mongodb array string element query

Question

I am querying array of strings in mongdb and it does not work with $gt/$lt operators, see below. "cpu" array 3rd element is string "12"

nms:PRIMARY> db.checkpoints.find({ "cpu.3": "12" }).limit(1)
{ "_id" : ObjectId("5665ed5d601be0ed56d4ca0a"), "day" : "1", "hostname" : "WAL-VSX-02", "time" : "15:33:54", "con" : [ "75", "44", "10", "25997", "8895", "13788", "338", "20", "226" ], "cpu" : [ "0", "0", "0", "12", "0", "2", "0", "0", "0" ], "__v" : 0 }
nms:PRIMARY> db.checkpoints.find({ "cpu.3": {$gte: 10}})
nms:PRIMARY>

Are you sure you want to query by a particular array index? Thats going to be very fragile code. — David says Reinstate Monica
– David says Reinstate Monica, Commented Dec 10, 2015 at 16:12

Sede · Accepted Answer · 2015-12-10 16:30:28Z

1

The only reason you are not getting any output is because "cpu" is an array of string. You will need to use the $where operator which does a JavaScript evaluation and cannot take advantage of indexes as mentioned in the documentation.

db.checkpoints.find({ "$where": function() {
    return parseFloat(this.cpu[3]) >= 10;
}})

I'll suggest you change your document structure and convert "cpu" elements to float.

answered Dec 10, 2015 at 16:30

Sede

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David says Reinstate Monica · Accepted Answer · 2015-12-10 16:18:01Z

1

You are storing the values of the cpu array as strings, but you are comparing against an integer. If you change the array to int values your query will work.

answered Dec 10, 2015 at 16:18

David says Reinstate Monica

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