db={"user":[{"_id":ObjectId("5e36beb7b1dbae5124e4b6dc"),"business_account_id":ObjectId("5e3377bcb1dbae5124e4b6bf"),},{"_id":ObjectId("5e36d83db1dbae5124e4b732"),"business_account_id":ObjectId("5e3377bcb1dbae5124e4b6bf"),}]}

db.user.aggregate([{$facet:{not_found:[{$project:{"_id":ObjectId("5e3377bcb1dbae5124e4b6bf"),"count":{$const:0}}},{$limit:1}],found:[{"$match":{"business_account_id":ObjectId("5e3377bcb1dbae5124e4b6bf")}},{"$group":{"_id":"$business_account_id","count":{"$sum":1}}}]}},{$replaceRoot:{newRoot:{$mergeObjects:[{$arrayElemAt:["$not_found",0]},{$arrayElemAt:["$found",0]}]}}}])