Question

This is probably very stupid question but here we go

class Foo < ActiveRecord::Base
 attr_accessor :group_id
end

From irb

# gets record which has group_id set to 106    
foo = Foo.find(1)
foo.group_id
=> nil

If I go and remove

attr_accessor :group_id

All works as it should

foo = Foo.find(1)
foo.group_id
=> 106

My question is why? Shouldn’t attr_accessor create accessor / mutator for property :group_id and that why all should be working. What am I missing?

Update

Good answers bellow, just as explanation for my motivation here is I want to use mass assignment of certain properties (you need this since Rails 3.2.x). For that you need attr_accessible , I find that code is much cleaner that way, of course if used responsibly 🙂

Answer 1

Looks like group_id is already a property on your Foo object (shown by the fact that it returns 106 when attr_accessor is omitted). By adding attr_accessor you are overriding what’s already there and creating a method reader and writer called group_id. The return of the newly defined group_id is nil since you don’t define anything.

Conceptually, you’re ending up with something like this:

class Foo < ActiveRecord::Base
  def group_id  # overriding previous definition of 'group_id'
    nil
  end
end

---

Edit:

If your goal is expose properties then yes, use attr_accessible