我想知道如何使用这种方式来获取数据库？

{
    "_id" : ObjectId("577c4b18b1216fd9cb1a2ffc"),
    "username" : "John",
    "todolist" : [ 
        {
            "_id" : ObjectId("577c4b36b1216fd9cb1a2ffd"),
            "newtodo" : {
                "tittle" : "Playing football"
            }
        }
    ],
    "dateAdded" : ISODate("2016-07-06T00:04:40.914Z"),
    "__v" : 0
}
{
    "_id" : ObjectId("577c4b18b1216fd9cb1a2ff