Looking at the model... I think it depends on whether you want to keep the activity_hints associated with these LevelSourceHints. If you delete/destroy them all[1] you will lose any associated objects (activity_hints seems to be the only relevant thing).

Elsewhere (see the seed task for ScriptLevel, but it's kind of complex) we solve this by keeping a list of db rows that are not in the import file and delete only those rows.

[1] read here: http://api.rubyonrails.org/classes/ActiveRecord/Relation.html for difference between delete/destroy/delete_all/destroy_all