[{"_id":"A",customer:[{id:21,order:{id:23,orderName:"orderName1"}},{id:22,order:{id:12,orderName:"Electronics"}}]},{"_id":"B",customer:[{id:21,order:{id:23,orderName:"orderName2"}},{id:22,order:{id:12,orderName:"Ele"}}]}]

db.collection.find({"customer.order.orderName":{"$regex":"Ele.+","$options":"i"}})