app/controllers/concerns/pagination_methods.rb

   1 module PaginationMethods
   2   extend ActiveSupport::Concern
   3
   4   private
   5
   6   ##
   7   # limit selected items to one page, get ids of first item before/after the page
   8   def get_page_items(items, includes: [], limit: 20, cursor_column: :id)
   9     param! :before, Integer, :min => 0
  10     param! :after, Integer, :min => 0
  11
  12     qualified_cursor_column = "#{items.table_name}.#{cursor_column}"
  13     page_items = if params[:before]
  14                    items.where("#{qualified_cursor_column} < ?", params[:before]).order(cursor_column => :desc)
  15                  elsif params[:after]
  16                    items.where("#{qualified_cursor_column} > ?", params[:after]).order(cursor_column => :asc)
  17                  else
  18                    items.order(cursor_column => :desc)
  19                  end
  20
  21     page_items = page_items.limit(limit)
  22     page_items = page_items.includes(includes)
  23     page_items = page_items.sort.reverse
  24
  25     newer_items_cursor = page_items.first&.send cursor_column
  26     older_items_cursor = page_items.last&.send cursor_column
  27
  28     [
  29       page_items,
  30       (newer_items_cursor if page_items.any? && items.exists?(["#{qualified_cursor_column} > ?", newer_items_cursor])),
  31       (older_items_cursor if page_items.any? && items.exists?(["#{qualified_cursor_column} < ?", older_items_cursor]))
  32     ]
  33   end
  34 end