只显示文档中所有的特定字段

{
    "_id": {
        "$id": "515bb7e2a00b2add0b000001"
    },
    "user_id": "user_8888",
    "events": {
        "common test I": {
            "subject": "common test I",
            "start_date": "04/14/2013",
            "start_time": "8.00 AM",
            "end_date": "04/14/2013",
            "end_time": "10.30 AM",
            "all_day_event": "false",
            "discription": "no discription",
            "location": "STC",
            "private": "false",
            "time_zone": "IST",
            "alarm": "true",
            "alarm_threshold": "5",
            "status": "true"
        }
    }
}

只要
 {
            "subject": "common test I",
            "start_date": "04/14/2013",
            "start_time": "8.00 AM",
            "end_date": "04/14/2013",
            "end_time": "10.30 AM",
            "all_day_event": "false",
            "discription": "no discription",
            "location": "STC",
            "private": "false",
            "time_zone": "IST",
            "alarm": "true",
            "alarm_threshold": "5",
            "status": "true"
        }

db.collection.find({},{"events.common test I":1,_id:0})