application_record.rb

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true

  # Universal replacement for MySQL's ORDER BY FIELD(name, •values)
  def self.order_by_field(field, values)
    ordering_table_id = SecureRandom.urlsafe_base64

    ordering_table_rows = values.map.with_index { |value, index| "(#{value},#{index + 1})" }

    joins(
      <<-SQL
        INNER JOIN (VALUES #{ordering_table_rows.join(',')}) AS "ordering_table_#{ordering_table_id}" ("#{field}", "ordering")
        ON "#{table_name}"."#{field}" = "ordering_table_#{ordering_table_id}"."#{field}"
      SQL
    ).order("\"ordering_table_#{ordering_table_id}\".\"ordering\"")
  end
end