datatable superclass that handles server side multi-column searching and sorting

datatable superclass

# derived from http://railscasts.com/episodes/340-datatables
# handles server side multi-column searching and sorting

class Datatable
  delegate :params, :h, :raw, :link_to, :number_to_currency, to: :@view

  def initialize(klass,view)
    @klass = klass
    @view = view
  end

  def as_json(options = {})
    {
      sEcho: params[:sEcho].to_i,
      iTotalRecords: @klass.count,
      iTotalDisplayRecords: items.total_entries,
      aaData: data
    }
  end

private

  def data
    []
  end

  def items
    @items ||= fetch_items
  end

  def fetch_items
    items = filtered_list
    items = selected_columns(items)
    items = items.order(sort_order)
    items = items.page(page).per_page(per_page)
    if params[:sSearch].present?
      items = items.where(quick_search)
    end
    items
  end

  def filtered_list
    @klass.scoped
  end

  def selected_columns items
    items
  end
  
  def quick_search
    search_for = params[:sSearch].split(' ')
    terms = {}
    which_one = -1 
    criteria = search_for.inject([]) do |criteria,atom|
      which_one += 1
      terms["search#{which_one}".to_sym] = "%#{atom}%"
      criteria << "(#{search_cols.map{|col| "#{col} like :search#{which_one}"}.join(' or ')})"
    end.join(' and ')
    [criteria, terms]
  end

  def page
    params[:iDisplayStart].to_i/per_page + 1
  end

  def per_page
    params[:iDisplayLength].to_i > 0 ? params[:iDisplayLength].to_i : 10
  end

  def columns
    []
  end

  def sort_order
    colnum = 0
    sort_by = []
    while true
      break if !sorted?(colnum)
      sort_by << "#{sort_column(colnum)} #{sort_direction(colnum)}"
      colnum += 1
    end
    sort_by.join(", ")
  end

  def sorted? index=0
    !params["iSortCol_#{index}"].nil?
  end

  def sort_column index=0
    index = "iSortCol_#{index}"
    columns[params[index].to_i]
  end

  def sort_direction index=0
    index = "sSortDir_#{index}"
    params[index] == "desc" ? "desc" : "asc"
  end
end

Thank you for sharing this! It is very useful.

Thank you for sharing! What should be passed to the klass param?

I'w think that the klass param should receive something like Product, User, Category...