Question

I have a Writer model that has_many books. Each book has_many orders. In order to prevent unwanted deletions, the Book model has a before_destroy hook method to make sure it isn’t referenced in the Order model, as suggested in PragProg Agile Web Dev (p.7)

Book.rb

before_destroy: :ensure_not_referenced_by_any_order

def ensure_not_referenced_by_any_order
  if orders.empty?
    return true
  else
    return false
  end
end

How would I write a before_destroy hook method for the Writer model so that for Writer.books.each, no orders exist? I started writing the below, but can’t figure out exactly how to write it.

Writer.rb

before_destroy: :ensure_books_not_referenced_by_any_order

def ensure_books_not_referenced_by_any_order
  self.books.each do |book|
    if book.orders.empty?
      return true
    else
      return false
    end
  end
end

Thanks very much for your help!

Answer 1

Couldn’t get @Mark’s suggestion to work. Resorted to restricting only for books.empty?, meaning a writer must delete all of his books first in order to delete his own profile.

def ensure_has_no_books
  if books.empty?
    return true
  else
    return false
  end
end

Please let me know if you have insight on how I can get the has_no_books_reference_by_any_order loop to work, and I will accept if it does. Thanks!