ruby-on-rails – 如何让Rails加载计数？

您可以非常聪明地使用原始模型与set_table_name结合使用子类：sql_view_name来保留对象上的所有原始方法,甚至可能还包含其中一些关联.

例如,我们要在你的例子中添加“Post.has_many：comments”,就像在@ Zubin的上面的答案一样;那么人们可能会做到：

class CreatePostsWithCommentsCountsView < ActiveRecord::Migration
      def self.up
        #Create SQL View called posts_with_comments_counts which maps over 
        # select posts.*,count(comments.id) as comments_count from posts 
        #   left outer join comments on comments.post_id = posts.id 
        #   group by posts.id
        # (As zubin pointed out above.) 
        #*Except* this is in SQL so perhaps we'll be able to do further 
        # reducing queries against it *as though it were any other table.*
      end    
   end

   class PostWithCommentsCount < Post         #Here there be cleverness.
                                              #The class definition sets up PWCC 
                                              # with all the regular methods of 
                                              # Post (pointing to the posts table
                                              # due to Rails' STI facility.)

    set_table_name :posts_with_comment_counts #But then we point it to the 
                                              # SQL view instead.
                                              #If you don't really care about
                                              # the methods of Post being in PWCC
                                              # then you could just make it a 
                                              # normal subclass of AR::Base.
   end

   PostWithCommentsCount.all(:include => :user)  #Obviously,this sort of "upward
     # looking" include is best used in big lists like "latest posts" rather than
     # "These posts for this user." But hopefully it illustrates the improved 
     # activerecordiness of this style of solution.
   PostWithCommentsCount.all(:include => :comments) #And I'm pretty sure you 
     # should be able to do this without issue as well. And it _should_ only be 
     # the two queries.