Working with transactions in Rails

I’ve been playing around with transactions a little bit, and it seems like it will work nicely for something I need to do at work. But I’m somewhat confused with the model prefix.

For example, I have to read in folders from a directory, parse out the folder name as a generic title for the database, then go into that folder and save all of the sub-folders as a has_many relationship to the parent folder, in the same manner. But I don’t want to save the parent folder or any of its sub-folders if an exception is thrown. The content has to be tracked, so I need the information in the database.

So what I’m doing is allowing an admin to view the available content (folders in a directory that aren’t yet in the database) versus the active content (what’s already in the database). I’m allowing the content to be toggled (activated/deactivated) based on these two methods:

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# call to 'activate' a course
def load_course
  @course = Course.new
  @course.title = params[:title] if params[:title]
  Course.transaction do
    @course.save!
    read_directory(@course.folder_title).each do |f|
      lo = LearningObject.new
      lo.course_id, lo.title = @course.id, f.gsub('_',' ')
      lo.save!
    end
  end
end

# call to 'deactivate' a course
def unload_course
  unless params[:id].nil?
    @domid, @title = "available_#{params[:id]}", Course.find(params[:id]).title
    Course.transaction do
      LearningObject.destroy_all "course_id = #{params[:id]}"
      Course.destroy(params[:id])
    end
  end
end

Based on this, it would make sense to me if only the Courses table would ROLLBACK on an exception; however, I’ve tested this and it seems as though, if an exception is thrown in either case, neither the course nor the learning objects are saved. Granted, that is what I want to happen, I’m not completely convinced this will ROLLBACK the learning_objects table everytime. Do I need some sort of nested transaction, or is qualifying the block with Course good enough?