Wor::Paginate

Table of contents

• Description
• Installation
• Usage
  • Basic usage
  • Customizing output
    • Custom serializers
    • Custom options
    • Custom formatters
    • Custom adapters
  • Working with Kaminari or will_paginate
  • Test helpers
• Contributing
• Releases
• About
• License

---

Description

Wor::Paginate is a gem for Rails that simplifies pagination, particularly for controller methods, while standardizing JSON output for APIs. It's meant to work both as a standalone pagination gem and as an extra layer over Kaminari and will_paginate.

Installation

Add the following line to your application's Gemfile:

gem 'wor-paginate'

And then execute:

$ bundle

Or install it yourself as:

$ gem install wor-paginate

Then you can run rails generate wor:paginate:install to create the initializer for configuration details, including default formatter class, page and limit params and default page number.

Usage

Basic usage

The basic use case is to paginate using default values. This is achieved by including the module in a controller and calling render_paginate in the method that needs pagination.

  class DummyModelsController < ApplicationController
    include Wor::Paginate

    def index
      render_paginated DummyModel
    end
  end

The first parameter to render_paginated can be multiple things:

• ActiveRecord/ActiveRecord::Relation
• Enumerables (for example, arrays and ranges)
• Pre-paginated Kaminari or will_paginate relations (original pagination will be ignored)

The response to the index will then be:

{
  "page": [
    {
      "id": 1,
      "name": "1c",
      "something": 27
    },
    {
      "id": 2,
      "name": "i",
      "something": 68
    },
    // ...
    {
      "id": 25,
      "name": "2m",
      "something": 32
    }
  ],
  "count": 25,
  "total_pages": 2,
  "total_count": 28,
  "current_page": 1,
  "previous_page": null,
  "next_page": 2,
  "previous_page_url": null,
  "next_page_url": "http://api.example.com/users?page=2
}

Page number is passed through the page option of the render_paginated method. If none is supplied, params[:page] will be used, (or the default parameter configured in the initializer). By default, if the page parameter is not present we will use 1 as the page (or the default page parameter configured in the initializer). The amount of items is passed through the limit option of the render_paginated method. If none is supplied, params[:limit] will be used (or the default parameter configured in the initializer). Default is 25. The default serializer and formatter will be used.

Customizing output

Custom serializers

A custom serializer for each object can be passed using the each_serializer option:

render_paginated DummyModel, each_serializer: CustomDummyModelSerializer

where the serializer is just an ActiveModel::Serializer.

Custom options

max_limit

The max amount of items is passed through the max_limit option, You can set the value in the initializer or in the render_paginated method, (If none is supplied, take the default value configured in the initializer). Default is 50.

  render_paginated DummyModel, max_limit: 100

current_user

Using custom options in serializer, example method current_user

render_paginated DummyModel, each_serializer: CustomDummyModelSerializer, current_user: current_user

In serializer

class CustomSerializer < ActiveModel::Serializer
  def method
    @instance_options[:current_user]
  end
end

total_count

You can overwrite the total_count pagination param by passing it as a single option to the method. This could be used if the whole collection to be paginated is complex and has the risk to broke when counting all the records.

  render_paginated DummyModel, total_count: 50

preserve_records

WARNING: This option only works with an ActiveRecord collection.

Preserve records option can be added to render_paginated to mantain current records. This allow to navigate pages like an infinite scroll without adding new records when switching pages.

• Timestamp mode (default)

def index
  render_paginated SomeModel, preserve_records: true 
end

# You can customize the field used to preserve this records (default is 'created_at')
def index
  render_paginated SomeModel, preserve_records: { by: :timestamp, field: :custom_time_field } 
end

• PK mode

def index
  render_paginated SomeModel, preserve_records: { by: :id } 
end

# You can customize the field used to preserve this records (default is 'id')
def index
  render_paginated SomeModel, preserve_records: { by: :id, field: :my_custom_id_field }
end

Custom formatters

A formatter is an object that defines the output of the render_paginated method. In case the application needs a different format for a request, it can be passed to the render_paginated method using the formatter option:

render_paginated DummyModel, formatter: CustomFormatter

or it can also be set as a default in the initializer.

A new formatter can be created inheriting from the default one. The format method should be redefined returning something that can be converted to json.

class CustomFormatter < Wor::Paginate::Formatters::Base
  def format
    { page: serialized_content, current: current_page }
  end
end

Available helper methods are:

• current_page: integer with the current page
• count: number of items in the page (post-pagination)
• total_count: number of total items (pre-pagination)
• total_pages: number of pages given the current limit (post-pagination)
• paginated_content: its class depends on the original content passed to render_paginated, it's the paginated but not yet serialized content.
• serialized_content: array with all the items after going through the serializer (either the default or a supplied one)

Custom adapters

An adapter is an object that defines how to show the rendered content, and how to calculate several methods of the pagination, such as 'total_count', 'total_pages', 'paginated_content' among others. In case the application needs a different adapter or a custom one, it can be passed to the render_paginated method using the adapter option:

render_paginated DummyModel, adapter: CustomAdapter

or it can also be set as a default in the initializer.

