Query MongoDB to match and group nested array

Question

I have structure document like this :

// my structure
{
    "_id": ObjectId("5710e8d017487952a074027c"),
    "ID": "W1",
    "judul": "Candi Prambanan",
    "jenis": "Candi",
    "lokasi": [ 
        { "prov": "Yogyakarta" }, 
        { "kota": "Sleman" }
    ],
    "deskrip": "Candi Prambanan terletak di lingkungan Taman."
}

Now I try to use aggregate query of mongodb like this :

// query 1
db.wisata.aggregate([
    {"$unwind": "$lokasi"},
    {"$match": {
        "lokasi.kota": { "$exists": true, "$ne": null }
    }},
    {"$group": { _id: "$lokasi.kota"}}
])

//result
{
    "result": [ 
        {"_id": "Kampar" }, 
        {"_id": "Magelang"}, 
        {"_id": "Bantul"}, 
        {"_id": "Sleman"}
    ],
    "ok": 1
}

And I want use match to criteria like this:

//query 2
db.wisata.aggregate([
    {"$match": { 
       "lokasi.prov": "Yogyakarta"
    }},
    {"$group": {_id:"$lokasi.kota"}}
])

//result
{
    "result": [ 
        {"_id": ["Bantul"]}, 
        {"_id": ["Sleman"]}
    ],
    "ok": 1
}

The problem how I can use my criteria like query 2 but I get result like query 1, I have try like this :

//query 3
db.wisata.aggregate([
    {"$unwind": "$lokasi"},
    {"$match": { 
        "lokasi.prov": "Yogyakarta"
    }},
    {"$group": {_id:"$lokasi.kota"}}
])

//result
{
    "result" : [
        {"_id" : null}
    ],
    "ok" : 1
}

But result is null, please help me guys, thank you very much...

NatNgs · Accepted Answer · 2017-07-06 11:10:58Z

3

Try the following aggregate query:

db.wisata.aggregate([
    {"$match": {"lokasi.prov": "Yogyakarta"}}, 
    {"$group": {"_id": "$lokasi.kota"}},
    {"$unwind": "$_id"}
])

edited Jul 6, 2017 at 11:10

NatNgs

87414 silver badges27 bronze badges

answered May 24, 2016 at 7:55

Atish

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