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Simple Pagination Concern for Ruby on Rails

This is a reusable pagination concern that provides a simple solution for pagination in a Ruby on Rails application.

Some of the code comes from Jonathan Allard who originally shared it here. However, I came across issues with the original code when specifying which page should be displayed. Rails would change up the order of the records resulting in incorrect ordering when paging through results – essentially breaking the pagination functionality. Adding in order_by and order_direction resolves the issue and also adds ordering functionality to the concern.

Here is the working code:

# app/controllers/concerns/pagination.rb

module Pagination
  extend ActiveSupport::Concern

  def default_per_page
    25
  end

  def page_num
    params.fetch(:page, 1).to_i
  end

  def per_page
    params.fetch(:per_page, 25).to_i
  end

  def paginate_offset
    (page_num - 1) * per_page
  end
  
  def order_by
  	params.fetch(:order_by, :id)
  end
  
  def order_direction
  	params.fetch(:order_direction, :asc)
  end

  def paginate
    ->(it) { it.limit(per_page).offset(paginate_offset).order("#{order_by}": order_direction) }
  end
end

Include it in your ApplicationController to make it available from any controller.

ActionController::Base
  include Pagination
end

It can then be used like this in your controllers:

def index
  records = Record.all
  records.then(&paginate)
end

In this example the default results per page is set to 25, however, this can be modified in the code or a per_page parameter can be passed to override the default.

GET /records?page=&per_page=100

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