Upsert an array of items with MongoDB

I've got an array of objects I'd like to insert into a MongoDB collection, however I'd like to check if each item already exists in the collection first. If it doesn't exist then insert it, if it does exist then don't insert it.

After some Googling it looks like I'm best using the update method with the upsert property set to true.

This seems to work fine if I pass it a single item, as well as if I iterate over my array and insert the items one at a time, however I'm not sure whether this is the correct way to do this, or if it's the most efficient. Here's what I'm doing at the moment:

var data = [{}, {}, ... {}];

for (var i = 0; i < data.length; i++) {

  var item = data[i];

  collection.update(
    {userId: item.id},
    {$setOnInsert: item},
    {upsert: true},
    function(err, result) {

      if (err) {
        // Handle errors here
      }

  });

}

Is iterating over my array and inserting them one-by-one the most efficient way to do this, or is there a better way?