Question 115483 in Mongodb Question posted in
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MongoDb Aggregate Total Count Before Grouping

I have an aggregation pipeline that groups objects and holds count for some specific field for grouped objects. You can reproduce the problem here: https://mongoplayground.net/p/2DGaiQDYDBP .

The schema is like this;

[
  {
    "_id": {
      "$oid": "63ce93ffb6e06322db59fdc0"
    },
    "fruit": "apple",
    "source": "tree",
    "is_fruit_important": "true"
  },
  {
    "_id": {
      "$oid": "63ce93ffb6e06322db59fdc1"
    },
    "fruit": "orange",
    "source": "tree",
    "is_fruit_important": "false"
  },
]

and the current query groups fruits by the source, and holds the count of important fruits for every group. After applying aggregation I get something like this after query:

[
  {
    "count": {
      "number_of_important_fruits": 1
    },
    "objects": [
      {
        "fruit": "apple",
        "id": "63ce93ffb6e06322db59fdc0",
        "is_fruit_important": "true",
        "source": "tree"
      },
      {
        "fruit": "orange",
        "id": "63ce93ffb6e06322db59fdc1",
        "is_fruit_important": "false",
        "source": "tree"
      }
    ],
    "source": {
      "source-of": "tree"
    }
  }
]

Is there a way to put the number of all fruits in the database to the response object. For example like this:

  {
    "total-count": 2,
    "result": [
      {
        "count": {
          "number_of_important_fruits": 1
        },
        "objects": [
          {
            "fruit": "apple",
            "id": "63ce93ffb6e06322db59fdc0",
            "is_fruit_important": "true",
            "source": "tree"
          },
          {
            "fruit": "orange",
            "id": "63ce93ffb6e06322db59fdc1",
            "is_fruit_important": "false",
            "source": "tree"
          }
        ],
        "source": {
          "source-of": "tree"
        }
      }
    ]
  }

They can be handled in separate aggregation pipelines but that’s what I would not like to implement. Any help would be highly appreciated.

Tags:

2

Answers


  1. 0

    You can simply add a $facet stage to push all your results into result. Then perform a $size on result to get total-count.

    db.collection.aggregate([
  ...,
  {
    "$facet": {
      "result": [],
      "total-important-count": [
        {
          $group: {
            _id: null,
            cnt: {
              $sum: "$count.number_of_important_fruits"
            }
          }
        }
      ]
    }
  },
  {
    "$addFields": {
      "total-count": {
        $size: "$result"
      },
      "total-important-count": {
        $first: "$total-important-count.cnt"
      }
    }
  }
])

    Mongo Playground

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  2. 0

    Add one additional group stage just before the final $project, using $sum with $size for a total count, or add up the important counts for a total important count.

      {$group: {
      _id: null,
      result: {$push: "$$ROOT"},
      "count_total": {$sum: {$size: "$objects"}},
      "count_important": {$sum: "$count.number_of_important_fruits"}
  }},

    Playground

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