:counter_cache =>true 用于存储总和 [英] :counter_cache => true for storing sum

问题描述

我有users 和scores 表.以下是关联:

I have the table users and scores. Here are the associations:

belongs_to :user #score model
has_many :scores #user model

表 users 有名为 scores_count 的列.在此列中，我将所有值的总和存储在 scores 表中.

The table users has the column called scores_count. In this column I store the sum of all values in the table scores.

我想用这种方式将所有 scores 的总和存储在 scores_count::counter_cache =>真实

I wanted to use this way for storing the sum of all scores in the column scores_count: :counter_cache => true

但是 :counter_cache =>true 只保存表 scores 中的行数.是否有任何类似的方法来存储表 scores 中所有值的总和?还是这个任务要我自己来实现?

But :counter_cache => true saving only the count of rows in the table scores. Is there any similar method for storing the sum of all values from the table scores? Or this task I have to implement by myself?

推荐答案

没有.你必须自己实现它.计数器缓存仅用于存储关联记录的数量.您可以使用 Score 上的回调来实现它，以更新关联的 User.另请参阅如何在 rails 中缓存计算列?

No. You'll have to implement it yourself. Counter-cache is for storing the number of associated records only. You could implement it using a callback on Score to update the associated User. See also How can I cache a calculated column in rails?

此外，除非每次求和都有明显的性能问题，否则请避免使用这样的缓存.它只是很容易出错并过时的东西.如果你真的不需要它，那就不值得麻烦了.

Further, unless you have noticeable performance issues with summing each time, avoid using a cache like this. It's just something that can easily go wrong and get out-of-date. It's not worth the trouble if you don't really need it.

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