overriding associations problem

class User < ActiveRecord::Base
belongs_to :creator, :class_name => 'Admin', :foreign_key
=> :creator_id
end

class CreateUsers < ActiveRecord::Migration
  def self.up
    create_table :users do |t|
      t.column :name, :string
      t.column :creator_id, :string
      t.timestamps
    end
  end

  def self.down
    drop_table :users
  end
end

I override the naming associations by using the :class_name option in
the
belongs_to method. I am expecting that it is assocaited by
the :creato_id in
this case. However the error message shows that it is still looking
for
users.admin_id instead of users.creator_id though I specify the
:foreign_key. How could that be?