bug_522.rb

require 'active_record'
require 'logger'

puts "Active Record #{ActiveRecord::VERSION::STRING}"

ActiveRecord::Base.establish_connection(
  :adapter  => 'mysql',
  :user     => 'root',
  :database => 'test'
)

ActiveRecord::Schema.define do
  create_table :comments, :force => true do |t|
    t.integer :post_id
  end

  create_table :posts, :force => true do |t|
  end
end

class Post < ActiveRecord::Base
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

ActiveRecord::Base.logger = Logger.new(STDOUT)

Comment.joins(:post).where('posts.id IS NOT NULL').update_all(:post_id => 1)