Rails：将这些请求转换为 counter_cache 的最佳方法

Question

每个页面加载我都有几个这样的请求：

SELECT COUNT(*) FROM `impressions` WHERE `impressions`.`impressionable_id` IN (229) AND `impressions`.`impressionable_type` = 'Document' AND (YEAR(created_at) = 2013 && MONTH(created_at) = 8 && DAY(created_at) = 12)
SELECT COUNT(*) FROM `impressions` WHERE `impressions`.`impressionable_id` IN (229) AND `impressions`.`impressionable_type` = 'Document' AND (YEAR(created_at) = 2013 && MONTH(created_at) = 8 && DAY(created_at) = 13)
SELECT COUNT(*) FROM `impressions` WHERE `impressions`.`impressionable_id` IN (229) AND `impressions`.`impressionable_type` = 'Document' AND (YEAR(created_at) = 2013 && MONTH(created_at) = 8 && DAY(created_at) = 14)
SELECT COUNT(*) FROM `impressions` WHERE `impressions`.`impressionable_id` IN (229) AND `impressions`.`impressionable_type` = 'Document' AND (YEAR(created_at) = 2013 && MONTH(created_at) = 8 && DAY(created_at) = 15)

我想减少服务器上的负载，因此我试图将其转换为counter_cache 解决方案。由于我试图计算复杂的关系，我需要一些帮助来设计它。这是获取计数的查询：

Impression.where(:impressionable_id => component.publications.where(:document_id => document).first.id).count

我应该将counter_cache 列放在哪里？我应该如何编写迁移？ Component 和 Document 通过 Publications 处于 has_many 关系中。

Answer 1

假设展示次数是针对Publication，并且展示次数是按每天分组的。

您可以创建PublicationImpression 模型来作为每个Publication 每天印象数的计数器。

class CreatePublicationImpressions < ActiveRecord::Migration
  def self.up
    create_table :publication_impressions, :id => false do |t|
      t.integer :impressions, :default => 0
      t.datetime :date
      t.references :publication

      t.timestamps
    end
  end

  def self.down
    drop_table :publication_impressions
  end
end