Class WillPaginate::Collection
In: lib/will_paginate/collection.rb
Parent: Array

The key to pagination

Arrays returned from paginating finds are, in fact, instances of this little class. You may think of WillPaginate::Collection as an ordinary array with some extra properties. Those properties are used by view helpers to generate correct page links.

WillPaginate::Collection also assists in rolling out your own pagination solutions: see create.

If you are writing a library that provides a collection which you would like to conform to this API, you don‘t have to copy these methods over; simply make your plugin/gem dependant on this library and do:

  require 'will_paginate/collection'
  # WillPaginate::Collection is now available for use

Methods

create   new   offset   replace   total_entries=  

Included Modules

CollectionMethods

Attributes

current_page  [R] 
per_page  [R] 
total_entries  [R] 

Public Class methods

Just like new, but yields the object after instantiation and returns it afterwards. This is very useful for manual pagination:

  @entries = WillPaginate::Collection.create(1, 10) do |pager|
    result = Post.find(:all, :limit => pager.per_page, :offset => pager.offset)
    # inject the result array into the paginated collection:
    pager.replace(result)

    unless pager.total_entries
      # the pager didn't manage to guess the total count, do it manually
      pager.total_entries = Post.count
    end
  end

The possibilities with this are endless. For another example, here is how WillPaginate used to define pagination for Array instances:

  Array.class_eval do
    def paginate(page = 1, per_page = 15)
      WillPaginate::Collection.create(page, per_page, size) do |pager|
        pager.replace self[pager.offset, pager.per_page].to_a
      end
    end
  end

The Array#paginate API has since then changed, but this still serves as a fine example of WillPaginate::Collection usage.

Arguments to the constructor are the current page number, per-page limit and the total number of entries. The last argument is optional because it is best to do lazy counting; in other words, count conditionally after populating the collection using the replace method.

Public Instance methods

Current offset of the paginated collection. If we‘re on the first page, it is always 0. If we‘re on the 2nd page and there are 30 entries per page, the offset is 30. This property is useful if you want to render ordinals side by side with records in the view: simply start with offset + 1.

This is a magic wrapper for the original Array#replace method. It serves for populating the paginated collection after initialization.

Why magic? Because it tries to guess the total number of entries judging by the size of given array. If it is shorter than per_page limit, then we know we‘re on the last page. This trick is very useful for avoiding unnecessary hits to the database to do the counting after we fetched the data for the current page.

However, after using replace you should always test the value of total_entries and set it to a proper value if it‘s nil. See the example in create.

[Validate]