[{"inventory":[{"_id":"603fb4d4dd0c9134c8ce59b7","item_id":"60145c769bd3b700087af513","createdAt":"2021-01-29T19:05:26.166Z","updatedAt":"2021-03-27T09:46:07.300Z",},{"_id":"603fb4d4dd0c9134c8ce59b8","item_id":"60145c769bd3b700087af513","createdAt":"2021-01-29T19:05:26.166Z","updatedAt":"2021-03-27T09:46:07.300Z",},]},{"inventory":[{"_id":"603fb4d4dd0c9134c8ce59b9","item_id":"60145c769bd3b700087af514","createdAt":"2021-01-29T19:05:26.166Z","updatedAt":"2021-03-27T09:46:07.300Z",},]},{"inventory":[{"_id":"603fb4d4dd0c9134c8ce10","item_id":"60145c769bd3b700087af515","createdAt":"2021-01-29T19:05:26.166Z","updatedAt":"2021-03-27T09:46:07.300Z",},{"_id":"603fb4d4dd0c9134c8ce7","item_id":"60145c769bd3b700087af515","createdAt":"2021-01-29T19:05:26.166Z","updatedAt":"2021-03-27T09:46:07.300Z",},]},]

db.collection.aggregate([{$unwind:"$inventory"},{"$replaceRoot":{"newRoot":"$inventory"}}])