How to find data from nested array?

Question

I have a model:

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

I need to get list of region -> city -> name (list of sities names) In the begining I tried a query to get list of (Array)city

const list = await Model.findOne(
  { $and: [{ code: req.params.code }, { 'region.name': 'Harjumaa' }] },
  { 'region.city.name': 1 },
)

And receive this data:

Then I search list of regions I send query:

Model.findOne({ code: req.params.code }, { region: 1 })

And receive data like this:

I want to get list of cities names in the same format.

My data sample:

{
  "country": "Estonia",
  "code": "ee",
  "region": [
    {
      "name": "Harjumaa",
      "city": [
        {
          "name": "Aegviidu vald",
          "latitude": "59.27941132",
          "longitude": "25.62571907"
        },
        {
          "name": "Anija vald",
          "latitude": "59.27643967",
          "longitude": "25.48167992"
        }
      ]
    }
  ]
}

can you provide sample data

ellipsis
– ellipsis

2019-02-02 09:05:40 +00:00
Commented Feb 2, 2019 at 9:05 — ellipsis
– ellipsis, Commented Feb 2, 2019 at 9:05
@AshayMandwarya Add to body

Sergei R
– Sergei R

2019-02-02 09:10:13 +00:00
Commented Feb 2, 2019 at 9:10 — Sergei R
– Sergei R, Commented Feb 2, 2019 at 9:10

mickl · Accepted Answer · 2019-02-02 11:06:42Z

1

$project with $region.city.name path will give you an array of arrays since you have two levels of nesting. To fix that you can use $reduce with $concatArrays which will flatten your final result into single array, try:

Model.aggregate([
    {
        $match: { code: "ee" }
    },
    {
        $project: {
            cityNames: {
                $reduce: {
                    input: "$region.city.name",
                    initialValue: [],
                    in: { $concatArrays: [ "$$this", "$$value" ] }
                }
            }
        }
    }
])

answered Feb 2, 2019 at 11:06

mickl

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