Question

I have two models

Post
  has_many :comments

Comment
  belongs_to :post

When I want display a list of posts and it’s comment count. I usually include comments in the post like this .

Post.find(:all,:include => :comments)

To display a number of comment for post.

post.comments.size

Can I create a has_many relation which return count of comments ?

 has_one :comments_count

Can I include this relationship like this ?

Post.find(:all,:include => :comments_count)

Answer 1

Rails has a counter cache which will automatically update a columns value based on the count of associated items. This will allow you to include the count when you return the posts object. Just add it to the belongs_to on comment.

Comment
  belongs_to :post, :counter_cache => true

You’ll need to add a new integer column to posts for the counter:

class AddCounterCacheToPosts < ActiveRecord::Migration
  def self.up
    add_column :posts, :comments_count, :integer
  end
end