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https://github.com/davidcelis/api-pagination

:page_facing_up: Link header pagination for Rails and Grape APIs.
https://github.com/davidcelis/api-pagination

api grape kaminari pagination rails ruby willpaginate

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:page_facing_up: Link header pagination for Rails and Grape APIs.

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# api-pagination



Paginate in your headers, not in your response body.

This follows the proposed [RFC-8288](https://tools.ietf.org/html/rfc8288) standard for Web linking.



## Installation



In your `Gemfile`:



```ruby

# Requires Rails (Rails-API is also supported), or Grape

# v0.10.0 or later. If you're on an earlier version of

# Grape, use api-pagination v3.0.2.

gem 'rails', '>= 3.0.0'

gem 'rails-api'

gem 'grape', '>= 0.10.0'



# Then choose your preferred paginator from the following:

gem 'pagy'

gem 'kaminari'

gem 'will_paginate'



# Finally...

gem 'api-pagination'

```



## Configuration (optional)



By default, api-pagination will detect whether you're using Pagy, Kaminari, or WillPaginate, and it will name headers appropriately. If you want to change any of the configurable settings, you may do so:



```ruby

ApiPagination.configure do |config|

  # If you have more than one gem included, you can choose a paginator.

  config.paginator = :kaminari # or :will_paginate



  # By default, this is set to 'Total'

  config.total_header = 'X-Total'



  # By default, this is set to 'Per-Page'

  config.per_page_header = 'X-Per-Page'



  # Optional: set this to add a header with the current page number.

  config.page_header = 'X-Page'



  # Optional: set this to add other response format. Useful with tools that define :jsonapi format

  config.response_formats = [:json, :xml, :jsonapi]



  # Optional: what parameter should be used to set the page option

  config.page_param = :page

  # or

  config.page_param do |params|

    params[:page][:number] if params[:page].is_a?(ActionController::Parameters)

  end



  # Optional: what parameter should be used to set the per page option

  config.per_page_param = :per_page

  # or

  config.per_page_param do |params|

    params[:page][:size] if params[:page].is_a?(ActionController::Parameters)

  end



  # Optional: Include the total and last_page link header

  # By default, this is set to true

  # Note: When using kaminari, this prevents the count call to the database

  config.include_total = false

end

```



### Pagy-specific configuration



Pagy does not have a built-in way to specify a maximum number of items per page, but `api-pagination` will check if you've set a `:max_per_page` variable. To configure this, you can use the following code somewhere in an initializer:



```ruby

Pagy::DEFAULT[:max_per_page] = 100

```



If left unconfigured, clients can request as many items per page as they wish, so it's highly recommended that you configure this.



## Rails



In your controller, provide a pageable collection to the `paginate` method. In its most convenient form, `paginate` simply mimics `render`:



```ruby

class MoviesController < ApplicationController

  # GET /movies

  def index

    movies = Movie.all # Movie.scoped if using ActiveRecord 3.x



    paginate json: movies

  end



  # GET /movies/:id/cast

  def cast

    actors = Movie.find(params[:id]).actors



    # Override how many Actors get returned. If unspecified,

    # params[:per_page] (which defaults to 25) will be used.

    paginate json: actors, per_page: 10

  end

end

```



This will pull your collection from the `json` or `xml` option, paginate it for you using `params[:page]` and `params[:per_page]`, render Link headers, and call `ActionController::Base#render` with whatever you passed to `paginate`. This should work well with [ActiveModel::Serializers](https://github.com/rails-api/active_model_serializers). However, if you need more control over what is done with your paginated collection, you can pass the collection directly to `paginate` to receive a paginated collection and have your headers set. Then, you can pass that paginated collection to a serializer or do whatever you want with it:



```ruby

class MoviesController < ApplicationController

  # GET /movies

  def index

    movies = paginate Movie.all



    render json: MoviesSerializer.new(movies)

  end



  # GET /movies/:id/cast

  def cast

    actors = paginate Movie.find(params[:id]).actors, per_page: 10



    render json: ActorsSerializer.new(actors)

  end

end

```



Note that the collection sent to `paginate` _must_ respond to your paginator's methods. This is typically fine unless you're dealing with a stock Array. For Kaminari, `Kaminari.paginate_array` will be called for you behind-the-scenes. For WillPaginate, you're out of luck unless you call `require 'will_paginate/array'` somewhere. Because this pollutes `Array`, it won't be done for you automatically. If you use Pagy, it doesn't matter, because Pagy doesn't care what you're paginating. It will just work, as long as the collection responds to `count`.



