Question

我在一个循环中有一个AR对象的集合，可能会多次运行，所以我想在每次迭代结束时清空集合。

最有效的方法是什么？

修改1

以下是我使用.clear时会发生什么的示例：

1.9.3p392 :039 > t = w.tags
 => [#<Tag id: 32451, name: "c++", num_questions: 180854, created_at: "2013-02-25 07:55:55", updated_at: "2013-02-25 07:55:55">, #<Tag id: 32452, name: "performance", num_questions: 28543, created_at: "2013-02-25 07:55:55", updated_at: "2013-02-25 07:55:55">, #<Tag id: 32453, name: "optimization", num_questions: 10021, created_at: "2013-02-25 07:55:55", updated_at: "2013-02-25 07:55:55">, #<Tag id: 32454, name: "language-agnostic", num_questions: 5942, created_at: "2013-02-25 07:55:55", updated_at: "2013-02-25 07:55:55">, #<Tag id: 32455, name: "branch-prediction", num_questions: 28, created_at: "2013-02-25 07:55:55", updated_at: "2013-02-25 07:55:55">, #<Tag id: 32456, name: "books", num_questions: 2667, created_at: "2013-02-25 07:55:59", updated_at: "2013-02-25 07:55:59">, #<Tag id: 32457, name: "ebook", num_questions: 263, created_at: "2013-02-25 07:55:59", updated_at: "2013-02-25 07:55:59">, #<Tag id: 32458, name: "creative-commons", num_questions: 62, created_at: "2013-02-25 07:55:59", updated_at: "2013-02-25 07:55:59">, #<Tag id: 32459, name: "json", num_questions: 39746, created_at: "2013-02-25 07:56:03", updated_at: "2013-02-25 07:56:03">, #<Tag id: 32460, name: "content-type", num_questions: 874, created_at: "2013-02-25 07:56:03", updated_at: "2013-02-25 07:56:03">] 
1.9.3p392 :040 > t.clear
   (19.0ms)  BEGIN
   (85.2ms)  DELETE FROM "questions_tags" WHERE "questions_tags"."question_id" = 10053 AND "questions_tags"."tag_id" IN (32451, 32452, 32453, 32454, 32455, 32456, 32457, 32458, 32459, 32460)
   (36.5ms)  COMMIT
 => [] 
1.9.3p392 :041 > t
 => [] 
1.9.3p392 :042 > t
 => [] 
1.9.3p392 :043 > w.tags
 => []

Answer 1

The builtin method：

 your_array.clear

Answer 2

请查看Rails doc on associations。 clear方法不是Array#clear，它被Rails覆盖。

我只是复制关联中的元素，这将确保关联将延迟加载，例如：

tags = w.tags.collect{|t| t}
tags.clear

清除ActiveRecord对象集合的最有效方法是什么？

2 个答案: