Paginate Active Record sets at variable speeds
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README.md

Geared Pagination

Most pagination schemes use a fixed page size. Page 1 returns as many elements as page 2. But that's frequently not the most sensible way to page through a large recordset when you care about serving the initial request as quickly as possible. This is particularly the case when using the pagination scheme in combination with an infinite scrolling UI.

Geared Pagination allows you to define different ratios. By default, we will return 15 elements on page 1, 30 on page 2, 50 on page 3, and 100 from page 4 and forward. This has proven to be a very sensible set of ratios for much of the Basecamp UIs. But you can of course tweak the ratios, use fewer, or even none at all, if a certain page calls for a fixed-rate scheme.

On JSON actions that set a page, we'll also automatically set Link and X-Total-Count headers for APIs to be able to page through a recordset.

Example

class MessagesController < ApplicationController
  def index
    set_page_and_extract_portion_from Message.order(created_at: :desc)
  end
end

# app/views/messages/index.html.erb

Showing page <%= @page.number %> of <%= @page.recordset.page_count %> (<%= @page.recordset.records_count %> total messages):

<%= render @page.records %>

<% if @page.last? %>
  No more pages!
<% else %> 
  <%= link_to "Next page", messages_path(page: @page.next_number) %>
<% end %>

Caching

To account for the current page in fragment caches, include the @page directly. That includes the current page number and gear ratios.

Fragment caching a message's comments:

<% cache [ @message, @page ] do %>
  <%= render @page.records %>
<% end %>

NOTE: The page does not include cache keys for all the records. That would require loading all the records, defeating the purpose of using the cache. Use a parent record, like a message that's touched when new comments are posted, as the cache key instead.

ETags

When a controller action sets an ETag and uses geared pagination, the current page and gear ratios are automatically included in the ETag.

License

Geared Pagination is released under the MIT License.