How to publish only unique documents in Meteor? - mongodb

Question

So I have mongodb collection with documents that some of them have the same key (beatmapset_id):
{
"_id" : "fgq7SK7LnLbcFzgSb",
"beatmapset_id" : "59049",
"version" : "Hard",
"artist" : "UNDEAD CORPORATION",
"title" : "Yoru Naku Usagi wa Yume wo Miru",
"creator" : "Strawberry"
}
{
"_id" : "u7M8wibPwxuStNLSM",
"beatmapset_id" : "59049",
"version" : "jom's Taiko Muzukashii",
"artist" : "UNDEAD CORPORATION",
"title" : "Yoru Naku Usagi wa Yume wo Miru",
"creator" : "Strawberry"
}
{
"_id" : "ChRwdj7kbPL7oYgty",
"beatmapset_id" : "59049",
"version" : "jom's Taiko Oni",
"artist" : "UNDEAD CORPORATION",
"title" : "Yoru Naku Usagi wa Yume wo Miru",
"creator" : "Strawberry"
}
How do I publish only unique documents? Something like this:
Meteor.publish("beatmaps", function() {
return Beatmaps.find({ beatmapset_id: 1 }, { unique: true });
});
Now i solve this having 2 collections. One with all documents and one where I removed those documents with this code:
db.beatmaps.ensureIndex({ beatmapset_id: 1 }, { unique: true, dropDups: true });
But it's slow and when my first collection updates I also need to update second as well. I'm sure it can be done more consistent way.