app/controllers/concerns/pagination_methods.rb

   1 # frozen_string_literal: true
   2
   3 module PaginationMethods
   4   extend ActiveSupport::Concern
   5
   6   Paginator = Struct.new(:items, :newer_items_cursor, :older_items_cursor)
   7
   8   private
   9
  10   ##
  11   # limit selected items to one page, get ids of first item before/after the page
  12   def get_page_items(items, includes: [], limit: 20, cursor_column: :id)
  13     param! :before, Integer, :min => 0
  14     param! :after, Integer, :min => 0
  15
  16     qualified_cursor_column = "#{items.table_name}.#{cursor_column}"
  17     page_items = if params[:before]
  18                    items.where("#{qualified_cursor_column} < ?", params[:before]).reorder(cursor_column => :desc)
  19                  elsif params[:after]
  20                    items.where("#{qualified_cursor_column} > ?", params[:after]).reorder(cursor_column => :asc)
  21                  else
  22                    items.reorder(cursor_column => :desc)
  23                  end
  24
  25     page_items = page_items.limit(limit)
  26     page_items = page_items.includes(includes)
  27     page_items = page_items.sort.reverse
  28
  29     newer_items_cursor = page_items.first&.send cursor_column
  30     older_items_cursor = page_items.last&.send cursor_column
  31
  32     Paginator.new(
  33       :items => page_items,
  34       :newer_items_cursor => (newer_items_cursor if page_items.any? && items.exists?(["#{qualified_cursor_column} > ?", newer_items_cursor])),
  35       :older_items_cursor => (older_items_cursor if page_items.any? && items.exists?(["#{qualified_cursor_column} < ?", older_items_cursor]))
  36     )
  37   end
  38 end