Rails 4 order by virtual attribute

问题:

I have a Product model which has name and description columns in the database.

I also have a Product.search_results_for(query), where query is a string like "Green Apple".

I need to return an ActiveRecord::Relation of the results ordered by which is the best hit. Currently, I'm setting a search_result_value to each product. search_result_value IS NOT a column in the database, and I don't want it to be.

So in essence, I have an ActiveRecord::Relation of Products that I need to order by search_result_value without changing it to an array, which is an instance variable that isn't stored in the database. How can I do this?

Something like this:

Product.order(:search_result_value)

回答1:

If you do not put the value in a column or express the logic in search_result_value in pure SQL, then you’ll have to load all Products into memory and then sort them in Ruby using sort_by:

Product.all.to_a.sort_by(&:search_result_value)