Folio

Folio is a library for pagination. It's meant to be nearly compatible with WillPaginate, but with broader -- yet more well-defined -- semantics to allow for sources whose page identifiers are non-ordinal (i.e. a page identifier of 3 does not necessarily indicate the third page).

Add this line to your application's Gemfile:

gem 'folio-pagination'

And then execute:

$ bundle

Or install it yourself as:

$ gem install folio-pagination

To use Folio's optional Rails support, you will need to load the 'will_paginate' gem into your application along with folio, but don't require it. For instance in your Gemfile:

gem 'will_paginate', require: false

And then you can:

require 'folio/rails'

This will load just the necessary portions of the will_paginate gem.

The core Folio interface is defined by two mixins. Mixing Folio into a source of items creates a "folio" and provides pagination on that folio. Mixing Folio::Page into a subset of items from a folio creates a "page" with additional properties relating it to the folio and the other pages in the folio.

Folio also provides some basic implementations, both standalone and by mixing these modules in to familiar classes.

You can mix Folio::Page into any Enumerable. The mixin gives you eight attributes and one method:

• ordinal_pages? indicates whether the page identifiers in current_page, first_page, last_page, previous_page, and next_page should be considered ordinal or not.

• current_page is the page identifier addressing this page within the folio.

• per_page is the number of items requested from the folio when filling this page.

• first_page is the page identifier addressing the first page within the folio.

• last_page is the page identifier addressing the final page within the folio, if known.

• next_page is the page identifier addressing the immediately following page within the folio, if there is one.

• previous_page is the page identifier addressing the immediately preceding page within the folio, if there is one and it is known.

• total_entries is the number of items in the folio, if known.

• total_pages if the number of pages in the folio, if known. It is calculated from total_entries and per_page.

ordinal_pages?, first_page, and last_page are common to all pages created by a folio and are configured, as available, when the folio creates a blank page in its build_page method (see below).

current_page, per_page, and total_entries control the filling of a page and are configured from parameters to the folio's paginate method.

next_page and previous_page are configured, as available, when the folio fills the configured page in its fill_page method (see below).

You can mix Folio into any class implementing two methods:

• build_page is responsible for instantiating a Folio::Page and configuring its ordinal_pages?, first_page, and last_page attributes.

• fill_page will receive a Folio::Page with the ordinal_pages?, first_page, last_page, current_page, per_page, and total_entries attributes configured, and should populate the page with the corresponding items from the folio. It should also set appropriate values for the next_page and previous_page attributes on the page. If the value provided in the page's current_page cannot be interpreted as addressing a page in the folio, Folio::InvalidPage should be raised.

In return, Folio provides a paginate method and per_page attributes for both the folio class and for individual folio instances.

The paginate method coordinates the page creation, configuration, and population. It takes three parameters: page, per_page, and total_entries, each optional.

• page configures the page's current_page, defaulting to the page's first_page.

• per_page configures the page's per_page, defaulting to the folio's per_page attribute.

• total_entries configures the page's total_entries, if present. otherwise, if the folio implements a count method, the page's total_entries will be set from that method.

NOTE: providing a total_entries parameter of nil will still bypass the count method, leaving total_entries nil. This is useful when the count would be too expensive and you'd rather just leave the number of entries unknown.

The per_page attribute added to the folio instance will default to the per_page attribute from the folio class when unset. The per_page class attribute added to the folio class will default to global Folio.per_page when unset.

A typical use case for pagination deals with ordinal page identifiers; e.g. "1" means the first page, "2" means the second page, etc.

As a matter of convenience for these use cases, additional mixins of Folio::Ordinal and Folio::Ordinal::Page are provided.

Mixing Folio::Ordinal::Page into an Enumerable provides the same methods as Folio::Page but with the following overrides:

• ordinal_pages is always true

• first_page is always 1

• previous_page is always either current_page-1 or nil, depending on how current_page relates to first_page.

• next_page can only be set if total_pages is unknown. if total_pages is known, next_page will be either current_page+1 or nil, depending on how current_page relates to last_page. if total_pages is unknown and next_page is unset (vs. explicitly set to nil), it will default to current_page+1.

• last_page is deterministic: always total_pages if total_pages is known, current_page if total_pages is unknown and next_page is nil, nil otherwise (indicating the page sequence continues until next_page is nil).

Similarly, mixing Folio::Ordinal into a source provides the same methods as Folio, but simplifies your build_page and fill_page methods by moving some responsibility into the paginate method. build_page also has a default implementation.

• build_page no longer needs to configure ordinal_page?, first_page, or last_page on the instantiated page. Instead, just instantiate and return a Folio::Page or Folio::Ordinal::Page. Then ordinal_page?, first_page, and last_page are handled for you, as described above. If not provided, the default implementation just returns a subclass of Array setup to be a Folio::Ordinal::Page.

• fill_page no longer needs to configure next_page and previous_page; the ordinal page will handle them. (Note that if necessary, you can still set next_page explicitly to nil.) Also, paginate will now perform ordinal bounds checking for you, so you can focus entirely on populating the page.

Often times you just want to take the simplest collection possible. One way would be to subclass Array and mixin Folio::Page, then instantiate the subclass. When you want to add more, or Array isn't the proper superclass, you can still do this.

For the common case we've already done it. This is the Folio::BasicPage class. We've also provided a shortcut for instantiating one: Folio::Page.create. So, for example, a simple build_page method could just be:

  def build_page
    page = Folio::Page.create
    # setup ordinal_pages?, first_page, etc.
    page
  end

Folio::Ordinal::BasicPage and Folio::Ordinal::Page.create are also available, respectively, for the ordinal case.

If you require folio/core_ext/enumerable, all Enumerables will be extended with Folio::Ordinal and naive build_page and fill_page methods.

build_page will simply return a basic ordinal page as from Folio::Page::Ordinal.create. fill_page then selects an appropriate range of items from the folio using standard Enumerable methods, then calls replace on the page (it's a Folio::Ordinal::BasicPage) with this subset.

This lets you do things like:

require 'folio/core_ext/enumerable'

natural_numbers = Enumerator.new do |enum|
  n = 0
  loop{ enum.yield(n += 1) }
end
page = natural_numbers.paginate(page: 3, per_page: 5, total_entries: nil)

page.ordinal_pages?  #=> true
page.per_page        #=> 5
page.first_page      #=> 1
page.previous_page   #=> 2
page.current_page    #=> 3
page.next_page       #=> 4
page.last_page       #=> nil
page.total_entries   #=> nil
page.total_pages     #=> nil
page                 #=> [11, 12, 13, 14, 15]

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. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request