API Pagination done right. Pager API is a library to help you add meta information and the adequate header with pagination information based on the JSON API standard for your Rails app.

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pager_api depends on Pagy, Kaminari, WillPaginate to handle pagination. You need to add one of these gems to your Gemfile before the pager_api gem:

# gem 'will_paginate'
# gem 'kaminari'
# gem 'pagy'
gem 'pager_api'

And then execute:

% bundle

This step is totally optional

The gem comes with an installer for you to configure it, for example to switch between pagination handlers or whether or not to include the Link header or meta information. To install it you just need to run:

% rails g pager_api:install

This will create a file under the initializers directory called pager_api.rb. You can easily configure it there to meet your needs.

By default pager_api uses Pagy. Configure the pager_api.rb initializer in order to use WillPaginate or Kaminari.

We highly recommend you use Active Model Serializers for rendering your JSON responses

Currently the pager-api gem needs some configuration to work nice with Active Model Serializers, just add a file under config/initializers on your rails project:

% touch config/initializers/active_model_serializers.rb

And a this line:

ActiveModelSerializers.config.adapter = :json

Or even

ActiveModelSerializers.config.adapter = :json_api

In the controller where you are providing a paginated collection, you may have something like this:

class UsersController < ApplicationController
  def index
    users = User.page(params[:page]).per(15)

    render json: users,
           meta: {
             pagination: {
               per_page: 15,
               total_pages: 10,
               total_objects: 150
             }
           }
  end
end

With pager_api it is really easy to achieve the above by:

class UsersController < ApplicationController
  def index
    # You can have any scope for the User class in this case
    # You can even send the paginated collection
    paginate User.unscoped, per_page: 15
  end
end

This will output a json object like:

{
    "users": [
    	...
    ],
    "meta": {
        "pagination": {
            "per_page": 15,
            "total_pages": 1,
            "total_objects": 15,
            "links": {
                "first": "/api/users?page=1",
                "last": "/api/users?page=1"
            }
        }
    }
}

As you can see, the pagination metadata also includes the links information for the first and last page, but it will also create the next and the prev keys when necessary.

By default it will also include a Link header with the following information:

# Link: <http://example.com/api/v1/users?page="2">; rel="next",
# <http://example.com/api/v1/users?page="5">; rel="last",
# <http://example.com/api/v1/users?page="1">; rel="first",
# <http://example.com/api/v1/users?page="1">; rel="prev",

The header will be created with the corresponding first, last, prev and next links.

Have a bug or a feature request? Please open a new issue. Before opening any issue, please search for existing issues.

Please submit all pull requests against a separate branch. Although pager_api does not have tests yet, be a nice guy and add some for your feature. We'll be working hard to add them too.

In case you are wondering what to attack, we have a milestone with the version to work, some fixes and refactors. Feel free to start one.

Thanks!

Abraham Kuri

• http://twitter.com/kurenn
• http://github.com/kurenn
• http://klout.com/#/kurenn

Code and documentation copyright 2015 Icalia Labs. Code released under the MIT license.