A generic data table class to support rendering DataTables from remote. Most of the code from RailsCasts #340 (http://railscasts.com/episodes/340-datatables). Inherit this class and override the columns, records and data methods.

generic_datatable.rb

class GenericDatatable
  delegate :params, :h, :link_to, :raw, to: :@view

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

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

private

  # override this method in child class
  def data
  end

  # override this method in child class
  def records
  end

  # override this method in child class
  def columns
    %w[]
  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 sort_column
    columns[params[:iSortCol_0].to_i]
  end

  def sort_direction
    params[:sSortDir_0] == "desc" ? "desc" : "asc"
  end

  def column_search
    search_string = []
    params.keys.map {|x| x if params[x].present? and x.include? "sSearch_"}.compact.each do |search|
      index = search.split("_").last.to_i
      search_string << "#{columns[index]} ilike '%#{params[search]}%'"
    end
    search_string.join(' and ')
  end

end

items_datatable.rb

class ItemsDatatable < GenericDatatable

private

  def data
    records.map do |item|
      [ item.id,
        link_to(item.code, item),
        item.name,
        item.category,
        item.location,
        item.vendor
      ]
    end
  end

  def records
    @records ||= Item.all
    items = @records.order("#{sort_column} #{sort_direction}")
    items = items.page(page).per_page(per_page)
    items = items.where(column_search).references(:items)
    if params[:sSearch].present?
      items = items.where("name ilike :search or category ilike :search", search: "%#{params[:sSearch]}%")
    end
    items
  end

  def columns
    %w[items.id items.code items.name items.category items.location items.vendor]
  end

end