Is it possible to save data as transactions [as per firebase docs](https://firebase.google.com/docs/database/ios/read-and-write), but without overwriting the whole node? I would like to know if there is any equivalent for `updateChildValues` when calling `runTransactionBlock`. The only option I see in the docs with `runTransactionBlock` is to overwrite the existing data at /path/somepath.  

Please provide alternative or I'd appreciate your advice if I am on a wrong path here and I should not key:value to existing data.