multi_connection.rb

class CQM < ActiveRecord::Base
  self.abstract_class = true

  establish_connection(
    :adapter  => "mysql2",
    :host     => "localhost",
    :username => "root",
    :password => "root",
    :database => "cqm_development"
  )
end

class Abend < CQM
end

class BlueIdeas < ActiveRecord::Base
  self.abstract_class = true

  establish_connection(
    :adapter  => "mysql2",
    :host     => "localhost",
    :username => "root",
    :password => "root",
    :database => "blue-ideas_development"
  )
end

class Comment < BlueIdeas
end

Comment.transaction do
  Comment.create :user_id => 1, :idea_id => 1, :body => "ROLLBACKS!"

  Abend.transaction do
    Abend.create :job_id => 1, :return_code => 1, :abended_on => Time.now
  end

  raise "oh noes!"
end

multi_connection_dynamic.rb

class Log < ActiveRecord::Base
end

class Comment < ActiveRecord::Base
end

Comment.establish_connection(
  :adapter  => "mysql2",
  :host     => "localhost",
  :username => "root",
  :password => "root",
  :database => "blue-ideas_development"
)

Log.establish_connection(
  :adapter  => "mysql2",
  :host     => "localhost",
  :username => "root",
  :password => "root",
  :database => "blue-ideas_development"
)

Comment.transaction do
  Comment.create :user_id => 1, :idea_id => 1, :body => "ROLLBACKS!"

  Log.transaction do
    Log.create :description => "SHIT|"
  end

  raise "oh noes!"
end