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db.collection.aggregate([{"$project":{"k":"$post_id","v":{"$arrayToObject":{"$filter":{"input":{"$objectToArray":"$post"},"cond":{"$not":[{"$in":[{"$type":"$$this.v"},["object","array"]]}]}}}}}},{"$replaceRoot":{"newRoot":{"$arrayToObject":[[{k:"$k",v:"$v"}]]}}}])