[{_id:"1",accessories:{data:"{\"tyre\":\"MRF\",\"speakers\":\"bose\"}"}},{_id:"2",accessories:{model:"{}"}},{_id:"3",accessories:{data:"{\"tyre\":\"APOLLO\",\"speakers\":\"JBL\"}"}}]

db.collection.aggregate([{$set:{"accessories.dataObj":{$function:{"body":"function (data) { return JSON.parse(data); }","args":["$accessories.data"],"lang":"js"}}}},{$match:{"accessories.dataObj.tyre":"MRF"}},{$unset:"accessories.dataObj"}])