JSONAPI

sortable.rb

# app/models/concerns/sortable.rb
module Sortable
  extend ActiveSupport::Concern

  included do
    # Model.smart_sort("attribute_a,+attribute_b,-attribute_c")
    # is equivalent to
    # Model.order(attribute_a).order(attribute_b: :asc).order(attribute_c: :desc)
    scope :smart_sort, -> (sort) {
      scope = self.all
      String(sort).split(',').each do |attribute|

        # ASC or DESC?
        first_char = attribute[0]
        direction = :asc
        if first_char == '-'
          direction = :desc
          attribute = attribute[1..-1]
        elsif first_char == '+'
          attribute = attribute[1..-1]
        end

        # Is it an authorized attribute?
        if self.sortable_attributes.include? attribute

          # Is it a "association_name.column_name" pattern?
          association_name, column = attribute.split('.')
          unless column
            column = association_name
            association_name = nil
          end

          # Lookup for association model (which is `self` when no association given)
          if association_name
            association = self.reflect_on_all_associations.select{ |association| association.name == association_name.to_sym }.first
            if association
              scope = scope.joins(association_name.to_sym)
              model = association.class_name.constantize
            else
              raise ActionController::BadRequest, "#{self} misses #{association_name} association."
            end
          else
            model = self
          end

          if column_reflection = model.columns_hash[column]
            if column_reflection.type == :string
              scope = scope.order("UNACCENT(LOWER(\"#{model.table_name}\".\"#{column}\")) #{direction.upcase}")
            else
              scope = scope.order("\"#{model.table_name}\".\"#{column}\" #{direction.upcase}")
            end
          else
            # SQL computed / aliased attribute, do not prefix with table name
            scope = scope.order("#{attribute} #{direction.upcase}")
          end
        else
          raise ActionController::BadRequest, "#{self} sortable attributes do not include #{attribute}."
        end
      end
      scope
    }
  end

  module ClassMethods
    attr_accessor :sortable_attributes
    def sortable *attributes
      self.sortable_attributes = attributes.map(&:to_s)
    end
  end
end