CODEWITHSUNDEEP
mongodbperformanceaggregation-framework
Victor W.
Victor W.

Reputation: 85

MongoDB unwind in find()? and Performance better in find() queries?

I have this aggregate query, which takes really long to get results and I only need the Aggregation framework because of the $unwind parameter. To be specific I have to query things that are in an array. How can I rewrite this aggregation query into a find query and do you think performance would be better with find?

db.cms.aggregate([{"$unwind":"$values"},
                       {"$match": {"values.timestamp":{"$exists":1}}},
                       {"$match": {"values.sensor":"V1"}},
                       {"$match": {"values.timestamp":{"$gte":"2018-02-07 14:00:16.163","$lte":"2018-02-07 14:00:16.163"}}}] )

The documents in the collection look like this 

_id" : ObjectId("5a8ac17569191602538b65d2"), 

"values" : [
    {
        "sensor" : "B", 
        "unit" : "mm/s2", 
        "timestamp": "2018-02-07 14:00:16.163"

    }, 
    {
        "sensor" : "Bp", 
        "unit" : "mm/s2", 
        "timestamp": "2018-02-07 14:00:16.163"
    }, 
    {
        "sensor" : "Bt", 
        "unit" : "mm/s2",
        "timestamp": "2018-02-07 14:00:16.163"
    }, 
    {
        "sensor" : "V1", 
        "timestamp" : "2018-02-07 14:00:16.163", 
        "unit" : "V" 

    }]}

Upvotes: 2

Views: 9027

Answers (1)

TechWisdom
TechWisdom

Reputation: 4305

If all you need is filtering out, simply use the $filter operator:

db.cms.aggregate([
{
    $project: {
        values : {
            $filter: {
                input: "$values",
                as: "value",
                cond: {
                    $and: [
                        { $ifNull: [ "$$value.type", false ] },
                        { $eq: [ "$$value.sensor", "V1" ] },
                        { $eq: [ "$$value.timestamp", "2018-02-07 14:00:16.163" ] },
                    ]
                }
            }
        }
    }
}
])

By the way, the cond field of the aggregational $filter operator requires an expression that resolves to a boolean value. We cannot use the $exists nor any query operator, and its aggregational equivalent is the $ifNull operator.

Upvotes: 4

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