Identity Map Bug Fix

gistfile1.rb

gem 'rails', :git => 'git://github.com/rails/rails.git', :ref => 'c1f397f82c7b3f352500832a399b5dbdc500b9c8'# change as required
require 'active_record'
require 'logger'

# Show ActiveRecord log output
ActiveRecord::Base.logger = Logger.new(STDOUT)

# Print out what version we're running
puts "Active Record #{ActiveRecord::VERSION::STRING}"

# Connect to an in-memory sqlite3 database (more on this in a moment)
ActiveRecord::Base.establish_connection(
  :adapter  => 'sqlite3',
  :database => ':memory:'
)

# Create the minimal database schema necessary to reproduce the bug
ActiveRecord::Schema.define do
  create_table :posts, :force => true do |t|
  end

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

# Create the minimal set of models to reproduce the bug
class Post < ActiveRecord::Base
  has_many :comments, :dependent => :destroy
end

class Comment < ActiveRecord::Base
  belongs_to :post
  
  after_save :clear_dirty_associations_from_im
  
  # After a record is saved (if IdentityMap is enabled), check its reflections for any belongs_to associations 
  # that have a foreign key that was changed. These associated models have their entire association cache cleared.
  def clear_dirty_associations_from_im
    if ActiveRecord::IdentityMap.enabled?    
      reflections.values.each do |reflection|
        if reflection.belongs_to?
          klasses = if reflection.options[:polymorphic]
            Array(changes[reflection.foreign_type]).compact.collect(&:constantize)
          else
            Array.new(2, reflection.klass)
          end
          
          ids = changes[reflection.foreign_key] || []
          
          ActiveRecord::IdentityMap.get(klasses[0], ids[0]).try(:clear_association_cache) if klasses[0] && ids[0]
          ActiveRecord::IdentityMap.get(klasses[1], ids[1]).try(:clear_association_cache) if klasses[1] && ids[1]
        end
      end
    end
  end
end

# Create some test data
#
# If you're demonstrating an exception, then this is probably not necessary,
# but if your bug is to do with the wrong data being returned from the database,
# then you'll probably need some test data to show that.
Comment.create(:post => Post.create!)

# Demonstrate the bug fix
ActiveRecord::IdentityMap.use do
  post = Post.first
  comment = post.comments[0]
  comment.post = nil
  comment.save
  Post.destroy(post.id)
end

Comment.first != nil