**NOTE:** In versions 4.4.0 and below, the `Rails::Pagination` module would end up included in `ActionController::Base` even if `ActionController::API` was defined. As of version 4.5.0, this is no longer the case. If for any reason your API controllers cannot easily changed be changed to inherit from `ActionController::API` instead, you can manually include the module:



```ruby

class API::ApplicationController < ActionController::Base

  include Rails::Pagination

end

```



## Grape



With Grape, `paginate` is used to declare that your endpoint takes a `:page` and `:per_page` param. You can also directly specify a `:max_per_page` that users aren't allowed to go over. Then, inside your API endpoint, it simply takes your collection:



```ruby

class MoviesAPI < Grape::API

  format :json



  desc 'Return a paginated set of movies'

  paginate

  get do

    # This method must take an ActiveRecord::Relation

    # or some equivalent pageable set.

    paginate Movie.all

  end



  route_param :id do

    desc "Return one movie's cast, paginated"

    # Override how many Actors get returned. If unspecified,

    # params[:per_page] (which defaults to 25) will be used.

    # There is no default for `max_per_page`.

    paginate per_page: 10, max_per_page: 200

    get :cast do

      paginate Movie.find(params[:id]).actors

    end



    desc "Return one movie's awards, paginated"

    # Enforce max_per_page value will add the alowed values

    # to the swagger docs, and cause grape to return an error

    # if outside that range

    paginate per_page: 10, max_per_page: 200, enforce_max_per_page: true

    get :awards do

      paginate Movie.find(params[:id]).awards

    end

  end

end

```



## Headers



Then `curl --include` to see your header-based pagination in action:



```bash

$ curl --include 'https://localhost:3000/movies?page=5'

HTTP/1.1 200 OK

Link: ; rel="first",

  ; rel="last",

  ; rel="next",

  ; rel="prev"

Total: 4321

Per-Page: 10

# ...

```



## A Note on Kaminari and WillPaginate



api-pagination requires either Kaminari or WillPaginate in order to function, but some users may find themselves in situations where their application includes both. For example, you may have included [ActiveAdmin][activeadmin] (which uses Kaminari for pagination) and WillPaginate to do your own pagination. While it's suggested that you remove one paginator gem or the other, if you're unable to do so, you _must_ configure api-pagination explicitly:



```ruby

ApiPagination.configure do |config|

  config.paginator = :will_paginate

end

```



If you don't do this, an annoying warning will print once your app starts seeing traffic. You should also configure Kaminari to use a different name for its `per_page` method (see https://github.com/activeadmin/activeadmin/wiki/How-to-work-with-will_paginate):



```ruby

Kaminari.configure do |config|

  config.page_method_name = :per_page_kaminari

end

```



[activeadmin]: https://github.com/activeadmin/activeadmin

[kaminari]: https://github.com/amatsuda/kaminari

[will_paginate]: https://github.com/mislav/will_paginate



[travis]: https://travis-ci.org/davidcelis/api-pagination

[travis-badge]: http://img.shields.io/travis/davidcelis/api-pagination/master.svg

[coveralls]: https://coveralls.io/r/davidcelis/api-pagination

[coveralls-badge]: http://img.shields.io/coveralls/davidcelis/api-pagination/master.svg

[code-climate]: https://codeclimate.com/github/davidcelis/api-pagination

[code-climate-badge]: http://img.shields.io/codeclimate/github/davidcelis/api-pagination.svg

[gemnasium]: http://gemnasium.com/davidcelis/api-pagination

[gemnasium-badge]: http://img.shields.io/gemnasium/davidcelis/api-pagination.svg

[gittip]: https://gittip.com/davidcelis

[gittip-badge]: http://img.shields.io/gittip/davidcelis.svg