get very strange and inconsistent results.

db.test.find()
db.test.update(

{"b": 2}

, { "$inc":

{ "d": 1 }

}, true)
db.test.find()

{ "_id" : ObjectId("4c6d1e345153667a3fd349b8"), "b" : 2, "d" : 1 }

db.test.update(

{"b": 3}

, { "$inc":

{ "d": 1 }

}, true)
db.test.find()

{ "_id" : ObjectId("4c6d1e345153667a3fd349b8"), "b" : 2, "d" : 1 } { "_id" : ObjectId("4c6d1e485153667a3fd349b9"), "b" : 3, "d" : 1 }

db.test.update({"b":

{ "$in": [ 2, 3, 4 ] }

}, { "$inc":

{ "d": 1 }

}, true)
db.test.find()

{ "_id" : ObjectId("4c6d1e345153667a3fd349b8"), "b" : 2, "d" : 2 } { "_id" : ObjectId("4c6d1e485153667a3fd349b9"), "b" : 3, "d" : 1 }

We would expect also

{ "_id" : ObjectId("4c6d1e485153667a3fd349ba"), "b" : 4, "d" : 1 }

to be there. Then we found there is 'multi' option to turn on in (from http://www.mongodb.org/display/DOCS/Updating )

"multi - if all documents matching criteria should be updated"

But that still does not create a documents as expected.

db.test.update({"b":

{ "$in": [ 2, 3, 4 ] }

}, { "$inc":

{ "d": 1 }

}, true, true)
db.test.find()

{ "_id" : ObjectId("4c6d1e345153667a3fd349b8"), "b" : 2, "d" : 3 } { "_id" : ObjectId("4c6d1e485153667a3fd349b9"), "b" : 3, "d" : 2 }

Now even more weird. Trying again it does create a document - but not the one expected:

db.test.update({"b":

{ "$in": [ 55, 66 ] }

}, { "$inc":

{ "d": 1 }

}, true, true)
db.test.find()

{ "_id" : ObjectId("4c6d1e345153667a3fd349b8"), "b" : 2, "d" : 3 } { "_id" : ObjectId("4c6d1e485153667a3fd349b9"), "b" : 3, "d" : 2 } { "_id" : ObjectId("4c6d1f1a5153667a3fd349ba"), "d" : 1 }

What are we missing here?