rails db structure and relationship - how to

I have a working app that needs to be copied to web app using ROR. There is a scenario i dont know how to create DB and give relationship.

There is JobType model has_many presettings i have given. eg:

there is brakes jobtype which will have 50 presettings, like that each jobtype will have more than or nearly 50 presettings.

No problem till now.

Now a car comes for service, that is called Job which might have many problem -> JobType (eg brake problem). Those 50 presettings need to be loaded for each job also now but should be editable. worker can add a comment to particular presetting that this is been done.

I have done job has_many presettings through job_entry. Since the UI works based on json response i can't add/update only particular presetting. I have to duplicate all 50 records to JobEntry(through table) table so it will be easy to update and give response. Is there any better way to do the db structure?