gistfile1.rb

# -*- coding: utf-8 -*-
module Ext
  module ActiveRecord
    module QueryBuilderExtension
      def self.included(klass)
        klass.extend ClassMethods
      end

      module ClassMethods
        def build_left_join_query(*joins)
          queries, joins = joins.flatten.partition{|q| q.is_a?(String) }
          query = queries.join(' ')
          dependency = ::ActiveRecord::Associations::ClassMethods::JoinDependency.new(self, joins, query)
          dependency.join_associations.each{|a| query << a.association_join }
          return query
        end
      end
    end
  end
end

ActiveRecord::Base.send :include, Ext::ActiveRecord::QueryBuilderExtension