Move sorting and pagination logic at common place

application_controller.rb

  def paginated(resources, per_page=Settings.pagination.default)
    resources.page(params[:page]).per(per_page)
  end

  def sort_by_options(resources)
    resources.order("#{sort_column(resources.first.class)}  #{sort_direction}")
  end

  def sort_and_paginate(resources)
    paginated(sort_by_options(resources))
  end

  def sort_column(resource, default_column = "created_at")
     if resource.present? && resource != NilClass
      resource.column_names.include?(params[:sort]) ? params[:sort] : default_column
    else
      default_column
    end
  end

  def sort_direction
    %w[asc desc].include?(params[:direction]) ? params[:direction] : 'desc'
  end

dashboard_controller.rb

def index
  sort_and_paginate(Products.selling_fast)
end