Mongodb: Count specific objects in collections

Question

I want to count specific objects if present in collections like:

{
  id: 1,
  obj1: {...},
  obj2: {...}
},{
  id: 2,
  obj2: {...}
},{
  id: 3,
  obj1: {...},
  obj3: {...}
}

In above example i need the sum of count of objects(i.e. obj1, obj2, obj3). And query should return 5 in above scenario.

these are always named obj1, obj2, obj3? Three of them?

Tomasz Bubała
– Tomasz Bubała

2018-01-15 14:23:25 +00:00
Commented Jan 15, 2018 at 14:23 — Tomasz Bubała
– Tomasz Bubała, Commented Jan 15, 2018 at 14:23
yes, names will always be same

Siraj ul Haq
– Siraj ul Haq

2018-01-15 14:26:49 +00:00
Commented Jan 15, 2018 at 14:26 — Siraj ul Haq
– Siraj ul Haq, Commented Jan 15, 2018 at 14:26

s7vr · Accepted Answer · 2018-01-15 23:25:47Z

1

You can try the below $group aggregation.

$cond with $ifNull expression to check for existence of field, output 1 when present 0 when absent.

inner $sum to count values in each document with outer $sum to sum the values across collection.

db.col.aggregate([
  {
    "$group":{
      "_id":null,
      "count":{
        "$sum":{
          "$sum":[
            {"$cond":[{"$ifNull":["$obj1",false]},1,0]},
            {"$cond":[{"$ifNull":["$obj2",false]},1,0]},
            {"$cond":[{"$ifNull":["$obj3",false]},1,0]}
          ]
        }
      }
    }
  }
])

answered Jan 15, 2018 at 23:25

s7vr

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1 Comment

Siraj ul Haq Over a year ago

I have replaced inner sum with add and it worked as needed, thanks

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