Question

我的应用会检索每个帖子的一组标签，但由于某种原因，它会运行重复的查询：

Post Load (0.2ms)  SELECT  `posts`.* FROM `posts`  WHERE `posts`.`user_id` = 1                      
Tag Load (0.2ms)  SELECT `tags`.* FROM `tags` INNER JOIN `post_tags` ON `tags`.`id` = `post_tags`.`tag_id` WHERE `post_tags`.`post_id` = 107
Tag Load (0.3ms)  SELECT `tags`.* FROM `tags` INNER JOIN `post_tags` ON `tags`.`id` = `post_tags`.`tag_id` WHERE `post_tags`.`post_id` = 107  ORDER BY post_tags.created_at
Tag Load (0.1ms)  SELECT `tags`.* FROM `tags` INNER JOIN `post_tags` ON `tags`.`id` = `post_tags`.`tag_id` WHERE `post_tags`.`post_id` = 106
Tag Load (0.2ms)  SELECT `tags`.* FROM `tags` INNER JOIN `post_tags` ON `tags`.`id` = `post_tags`.`tag_id` WHERE `post_tags`.`post_id` = 106  ORDER BY post_tags.created_at
Tag Load (0.2ms)  SELECT `tags`.* FROM `tags` INNER JOIN `post_tags` ON `tags`.`id` = `post_tags`.`tag_id` WHERE `post_tags`.`post_id` = 105
Tag Load (0.2ms)  SELECT `tags`.* FROM `tags` INNER JOIN `post_tags` ON `tags`.`id` = `post_tags`.`tag_id` WHERE `post_tags`.`post_id` = 105  ORDER BY post_tags.created_at

让我的代码在视图页面中保持简单：

@posts.each do |post| 
    # code/html to print out post here
    print_tags(post.tags.order('created_at desc'))
end

这是我在PostsHelper中的print_tags代码：

def print_tags(tags)

    returnStr = ""
    tags.each do |tag| 
        returnStr += "<span class='tags'><a href='/users/#{@user.id}/tags/#{tag.tag_name.gsub(' ', '-')}'>#{tag.tag_name}</a></span>" 
    end

    returnStr
end

我不明白为什么它在没有order_by的情况下首先运行查询，然后用它运行查询。性能还不错尚未，但如果它确实为每个帖子运行了两个查询，那么这可能会很快变得难看。

Answer 1

尝试急切加载您的代码关联：

@posts.includes(:tags).each do |post| 
  # do something with `post.tags`
end

请参阅Eager Loading Associations

Rails运行重复的查询

1 个答案: