ruby-on-rails - 按 has_many 模型大小查找

Question

我正在开发 Rails 2.3.8 Ruby 1.8.7 和 PostgreSQL。

当我想搜索小于特定大小的模型时，如何编写查找条件？

例如，我想搜索少于 5 条评论的主题。

class Topic < ActiveRecord::Base
     has_many :comments
end

class Comment < ActiveRecord::Base
     belongs_to :topic
end

Topic.find(:all,:include => :comments, :conditions => [(which has less than 5 comments)])

Answer 1

这会解决你的问题吗？

Topic.find(:all, :select => 'topics.*, count(comments.id) AS comment_count', :joins => 'INNER JOIN comments ON comments.topic_id = topics.id', :group => 'comments .topic_id HAVING count(comments.topic_id) < 5' )