Set Field 2 to empty upon change of field 1
I have a relation of category -> subcategory -> sub-subcategory (eg.car brand -> model -> build year).
What I do is define three name fields for each category and set the latter two fields (model, build) to an automatic value list that is populated on the flow in dependence on the upper-level item. E.g. when I enter Ford as a car brand my "model" field only displays a selection of ford models. And when I decide for a model the "build" field only displays the accordingly possible build years.
What happens is, that when I enter all three fields and then change my "car brand" the other two fields remain as they are. So if I had entered "Ford -> Mustang -> 1980" before and now change the brand to BMW my fields would display a combination of "BMW -> Mustang -> 1980" - which doesn't make sense.
Now what I would like to do is force my database to automatically set the downstream fields (model, build) to empty values as soon as I change my car brand.
Do I have to make a script for each field that does the job for me upon change of the field value? Or is there a more streamlined way via the relations to solve the problem?
Thanks a lot