how to update a record without worrying about primary key

Question

In ActiveRecord how can we update a record without worrying/knowing primary key.

If I do

Address.update(15, :user_name => 'Samuel')

it corresponds to

UPDATE addresses set user_name = 'Samuel' where id = 15

but what if i want to do:

UPDATE addresses set user_name = 'Samuel' where cid = 15

what will be the ActiveRecord equivalent of that??

I tried:

Address.update({:cid => 15}, :user_name => 'Samuel')

but that does not work.

Answer 1

a = Address.find_by_cid(15)
a.user_name = 'Samuel'
a.save

Answer 2

http://api.rubyonrails.org/classes/ActiveRecord/Base.html#M002273