has_many count column

[glennfu]

I have a User, which has_many :posts. I'd love to have a column that showed the # of posts, so I could sort my Users by the ones with the most posts. Is this possible?

[glennfu]

I can do this manually, with Postgres support, by running:

    @users = User.select("(select COUNT(posts.id) from posts where posts.user_id = users.id) 
        AS posts_count, users.#{User.column_names.join(",users.")}").
        order("posts_count DESC").limit(30)

[bbenezech]

I would use a counter cache column to do that. Please use the mailing-list for assistance.