How do you order by a custom model method that has no attribute in SQL?

Question

Previously I ordered my posts as this:

@posts = Post.find(:all, :order => \"created_at DESC\")

But now I want to replace created_at

Answer 1

This is a bit more complicated than what I like but this I like to keep my sort to stay as a active record model so its bit more complicated than just

Post.all.sort_by {|post| post.custom_method }

what I do is:

ids = Post.all.sort_by {|post| post.custom_method }.map(&:ids)
Post.for_ids_with_order(ids)

this is a custom scope in the Post model

#app/models/post.rb
class Post < ApplicationRecord
  ...
    scope :for_ids_with_order, ->(ids) {
    order = sanitize_sql_array(
      ["position(id::text in ?)", ids.join(',')]
    )
    where(:id => ids).order(order)
  }

  ...
end

I hope that this help