self[:foo] vs. foo in AR models

rubyonrails-talk
1

I have an ActiveRecord model with a field called default_pic. I can’t figure out why the first example DOES NOT work and the second one does, I’m not sure why I need the self Doesn’t Work def set_default_pic default_pic = “d#{(1…8).rand}.gif” save end Works: def set_default_pic self[:default_pic] = “d#{(1…8).rand}.gif” save end

2

I have an ActiveRecord model with a field called default_pic. I can't figure out why the first example DOES NOT work and the second one does

It's a Ruby syntax thing.

def set_default_pic   default_pic = "d#{(1..8).rand}.gif"   save end

That sets a local variable named default_pic. In order to call the accessor method, you need to do

self.default_pic = "d#{(1..8).rand}.gif"

There's some page in the pickaxe which describes it. I don't have it beside me, sorry.

Pat

3

It's also an "ActiveRecord handles attributes with method_missing" thing.

The idiomatic way of doing the same thing would be to use ActiveRecord::Base#update_attribute.

   def set_default_pic      update_attribute(:default_pic, "d#{(1..8).rand}.gif")    end

Or, if this is part of a before_create callback, simply:

   def set_default_pic      write_attribute(:default_pic, "d#{(1..8).rand}.gif")    end

assuming, of course, that you have defined Range#rand somewhere to be a random item from the Range. (If not, perhaps you want (1+rand(8)) instead.)

-Rob

Rob Biedenharn http://agileconsultingllc.com Rob@AgileConsultingLLC.com