Aggregate data from nested array

Question

I need help with the aggregate framework. I have a model (currencies field can contain more than one object):

const schema = new mongoose.Schema({
  country: { type: String },
  code: { type: String },
  region: [{
    name: { type: String },
    path: { type: Array },
    city: [{
      name: { type: String },
      path: { type: Array },
      latitude: { type: String },
      longitude: { type: String },
    }],
  }],
  currencies: [{
    code: { type: String },
    name: { type: String },
    symbol: { type: String },
  }],
})

And I need to receive all currencies without duplicates. Received data can view like this:

[
  { code: 'string', name: 'sting', symbol: 'string' },
  { code: 'string', name: 'sting', symbol: 'string' },
  ...
]
// or like this:
[
  currencies: [
    { code: 'string', name: 'sting', symbol: 'string' },
    { code: 'string', name: 'sting', symbol: 'string' },
    ...
  ]
]

I try to create a query

Geo.aggregate([
  {
    $group: {
       _id: null,
       currencies: { $addToSet: '$currencies' },
    },
  },
])

but receive this data with duplicates and it has many nested arrays:

[
  {
    "_id": null,
    "currencies": [
      [
        {
          "_id": "5cd9486248989616a411fac5",
          "code": "JPY",
          "name": "Japanese yen",
          "symbol": "¥"
        }
      ],
      [
        {
          "_id": "5cd9491a48989616a411fb47",
          "code": "TRY",
          "name": "Turkish lira",
          "symbol": null
        }
      ],

I try this query:

Geo.aggregate([
  {
    $addFields: {
      code: '$currencies.code',
      name: '$currencies.name',
      symbol: '$currencies.symbol',
    },
  },
])

But I receive error "TypeError: item is not iterable". I need little help )

Db data views like this:

{
    "_id": {
        "$oid": "5c3334a8871695568817eadf"
    },
    "country": "Singapore",
    "code": "sg",
    "region": [
        {
            "path": [
                "Singapore"
            ],
            "_id": {
                "$oid": "5c3366c63d92ac6e531e05c0"
            },
            "city": [],
            "name": "Central Singapore Community Development Council"
        },
        ....
    ],
    "__v": 0,
    "currencies": [
        {
            "_id": {
                "$oid": "5cd948ec48989616a411fb28"
            },
            "code": "BND",
            "name": "Brunei dollar",
            "symbol": "$"
        },
        {
            "_id": {
                "$oid": "5cd948ec48989616a411fb27"
            },
            "code": "SGD",
            "name": "Singapore dollar",
            "symbol": "$"
        }
    ]
}

What are you expecting? You should show a "small" sample of data and an expected result that can actually be obtained from that sample. "Aggregate nested array" really does not explain what you expect as well as showing people would. — Neil Lunn
– Neil Lunn, Commented May 20, 2019 at 10:08
And what should be the output? Noting here that I don't see "duplicates", so make sure the "sample" demonstrates the issue and what you want. — Neil Lunn
– Neil Lunn, Commented May 20, 2019 at 10:19
@NeilLunn My text contain "And I need to receive all currencies without duplicates. Received data can view like this:" — Sergei R
– Sergei R, Commented May 20, 2019 at 10:29

Kemparaju · Accepted Answer · 2019-05-20 10:32:01Z

1

In aggregate pipeline first you need to unwind the currencies array and then group them by condition to get desired result.

Geo.aggregate([
 {
   $unwind: '$currencies'
 },
 {
     $group: {
     _id: null,
     currencies: { $addToSet: '$currencies' },
    },
 },
])

For more information you can look into documentation here

answered May 20, 2019 at 10:32

Kemparaju

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JackOfAshes - Mohit Gawande · Accepted Answer · 2019-05-20 11:06:46Z

0

db.temp.aggregate([
   {$project : {currencies : 1}}, 
   {$unwind: "$currencies"}, 
   {
      $addFields: {
         currencyHash: {
            $concat : ['$currencies.code', "--", "$currencies.name", "--", "$currencies.symbol"]
         }
      }
   },
   {
      $group: {
         _id: "$currencyHash",
         currency : {
            $first : "$currencies"
         }
      }
   },
   {
       $project: {
          code : "$currency.code",
          name : "$currency.name",
          symbol : "$currency.symbol"
       }
   },
   {
       $project: {
          _id : 0,
          currency : 0
       }
   }
]).pretty()

answered May 20, 2019 at 11:06

JackOfAshes - Mohit Gawande

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