has_many通过：关系计数

Question

I was hoping someone could help me with this, been trying to figure it out for a week now, I found a lot of examples, but as I'm new to rails I guess I keep making a mistake somewhere and I just cant find a right solution for my case. So I have:

class Blog < ActiveRecord::Base
   attr_accessible :name, :subject_id, :created_at
   has_many :blogs_messages
   has_many :messages, through: :blogs_messages
end

class Message < ActiveRecord::Base
   attr_accessible :title, :body, :created_at
   has_many :blogs_messages
   has_many :blogs, through: :blogs_messages
end

class BlogsMessages < ActiveRecord::Base
  attr_accessible :message_id, :blog_id
  belongs_to :blog
  belongs_to :message
end

Messages live in different Blogs(like Pink Blog, Green Blog, Maroon Blog etc), and Blogs live in Subjects (Dark Colors, Bright Colors etc) Subjects have many Blogs, but Blogs can belong only to one Subject.

BlogsMessages is the connection between Messages and Blogs what im trying to do is to show: top 3 Blogs (by amount of messages in them) within one Subject

so eg when I want to choose Subject Dark Colors it will show me:

    1.Maroon Blog: 46 messages
    2.Grey Blog: 13 messages
    3.Purple Blog: 12 messages 

(There are 8 Blogs altogether in Subject Dark Colors.)

Could someone please help me with this, or at least point me in the right direction how to make it all work?

Update:

in my Blogs_controller now i have:

@blogs = Blog.joins(:blogs_messages => :message).select('blogs.*, COUNT(messages.id) AS message_count').group('blog_id').order('COUNT(messages.id) DESC').limit(3)

in my blogs view:

    <% @blogs.each do |blog| %>
      <li><%= blog.name %>:  messages</li>
    <% end %>

Answer 1

I'm not sure this can work because I can't test it but it may help you:

 Blog.where(subject_id: subject.id)
      .joins(:blogs_messages => :message)
      .select('blogs.*, COUNT(messages.id) AS message_count')
      .group(:blog_id)
      .order('message_count DESC')
      .limit(3)

Also, in the view you could access to the new virtual attribute message_count :

 <% @blogs.each do |blog| %>
   <li><%= blog.name %>: <%= blog.message_count %> messages</li>
 <% end %>