MongoDB querying for Embeded Document

I have a mongo document which has structure like

{
"_id" : "THIS_IS_A_DHP_USER_ID+2014-11-26",
"_class" : "weight",
"items" : [
    {
        "dateTime" : ISODate("2014-11-26T08:08:38.716Z"),
        "value" : 98.5
    },
    {
        "dateTime" : ISODate("2014-11-26T08:18:38.716Z"),
        "value" : 95.5
    },
    {
        "dateTime" : ISODate("2014-11-26T08:28:38.663Z"),
        "value" : 90.5
    }
],
"source" : "MANUAL",
"to" : ISODate("2014-11-26T08:08:38.716Z"),
"from" : ISODate("2014-11-26T08:08:38.716Z"),
"userId" : "THIS_IS_A_DHP_USER_ID",
"createdDate" : ISODate("2014-11-26T08:38:38.776Z")
}
{
"_id" : "THIS_IS_A_DHP_USER_ID+2014-11-25",
"_class" : "weight",
"items" : [
    {
        "dateTime" : ISODate("2014-11-25T08:08:38.716Z"),
        "value" : 198.5
    },
    {
        "dateTime" : ISODate("2014-11-25T08:18:38.716Z"),
        "value" : 195.5
    },
    {
        "dateTime" : ISODate("2014-11-25T08:28:38.716Z"),
        "value" : 190.5
    }
],
"source" : "MANUAL",
"to" : ISODate("2014-11-25T08:08:38.716Z"),
"from" : ISODate("2014-11-25T08:08:38.716Z"),
"userId" : "THIS_IS_A_DHP_USER_ID",
"createdDate" : ISODate("2014-11-26T08:38:38.893Z")
}

I have a mongo document which has structure like { "_id" : "THIS_IS_A_DHP_USER_ID+2014-11-26", "_class" : "weight", "items" : [ { "dateTime" : ISODate("2014-11-26T08:08:38.716Z"), "value" : 98.5 }, { "dateTime" : ISODate("2014-11-26T08:18:38.716Z"), "value" : 95.5 }, { "dateTime" : ISODate("2014-11-26T08:28:38.663Z"), "value" : 90.5 } ], "source" : "MANUAL", "to" : ISODate("2014-11-26T08:08:38.716Z"), "from" : ISODate("2014-11-26T08:08:38.716Z"), "userId" : "THIS_IS_A_DHP_USER_ID", "createdDate" : ISODate("2014-11-26T08:38:38.776Z") } { "_id" : "THIS_IS_A_DHP_USER_ID+2014-11-25", "_class" : "weight", "items" : [ { "dateTime" : ISODate("2014-11-25T08:08:38.716Z"), "value" : 198.5 }, { "dateTime" : ISODate("2014-11-25T08:18:38.716Z"), "value" : 195.5 }, { "dateTime" : ISODate("2014-11-25T08:28:38.716Z"), "value" : 190.5 } ], "source" : "MANUAL", "to" : ISODate("2014-11-25T08:08:38.716Z"), "from" : ISODate("2014-11-25T08:08:38.716Z"), "userId" : "THIS_IS_A_DHP_USER_ID", "createdDate" : ISODate("2014-11-26T08:38:38.893Z") } The query that want to fire on this document structure, is for finding documents for a particular user id, unwinding the the embedded array and getting the objects that fall between a particular date range. Can an aggregation created for such a query or else is this need be solved using map-reduce kind of querying. You can do this easily with aggregation using $match $unwind and $match. You definitely don't need mapReduce.