Forum: Ruby on Rails prevent an object from being destroyed if it has related records

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Neal L (Guest)
on 2009-03-29 20:11
(Received via mailing list)
This is a total noob question, but how do you prevent a record from
being destroyed if it has any related records.  In my case, I have a
book model and a page model.  A book has_many pages.

How do I prevent  book.destroy from destroying a book if it has
associated page records?  Is there a :dependent option that would do
this?  Do I need to do some sort of before destroy callback?

Thanks!
Andrew B. (Guest)
on 2009-03-29 20:31
(Received via mailing list)
You could always use inheritance.

class Book < ActiveRecord::Base
  def destroy
    return super if page.empty?
    return false
  end
end
Fernando P. (Guest)
on 2009-03-29 21:18
Andrew B. wrote:
> You could always use inheritance.
>
> class Book < ActiveRecord::Base
>   def destroy
>     return super if page.empty?
>     return false
>   end
> end
I think you can refactor it to:

def destroy
  page.empty? || super
end
Fernando P. (Guest)
on 2009-03-29 21:23
> I think you can refactor it to:
>
> def destroy
>   page.empty? || super
> end

My bad:

page.empty? && super

untested though :-)
Marnen L. (Guest)
on 2009-03-30 08:58
Neal L wrote:
> This is a total noob question, but how do you prevent a record from
> being destroyed if it has any related records.

The database layer can do this easily, so harness its power!  Put a
foreign key constraint in your DB with ON DELETE RESTRICT.  The Railsy
way to do this is with the excellent foreign_key_migrations plugin (see
http://github.com/harukizaemon ) -- which you should probably be using
in any case.  It works with mySQL and PostgreSQL; I'm not sure about
other database systems.

Best,
--
Marnen Laibow-Koser
removed_email_address@domain.invalid
http://www.marnen.org
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