NoMethodError: undefined method `more_results' for #<Mysql>

I am trying to create rake task to import data from my old php
application.But I can not connect to mysql database properly, when I run
Old::User.all on rails console ,I get this error :

NoMethodError: undefined method more_results' for #<Mysql> from /Library/Ruby/Gems/1.8/gems/activerecord-3.0.3/lib/active_record/connection_adapters/mysql_adapter.rb:623:inselect’
from
/Library/Ruby/Gems/1.8/gems/activerecord-3.0.3/lib/active_record/connection_adapters/abstract/database_statements.rb:7:in
select_all' from /Library/Ruby/Gems/1.8/gems/activerecord-3.0.3/lib/active_record/connection_adapters/abstract/query_cache.rb:56:inselect_all’
from
/Library/Ruby/Gems/1.8/gems/activerecord-3.0.3/lib/active_record/base.rb:467:in
find_by_sql' from /Library/Ruby/Gems/1.8/gems/activerecord-3.0.3/lib/active_record/relation.rb:64:into_a’
from
/Library/Ruby/Gems/1.8/gems/activerecord-3.0.3/lib/active_record/relation/finder_methods.rb:143:in
all' from /Library/Ruby/Gems/1.8/gems/activerecord-3.0.3/lib/active_record/base.rb:439:insend
from
/Library/Ruby/Gems/1.8/gems/activerecord-3.0.3/lib/active_record/base.rb:439:in
`all’
from (irb):1

Model class Old/user.rb

class Old::User < ActiveRecord::Base
  establish_connection "old_database"

  # Because table name is lowercase
  def self.table_name()
   "user"
  end
end

database.yml

old_database:
  adapter: mysql
  database: old_database
  username: root
  password:
  socket: /Applications/MAMP/tmp/mysql/mysql.sock