Paginate in your headers, not in your response body. This follows the proposed RFC-5988 standard for Web linking.
# 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 'kaminari' gem 'will_paginate' # Finally... gem 'api-pagination'
By default, api-pagination will detect whether you're using Kaminari or WillPaginate, and name headers appropriately. If you want to change any of the configurable settings, you may do so:
ApiPagination.configure do |config| # If you have both gems 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: what parameter should be used to set the page option config.page_param = :page # or config.page_param do |params| params[:page][:number] 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] end end
In your controller, provide a pageable collection to the
paginate method. In its most convenient form,
paginate simply mimics
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
xml option, paginate it for you using
params[:per_page], render Link headers, and call
ActionController::Base#render with whatever you passed to
paginate. This should work well with ActiveModel::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:
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.
paginate is used to declare that your endpoint takes a
: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:
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 end end
curl --include to see your header-based pagination in action:
$ curl --include 'https://localhost:3000/movies?page=5' HTTP/1.1 200 OK Link: <http://localhost:3000/movies?page=1>; rel="first", <http://localhost:3000/movies?page=173>; rel="last", <http://localhost:3000/movies?page=6>; rel="next", <http://localhost:3000/movies?page=4>; 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 (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:
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):
Kaminari.configure do |config| config.page_method_name = :per_page_kaminari end