This comment make me thought if the best soultion is to let the user choose the values before perfoming the autocompletion.
I’m thinking in implementing the Record creation helper but instead of creating a new record it will update values of the current one.
So the idea is to shown a dropdown whenever the user adds a zip (or a city) which will be populated from the record of the country zip table (it should be possible to extend it to include external source, like the google api posted before). If the user clicks on the dropdown the other fields will be completed, otherwise we leave the values empty as we do now.
What do you think?