Ruby-on-rails – MongoDB/Mongoid: Can one query for ObjectID in embedded documents

For the record, I'm a bit of a newbie when it comes to Rails and MongoDB.

I'm using Rails+Mongoid+MongoDB to build an app and I've noticed that Mongoid adds ObjectID to embedded documents for some reason.

Is there any way to query all documents in a collection by ObjectID both the main documents and nested ones?

If I run this command

db.programs.findOne( { _id: ObjectId( "4d1a035cfa87b171e9000002" ) } )

I get these results which is normal since I'm querying for the ObjectID at root level.

{
    "_id" : ObjectId("4d1a035cfa87b171e9000002"),
    "created_at" : "Tue Dec 28 2010 00:00:00 GMT+0000 (GMT)",
    "name" : "program",
    "routines" : [
        {
            "name" : "Day 1",
            "_id" : ObjectId("4d1a7689fa87b17f50000020")
        },
        {
            "name" : "Day 2",
            "_id" : ObjectId("4d1a7695fa87b17f50000022")
        },
        {
            "name" : "Day 3",
            "_id" : ObjectId("4d1a76acfa87b17f50000024")
        },
        {
            "name" : "Day 4",
            "_id" : ObjectId("4d1a76ecfa87b17f50000026")
        },
        {
            "name" : "Day 5",
            "_id" : ObjectId("4d1a7708fa87b17f50000028")
        },
        {
            "name" : "Day 6",
            "_id" : ObjectId("4d1a7713fa87b17f5000002a")
        },
        {
            "name" : "Day 7",
            "_id" : ObjectId("4d1a7721fa87b17f5000002c")
        }
    ],
    "user_id" : ObjectId("4d190cdbfa87b15c2900000a")
}

Now if I try to query with an ObjectID with one of the embedded document (routines) I get null like so.

db.programs.findOne( { _id: ObjectId( "4d1a7689fa87b17f50000020" ) } )
null

I know one can query embedded objects like so

db.postings.find( { "author.name" : "joe" } );

but that seems a bit redundant if you get passed an ObjectID of some sort and want to find in what document that ObjectID resides.

So I guess my question is this…

Is it possible, with some method I'm not familiar with, to query by ObjectID and search the ObjectID's in the embedded documents?

Thanks.