Database
[{"id":"62cd5de762c595905e37821b","letterNo":"122233","letterDate":"2023-03-01","metaData":{"name":"test","family ":"test"}},{"id":"62cd5de762c595905e37821a","letterNo":"122233","letterDate":"2023-03-01","metaData":{"type":"xxxx","where":"test"}}]
Query
db.collection.aggregate([{"$addFields":{"metaData":{"$function":{"body":"function(obj) { return JSON.stringify(obj)}","args":["$$ROOT.metaData"],"lang":"js"}}}}])