mongodb - Return min and max of a subdocument property -


suppose have following collection:

{     "title": "foo1",     "description: "bar1",     "foobars": [         {             "title": "foobar1",             "time": {                 "$date": "2013-10-04t19:53:54.714z"             }         },         {             "title": "foobar2",             "time": {                 "$date": "2013-10-06t19:53:54.714z"             }         },     ] }

how query (using mongoose) find min , max time value foobars documents. documentation seems way it, isn't working:

foomodel.aggregate({ $group: { _id: null, maxtime: { $max: '$foobars.time' }}}, callback);

$unwind foobars before group:

foomodel.aggregate(     { $unwind: '$foobars' },     { $group: { _id: null, maxtime: { $max: '$foobars.time' }}},      callback);

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