class WillPaginate::Collection
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
Attributes
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.
# File lib/will_paginate/collection.rb, line 94 def self.create(page, per_page, total = nil) pager = new(page, per_page, total) yield pager pager end
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.
# File lib/will_paginate/collection.rb, line 61 def initialize(page, per_page = WillPaginate.per_page, total = nil) @current_page = WillPaginate::PageNumber(page) @per_page = per_page.to_i self.total_entries = total if total end
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.
# File lib/will_paginate/collection.rb, line 104 def offset current_page.to_offset(per_page).to_i end
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
.
# File lib/will_paginate/collection.rb, line 124 def replace(array) result = super # The collection is shorter then page limit? Rejoice, because # then we know that we are on the last page! if total_entries.nil? and length < per_page and (current_page == 1 or length > 0) self.total_entries = offset + length end result end
# File lib/will_paginate/collection.rb, line 108 def total_entries=(number) @total_entries = number.to_i end