I have successfully followed the instructions in this post https://toolset.com/forums/topic/trying-to-automatically-create-a-fields-value/ and am creating a unique id from the post_id and the post_title.
Is there a way that instead of using the post_title I could use the postcode from an address field (using Toolset maps) in the post?
When Toolset Maps polls the Google Maps API to geocode an address it stores the returned coordinates and the full formatted address, but doesn't retain the individual address components such as postal code.
You can add some custom JS so that the post code is extracted from the returned results, for you to then "do something" with.
I have helped with this previously, where the post code extracted with JS is then used to provide the value for a postcode custom field that gets stored along with the post (and the address field). So you could then use that postcode field much like you would any other custom field.