Update and delete records backed by abstract schema

I am using abstract schema to model a polymorphic has_many relation. The docs only mention how to insert records using build_assoc. There is no way to update or delete one of the has_many records. put_assoc doesn’t solve this problem as it works with the entire association, not just one. Any other ways I can update/delete a record?

Well, you can just look up the child record by its parent ID and work directly with the results?