Aggregation on complex objects

Question

I have a collection with documents like the following:

{
  "towers": [
    {
      "name": "foo",
      "towers": [
        {
          "name": "A",
          "buildType": "Apartament"
        },
        {
          "name": "B",
          "buildType": "Apartament"
        }
      ]
    },
    {
      "name": "xpto",
      "towers": [
        {
          "name": "C",
          "buildType": "House"
        },
        {
          "name": "D",
          "buildType": "Office"
        }
      ]
    }
  ]
}

All I need to know is what are all the possible values for "buildType", like:

Apartment
House
Office

It's a complex object and the data to aggregate is deep inside it. Is there any way to achieve the results I want?

Ashh · Accepted Answer · 2018-07-27 20:53:55Z

1

You need to $unwind the two nested array that is "towers" and "towers.towers" and then use $group with "towers.towers.buildType" field to get the distinct values

db.collection.aggregate([
  { "$unwind": "$towers" },
  { "$unwind": "$towers.towers" },
  { "$group": {
    "_id": "$towers.towers.buildType"
  }}
])

Output

[
  {
    "_id": "Office"
  },
  {
    "_id": "House"
  },
  {
    "_id": "Apartament"
  }
]

answered Jul 27, 2018 at 20:53

Ashh

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Comments

Rubin Porwal · Accepted Answer · 2018-07-29 16:33:08Z

0

db.collection.aggregate(

    // Pipeline
    [
        // Stage 1
        {
            $unwind: {
                path: "$towers",

            }
        },

        // Stage 2
        {
            $unwind: {
                path: "$towers.towers",
            }
        },

        // Stage 3
        {
            $group: {
                _id: '$_id',
                buildType: {
                    $addToSet: '$towers.towers.buildType'
                }
            }
        },

    ]



);

answered Jul 29, 2018 at 16:33

Rubin Porwal

3,8451 gold badge27 silver badges27 bronze badges

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