A new adapter can be created inheriting from the default Base Adapter. Some methods must be redefined in order to make the adapter "adaptable" to the content that will be rendered. Below is an example of a simple posible CustomAdapter that extends from the base Adapter.

class CustomAdapter < Wor::Paginate::Adapters::Base
  def required_methods
    %i[count]
  end

  def paginated_content
    @paginated_content ||= @content.first(5)
  end

  def total_pages
    (total_count / @limit.to_f).ceil
  end

  def total_count
    @content.count
  end

  delegate :count, to: :paginated_content
end

Here's a brief explanation on every overwritten method in this CustomAdapter example:

#required_methods

These will be the methods (as symbols) that the content to be rendered has to support. The next expression will be evaluated for every method added here: @content.respond_to? method. All required_methods must answer true to the previous expression, in order to make the adapter "adaptable" for the content. For example, if we rendered an ActiveRecord::Relation, this CustomAdapter would be adaptable because an ActiveRecord::Relation responds to the #count method. At least one symbol has to be returned in this method, otherwise the adapter won't be able to render content.

#paginated_content

This is how the content will be shown. As the content comes in the inherited instance variable @content, we can transform the content however we want. In the CustomAdapter example, will always be shown the first 5 records.

#total_pages

This could be defined as the number of pages, given the limit requested. As the other values, this can be a custom number of pages, depending on your needs. For this example, this number is just an integer calculation of the total pages, depending on the limit. Also, like @content, we are inheriting the @limit variable, which allows us to operate with it however we want.

#total_count

This will be the number that will tell us 'how many records is returning the request'. Again, we can customize it however we want. For this particular example this will be just the count of @content.

#count method as delegate

In the end of the CustomAdapter we are delegating the #count method to the paginated_content. This is because the Base Adapter delegates that method to the inherited adapter, so our custom adapter has to know "how to calculate" that method, that's why we are defining a #count method in the delegation (It is always mandatory to define the #count method in a custom adapter, whether is a method definition or a delegate).

If the content is an ActiveRecord::Relation, for example, this adapter would work, because paginated_content would become an ActiveRecord::Relation, which actually knows "how to calculate" the count method. This works as a delegate, because ActiveRecord::Relation has an internal #count definition, but we would have to provide the needed method definition if it is a custom method, or we want a custom behaviour of a known method.

Other available methods to overwrite

Wor::Paginate::Adapters::Base also has implementations for #next_page and #previous_page methods (which calculate the number of the next and previous pages, respectively). If you want, you can also overwrite those methods, to calculate custom 'next' and 'previous' page numbers.

To understand better the implementation of the Base Adapter and how you could overwrite methods in order to make a functional Custom Adapter, take a look at its definition in: Base adapter Class. Keep in mind that an instance of your Custom Adapter must answer true to the #adapt? method inherited from the Base Adapter, in order to make it "adaptable" to the content.

Adapters Operations

There are also helper methods available to dynamically operate the gem's adapters, so you can configurate them, whether in the initializer or in an internal part of your application. Once you include the gem, you'll be provided with the following methods, inside the Config module:

• Wor::Paginate::Config.add_adapter(adapter): Add a specific adapter to the array of the gem's adapters. The 'adapter' variable must be a Class reference to an Adapter Class (that class has to have a similar structure as the CustomAdapter example above).
• Wor::Paginate::Config.remove_adapter(adapter): Remove an specific adapter from the array of the gem's adapters.
• Wor::Paginate::Config.clear_adapters: This method empties the array of the gem's adapters.
• Wor::Paginate::Config.adapters: Returns all the current internal adapters inside the gem.
• Wor::Paginate::Config.reset_adapters!: This helper resets the gem's adapters to its default array of adapters. You can see how the array of default adapters looks like at the beggining of the Wor::Paginate::Config module: Config module.

When the gem paginates, it tries to adapt the content to the first adapter that is "adaptable" for the content (unless a custom adapter has been passed to render_paginated or a default_adapter has been defined in the initializer). So beware of which adapters (and in which order) are you leaving in the Wor::Paginate::Config.adapters array, because depending on those, the gem will try to adapt the content.

Working with Kaminari or will_paginate

If either Kaminari or will_paginate are required in the project, Wor::Paginate will use them for pagination with no code or configuration change.

Test helpers

You can use the be_paginated matcher to test your endpoints. It also accepts the with chain method to receive a formatter.

You only need to add this in your rails_helper.rb

# spec/rails_helper.rb
require 'wor/paginate/rspec'

And in your spec do

# spec/controllers/your_controller.rb
describe YourController do
  let(:response_body) do
    ActiveSupport::JSON.decode(response.body) if response.present? && response.body.present?
  end

  describe '#index' do
    subject(:http_request) { get :index }

    it { expect(response_body).to be_paginated }
  end

  describe '#index_with_custom_formatter' do
    subject(:http_request) { get :index_custom_formatter }

    it 'checks that the response keys matches with the custom formatter' do
      expect(response_body).to be_paginated.with(CustomFormatter)
    end
  end
end

Working with panko-serializer

The default formatter is Active Model Serializer. If you want to change it, you should replace the formatter to another one. In this section, we are going to work with PankoFormatter

example

Wor::Paginate.configure do |config
  config.formatter = Wor::Paginate::Formatters::PankoFormatter
end

and next pass the specific serializer that you can use in the specific endpoint

  def index
    render_paginated DummyModel, each_serializer: DummyModelPankoSerializer
  end

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Run rubocop lint (bundle exec rubocop -R --format simple)
5. Run rspec tests (bundle exec rspec)
6. Push your branch (git push origin my-new-feature)
7. Create a new Pull Request to master branch

Releases

📢 See what's changed in a recent version

About

The current maintainers of this gem are :

• Martín Mallea

This project was developed by:

• Hugo Farji
• Ignacio Coluccio
• Alan Halatian

At Wolox

License

wor-paginate is available under the MIT license.

Copyright (c) 2017 Wolox

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.