MongoDB group by aggregation query

Question

The data I have is:

[
    { type: 'software' },
    { type: 'hardware' },
    { type: 'software' },
    { type: 'network' },
    { type: 'test' },
    ...
]

I want to create a MongoDB group by aggregation pipeline to return the data like this: I only want 3 objects in result the third object in result {_id: 'other', count: 2}, This should be the sum of counts of type other that software and hardware

[
    {_id: 'software', count: 2},
    {_id: 'hardware', count: 1},
    {_id: 'other', count: 2},
]

Does this data stored in a field of a single document, or those are separate documents? — AlexZeDim
than you might wanna check and accept my answer by pressing the green mark below its rating (and probably upvote, if my answer is correct) — AlexZeDim

AlexZeDim AlexZeDim · Accepted Answer · 2021-02-16T09:01:53

This is the exact query (MongoPlayground) that you need if those data are separate documents. Just add $project stage before group and then $switch operator. (If those field data are number, you might wanna check $bucket

db.collection.aggregate([
  {
    "$project": {
      type: {
        "$switch": {
          "branches": [
            {
              "case": {
                "$eq": [
                  "$type",
                  "software"
                ]
              },
              "then": "software"
            },
            {
              "case": {
                "$eq": [
                  "$type",
                  "hardware"
                ]
              },
              "then": "hardware"
            }
          ],
          default: "other"
        }
      }
    }
  },
  {
    "$group": {
      "_id": "$type",
      "count": {
        "$sum": 1
      }
    }
  }
])

Also, I'd like to recommend avoiding field name type. Actually it doesn't reserve in MongoDB, but however it could bring conflicts with some drivers since, in schema/model files, type fields are referred to the exact BSON type of the field.

MongoDB group by aggregation query

1 Answers