Rails的運行重複查詢

Question

我的應用程序檢索一組的每個職位的標籤，但由於某種原因它正在運行重複查詢：

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

：

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 

，以保持它的簡單我在視圖頁面代碼

這裏是PostsHelper我的print_tags代碼：

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 

我不明白的是爲什麼它第1W運行一個查詢沒有order_by，然後用它運行查詢。性能還不錯還有，但是如果它真的在爲每個帖子運行兩個查詢，那麼它可能會變得非常快。

Answer 1

嘗試預先加載您的標籤關聯：

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

見Eager Loading Associations