Question

我有一个翻译表，我希望每次更新都能自动记录在TranslationHistory表中。

我为此目的创建了这个触发器。

CREATE TRIGGER TranslationUpdate AFTER UPDATE ON Translation FOR EACH ROW BEGIN
   DECLARE N DATETIME;
   DECLARE ActionString VARCHAR(1000);
   SET N = now();
   SET ActionString = '';

   IF NEW.TranslatorID <> OLD.TranslatorID THEN
     SET ActionString = CONCAT(ActionString, 'TranslatorID(', OLD.TranslatorID, ' -> ', NEW.TranslatorID, ') ');
   END IF;

   IF NEW.StartDate <> OLD.StartDate THEN
     SET ActionString = CONCAT(ActionString, 'StartDate(', OLD.StartDate, ' -> ', NEW.StartDate, ') ');
   END IF;

   IF NEW.DueDate <> OLD.DueDate THEN
     SET ActionString = CONCAT(ActionString, 'DueDate(', OLD.DueDate, ' -> ', NEW.DueDate, ') ');
   END IF;

   IF NEW.EndDate <> OLD.EndDate THEN
     SET ActionString = CONCAT(ActionString, 'EndDate(', OLD.EndDate, ' -> ', NEW.EndDate, ') ');
   END IF;

   IF NEW.Notes <> OLD.Notes THEN
     SET ActionString = CONCAT(ActionString, 'Notes(', OLD.Notes, ' -> ', NEW.Notes, ') ');
   END IF;

   INSERT INTO TranslationHistory (TranslationID, Date, Action)
   VALUES (NEW.ID, N, ActionString);
END;

我不太喜欢它，因为它太长，乏味和重复，我确信它不是很好的SQL。我想要一个DRYer的方法来做到这一点。有没有办法在不必手动指定每列的详细信息的情况下执行此操作？

Answer 1

你可以把每个代码块都包装成一个函数，但是主程序中的代码不会比重构更少：

IF NEW.TranslatorID <> OLD.TranslatorID THEN
    SET ActionString = CONCAT(ActionString, 'TranslatorID(', OLD.TranslatorID, ' -> ', NEW.TranslatorID, ') ');
END IF;

进入这个：

SET ActionString = if(NEW.TranslatorID = OLD.TranslatorID, ActionString, CONCAT(ActionString, 'TranslatorID(', OLD.TranslatorID, ' -> ', NEW.TranslatorID, ') '));

有没有办法重构这个MySQL历史触发器？

1 个答案: