conversation.rb

    if connection.adapter_name =~ /mysql/i
      connection.execute <<-SQL
        UPDATE users, conversation_participants cp
        SET unread_conversations_count = unread_conversations_count + 1
        WHERE users.id = cp.user_id AND #{cp_conditions}
      SQL
    else
      User.update_all 'unread_conversations_count = unread_conversations_count + 1',
                      "id IN (SELECT user_id FROM conversation_participants cp WHERE #{cp_conditions})"
    end