mongodb to return object from facet

Question

Is it possible to have facet to return as an object instead of an array? It seems a bit counter intuitive to need to access result[0].total instead of just result.total

code (using mongoose):

        Model
            .aggregate()
            .match({
                "name": { "$regex": name },
                "user_id": ObjectId(req.session.user.id),
                "_id": { "$nin": except }
            })
            .facet({
                "results": [
                    { "$skip": start },
                    { "$limit": finish },
                    {
                        "$project": {
                            "map_levels": 0,
                            "template": 0
                        }
                    }
                ],
                "total": [
                    { "$count": "total" },
                ]
            })
            .exec() 

Answer 1

Each field you get using $facet represents separate aggregation pipeline and that's why you always get an array. You can use $addFields to overwrite existing total with single element. To get that first item you can use $arrayElemAt

Model
    .aggregate()
    .match({
        "name": { "$regex": name },
        "user_id": ObjectId(req.session.user.id),
        "_id": { "$nin": except }
    })
    .facet({
        "results": [
            { "$skip": start },
            { "$limit": finish },
            {
                "$project": {
                    "map_levels": 0,
                    "template": 0
                }
            }
        ],
        "total": [
            { "$count": "total" },
        ]
    })
    .addFields({
        "total": {
            $arrayElemAt: [ "$total", 0 ]
        }
    })
    .exec()

Answer 2

You can try this as well

Model
.aggregate()
.match({
  "name": { "$regex": name },
  "user_id": ObjectId(req.session.user.id),
  "_id": { "$nin": except }
})
.facet({
  "results": [
    { "$skip": start },
    { "$limit": finish },
    {
      "$project": {
        "map_levels": 0,
        "template": 0
      }
    }
  ],
  "total": [
    { "$count": "total" },
  ]
})
.addFields({
  "total": {
    "$ifNull": [{ "$arrayElemAt": [ "$total.total", 0 ] }, 0]
  }
})
.exec()