How to change the mongod db query to aggregation

Question

1. I have three queries and now I want to change this to MongoDB aggregation and below is the code:

         db.mycollection.count({$and:[$requestB:{$exists:false},[$requestC:{$exists:false}]})
         db.mycollection.count({requestB:{$exists:true}})
         db.mycollection.count({requestC:{$exists:true}})
   

2. Now i want to change this code to aggregation but it did not work

      db.mycollection.aggregate( [
    { $group: {
        '_id' : { user_id: '$user_id'},
        requestA_count: { $sum: {
            $cond: [ {$and: [{$eq: ["$requestB", null]}, {$eq: ["requestC", null]}}}, 1, 0 ]
        } },
        requestB_count: { $sum: {
            $cond: [ {requestB:{'$exists':true}}, 1, 0 ]
        } },
        requestC_count: { $sum: {
            $cond: [ {requestC:{'$exists':true}}, 1, 0 ]
        } },
    } },
    { $project: {
        _id: 0,
        user_id: '$_id.user_id',
        requestA_count: 1,
        requestB_count: 1,
        requestC_count: 1
    } }
    ] );
   

Answer 1

You can use $type instead of $exists inside $group,

db.collection.aggregate([
  {
    $group: {
      "_id": { user_id: "$user_id" },
      requestA_count: {
        $sum: {
          $cond: [
            {
              $and: [
                { $ne: [{$type: "$requestA"}, "missing"] }, 
                { $eq: [{$type: "$requestB"}, "missing"] }, 
                { $eq: [{$type: "$requestC"}, "missing"] }
              ]
            },  // you need to close bracket here not below
            1, 0
          ]
        }
      },
      requestB_count: {
        $sum: { $cond: [{ $ne: [{ $type: "$requestB" }, "missing"] }, 1, 0] }
      },
      requestC_count: {
        $sum: { $cond: [{ $ne: [ { $type: "$requestC" }, "missing" ] }, 1, 0] }
      }
    }
  },
  {
    $project: {
      _id: 0,
      user_id: "$_id.user_id",
      requestA_count: 1,
      requestB_count: 1,
      requestC_count: 1
    }
  }
])

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