def failure=(exception)
      self.status.error = MigrationError.new(
        :error_message => exception.message, 
        :error_class => exception.class, 
        :error_backtrace => exception.backtrace)
    end
def failure=(exception)
      self.status.error = MigrationError.new(
        :error_message => exception.message, 
        :error_class => exception.class, 
        :error_backtrace => exception.backtrace)
    end
Sets an error to migration status