.rb

module AppEngine
  module Datastore
    class << self
      alias convert_exceptions_ORIG convert_exceptions
      def convert_exceptions
        begin
          convert_exceptions_ORIG do
            yield
          end
        rescue com.google.apphosting.api.ApiProxy::ApplicationException => ex
          case ex.message
          when /ApplicationError: 2: too much contention on these datastore entities. please try again./
            raise TransactionFailed, ex.message
          when /ApplicationError: 5: Unknown/
            raise Timeout, ex.message
          when /ApplicationError: 90000: Deadlined while in scheduler/
            raise Timeout, ex.message
          else
            raise ex
          end
        rescue com.google.apphosting.api.ApiProxy::ApiDeadlineExceededException => ex
          raise Timeout, ex.message
        end
      end
    end
  end
end