更新后触发无效缓存

Question

我试图编写触发器来使我的故事数据库的字索引无效。然而，我似乎无法弄清楚在索引操作过程中如何停止触发器再次触发。我知道我需要放置一条if语句来停止更新，但我似乎无法弄清楚它应该是什么样子。

CREATE TRIGGER trMarkStoryForReindex BEFORE UPDATE ON Chapters 
    FOR EACH ROW BEGIN 

    -- any update to any chapter invalidates the index for the whole story 
    -- we could just periodically flush the story index, but this way is 
    -- better. 
    SET New.isIndexed = FALSE; 
    -- delete the index for that story 
    -- It will get rebuilt in at most 15 minutes 
    DELETE FROM freq WHERE storyid = NEW.StoryId; 
END; 

我基本上只想触发器只有在触发器的update语句中没有设置isIndexed时才触发。

我的数据模型看起来像这样：

章

• ID
• isIndexed
• StoryId

频率

• 字
• storyid

Answer 1

这里是我的解决方案建议。我已经在SQL小提琴进行了测试，它似乎工作：

-- Database setup 
create table chapters (
    id int unsigned not null auto_increment primary key, 
    isIndexed boolean default false, 
    storyId int not null, 
    index idx_storyId(storyId) 
); 

create table freq (
    word varchar(50), 
    storyId int not null, 
    index idx_storyId(storyId) 
); 

delimiter // 
create trigger bi_chapters before update on chapters 
for each row 
begin 
    if new.isIndexed = false then 
    delete from freq where storyId = new.storyId; 
    end if; 
end // 
delimiter ; 

insert into freq(word, storyId) 
values ('one', 1), ('two', 1), ('three', 2); 

insert into chapters(isIndexed, storyId) 
values (true, 1), (true, 2); 

当你（更新chapters之前）选择freq的值，你会得到：

select * from chapters; 

| id | isIndexed | storyId | 
|----|-----------|---------| 
| 1 |  false |  1 | 
| 2 |  true |  2 | 

select * from freq; 

| word | storyId | 
|-------|---------| 
| one |  1 | 
| two |  1 | 
| three |  2 | 

现在，做一个update到章节，从select从freq再次：

update chapters 
    set isIndexed = false 
    where storyId = 1; 
select * from freq; 

| word | storyId | 
|-------|---------| 
| three |  2 | 

我做的唯一的修改是if块检查新行是否更新为false。如果我已经正确理解你的问题，这将做你所需要的。

• SQL fiddle example