I've got the following doc in my db:

{
  "_id": ObjectId("ABCDEFG12345"),
  "options" : {
    "foo": "bar",
    "another": "something"
  },
  "date" : {
    "created": 1234567890,
    "updated": 0
  }
}

And I want to update options.foo and date.updated at the same time using dot notation, like so:

var mongojs = require('mongojs');

var optionName = 'foo';
var optionValue = 'baz';

var updates = {};
updates['options.' + optionName] = optionValue;
updates['date.updated'] = new Date().getTime();

db.myCollection.findAndModify({
    query : {
        _id : ObjectId('ABCDEFG12345')
    },
    update : {
        $set : updates
    },
    upsert : false,
    new : true
}, function(error, doc, result) {

    console.log(doc.options);
    console.log(doc.date);

});

And this results in:

{
  foo : 'baz',
  another : 'something'
}
{
  updated : 1234567890
}

Specifically, my pre-existing date.created field is getting clobbered even though I'm using dot notation.

Why is this only partially working? The options sub-document retains its pre-existing data (options.another), why doesn't the date sub-document retain its pre-existing data?