Rails powered API - resources ordering by URL params (ie /resources?order=created_at.desc)

order_by_params_helper.rb

# (c) 2014 Lukas Dolezal (lukas@dolezalu.cz)
# MIT licence

# include in your base controller (ApplicationController):
# include OrderByParamsHelper
module OrderByParamsHelper

  # use in controller:
  # @resources = order_by_params(@resources, params[:order], :created_at)
  #
  # call your URL:
  # /resources?order=created_at.desc
  def order_by_params(resources, order_param, *allowed_fields)
    return resources if order_param.nil?

    order_fields =
    order_param
    .split(',')
    .map{|o| o.split('.')}
    .select{|o|
      allowed_fields.include?(o[0].downcase.to_sym) &&
      [:desc, :asc].include?(o[1].downcase.to_sym)
    }
    .map{|o| "#{o[0].downcase} #{o[1].downcase}"}

    if order_fields.empty?
      resources
    else
      resources.order(order_fields.join(','))
    end
  end

end