I was a bit surprised to see mongoid drop pagination support in 2.0.2 (here and here). It got some people confused (see #983). In a project that uses will_paginate, this results in very slow large queries, but no other breakage. It looks like Mongoid did the right thing though – their implementation was messy and other extensions do a much cleaner job.

Here’s what I had to do to switch from will_paginate to kaminari. The latter works well with Mongoid 2.0.2.

Replace will_paginate with kaminari in Gemfile.

1. gem "kaminari", "0.12.4"

Replace all calls to .paginate :page => params[:page], :per_page => 20 with the kaminari methods.

1. Model.desc(:created_at).page(params[:page]).per(20)

There may be some loading order issues since kaminari injects methods on load. For delayed jobs I had to do the following in the initializer (see #10).

1. Delayed::Job.send(:include, Kaminari::MongoidExtension::Document)

If you have a shared pagination block (eg. app/views/shared/pagination/_pagination.html.haml) change it to use kaminari layouts.

1. #pagination
2. = paginate items

There’s a pull request #140 for page_entries_info, it looks like it still has a couple of issues. We’ve added config/initializers/kaminari.rb for now.

If you’re paginating arrays you can inject a few methods into a paged result set on-the-fly to make it play nice.

1. @paged_result_set.instance_eval <<-EVAL
2.   def current_page
3.     #{params[:page] || 1}
4.   end
5.   def num_pages
6.     count
7.   end
8.   def limit_value                                                                               
9.     20
10.   end
11. EVAL