Using data from a json document field in a Visualization

Hi Guys

I have a log which produces a field called relatedData. This field contains a small json document.
"relatedData": "{"method":"Put","StartDateTime":"2019-06-20T07:57:08.9337817+12:00","EndDateTime":"2019-06-20T07:57:08.9494062+12:00","TimeTakenInMilliSeconds":15.624500000000001}",

I'm wanting to extract the value for TimeTakenInMelliSeconds and use that number in a visualization. But not sure how to go about it.
Any ideas on how to approach this with kibana? I'm thinking it could be a scripted field but didn't see any examples of other people doing it.

Does relatedData contain the same fields in each document, or is it dynamic?

It contains different data types (sometimes json objects, sometimes strings), we have api's dumping logs and any extra information (like an exception message or a user friendly message etc) is placed in this. But we could create a new field that specifically logs this particular data object if that would make it much easier.

Creating a separate field specifically for the timestamp would definitely make this task easier. If that's not possible, however, you could probably accomplish this through a scripted field that gets the value for relatedData, parses the JSON and then extracts the TimeTakenInMilliseconds.

We do have the default @timestamp field in each document and bunch of other fields. Sorry I just provided the particular field I was interested in trying to parse. Sounds like I should be using a scripted field with a regex to pull this information out. Is that about right?

Actually now that I'm looking through the painless docs they say that regex is disabled by default for performance reasons.
