Mongodb Aggregate With Deep Nested Array

Question

Hello I tried to querying json data with mongo db with aggregate framework but get stuck, here's the data :

[{ 
    "_id" : ObjectId("5adf2294bc832359aa9bc710"), 
    "kabupaten" : "Badung", 
    "jenis_wisata" : [
        {
            "jenis" : "resto", 
            "list" : [
                {
                    "nama_resto" : "Warung Nasi Ayam Bu Oki", 
                    "alamat" : "Bukit Jimbaran"
                }, 
                {
                    "nama_resto" : "Warung Pojok Segitiga Emas", 
                    "alamat" : "Bukit Jimbaran"
                }
            ]
        }, 
        {
            "jenis" : "gunung", 
            "list" : [
                {
                    "nama_gunung" : "gunung_1", 
                    "alamat" : "alamat_1"
                }, 
                {
                    "nama_gunung" : "gunung_1", 
                    "alamat" : "alamat_1"
                }
            ]
        }
    ]
},{ 
    "_id" : ObjectId("5adf2294bc832359aa9bc711"), 
    "kabupaten" : "Denpasar", 
    "jenis_wisata" : [
        {
            "jenis" : "resto", 
            "list" : [
                {
                    "nama_resto" : "Warung Nasi Ayam Bu Oki", 
                    "alamat" : "Bukit Jimbaran"
                }, 
                {
                    "nama_resto" : "Warung Pojok Segitiga Emas", 
                    "alamat" : "Bukit Jimbaran"
                }
            ]
        }, 
        {
            "jenis" : "gunung", 
            "list" : [
                {
                    "nama_gunung" : "gunung_1", 
                    "alamat" : "alamat_1"
                }, 
                {
                    "nama_gunung" : "gunung_1", 
                    "alamat" : "alamat_1"
                }
            ]
        }
    ]
}]

what I want to achieve is to display the total amount of array "list" inside each element in array "jenis_wisata", here's the expected result that I want to achieve:

[{  
    "kabupaten" : "Badung", 
    "jenis_wisata" : [
        {
            "jenis" : "resto", 
            "total" : 2
        }, 
        {
            "jenis" : "gunung", 
            "total" : 2
        }
    ]
},{  
    "kabupaten" : "Denpasar", 
    "jenis_wisata" : [
        {
            "jenis" : "resto", 
            "total" : 2
        }, 
        {
            "jenis" : "gunung", 
            "total" : 2
        }
    ]
}]

Really appreciate your help here, Thanks

mickl · Accepted Answer · 2018-04-24 17:02:03Z

1

You need $map to transform your inner array and $size to get the length of an array.

db.collection.aggregate([
   {
       $project: {
          kabupaten: 1,
          jenis_wisata: {
             $map: {
                 input: "$jenis_wisata",
                 as: "element",
                 in: {
                    jenis: "$$element.jenis",
                    total: { $size: "$$element.list" }
                 }
              }
           }
       }
   }
])

answered Apr 24, 2018 at 17:02

mickl

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