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db.collection.aggregate([{"$project":{"members":{"$reduce":{"input":{"$map":{"input":"$clients","in":{"$concatArrays":[[{"userID":"$userID","userType":"$userType"},{"userID":"$$this.userID","userType":"$$this.userType"}],"$$this.members"]}}},"initialValue":[],"in":{"$concatArrays":["$$this","$$value"]}}}}}])