Efficiently querying a multidimensional array of objects in MongoDB

Question

I have documents that have the following structure:

{
    "somekey1": "somevalue1",
    "data" : [
        [
            {
                "value" : 0.807689530228178,
                "unit" : "mL"
            },
            {
                "value" : 0.7392892800962352,
                "unit" : "mL"
            },
        ],
        [
            {
                "value" : 0.8314139708574444,
                "unit" : "mL"
            },
            {
                "value" : 0.09766834482756892,
                "unit" : "mL"
            }
        ],
        [
            {
                "value" : 0.3821786847386669,
                "unit" : "mL"
            },
            {
                "value" : 0.18408410591658442,
                "unit" : "mL"
            }
        ]
   ]
}

What is the most efficient way to return all value/unit objects with value in a certain range? (ex. > 0.7?) Tried searching but didn't come up with anything helpful. Can it be done with a single find or aggregate operation?

{ "value" : 0.807689530228178, "unit" : "mL" }, { "value" : 0.7392892800962352, "unit" : "mL" }, { "value" : 0.8314139708574444, "unit" : "mL" } } — anonymous_startup
– anonymous_startup, Commented Nov 24, 2016 at 14:38

kkkkkkk · Accepted Answer · 2016-11-25 04:45:29Z

1

You could use aggregation to do it:

db.collection.aggregate([{
  $unwind: '$data',
}, {
  $unwind: '$data',
}, {
  $match: {
    'data.value': {
      $gt: 0.7
    }
  }
}, {
  $project: {
    _id: 0,
    value: "$data.value",
    unit: "$data.unit",
  },
}])

answered Nov 25, 2016 at 4:45

kkkkkkk

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