MongoDb aggregate on nested object field

Question

I have a collection of documents of format

{
    "name": <name>,
    "status": {
        "statusId": <can be a number which I want to aggregate like 1/2/3/4>
    }
}

I want to have an aggregation by status.statusId - e.g. 5 documents have status.statusId = 0, 3 documents have status.statusId = 5 etc.

I tried

db.getCollection("users").aggregate([
{
    $group: { _id: { "status":  { "statusId": "$statusId" }}, count: {$sum:1} }
}
])

but it doesn't work.

Where am I going wrong?

mickl · Accepted Answer · 2017-10-21 18:08:15Z

3

You should use the dot notation for your _id

db.getCollection("users").aggregate([
   {
      $group: { _id:  "$status.statusId", count: {$sum:1} }
   }
])

answered Oct 21, 2017 at 18:08

mickl

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