class Leaf::Collection

The key to pagination

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

gem 'leaf'
require 'leaf/collection'

# now use Leaf::Collection directly or subclass it

Attributes

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

Public Class Methods

create(page, per_page, total = nil) { |pager| ... } click to toggle source

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

# File lib/leaf/collection.rb, line 40
def self.create(page, per_page, total = nil, &block)
  pager = new(page, per_page, total)
  yield pager
  pager
end
new(page, per_page, total = nil) click to toggle source

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/leaf/collection.rb, line 29
def initialize(page, per_page, total = nil)
  @current_page = page.to_i
  raise InvalidPage.new(page, @current_page) if @current_page < 1
  @per_page = per_page.to_i
  raise ArgumentError, "`per_page` setting cannot be less than 1 (#{@per_page} given)" if @per_page < 1
  
  self.total_entries = total if total
end

Public Instance Methods

next_page() click to toggle source

current_page + 1 or nil if there is no next page

# File lib/leaf/collection.rb, line 67
def next_page
  current_page < total_pages ? (current_page + 1) : nil
end
offset() click to toggle source

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 besides your records: simply start with offset + 1.

# File lib/leaf/collection.rb, line 57
def offset
  (current_page - 1) * per_page
end
out_of_bounds?() click to toggle source

Helper method that is true when someone tries to fetch a page with a larger number than the last page. Can be used in combination with flashes and redirecting.

# File lib/leaf/collection.rb, line 49
def out_of_bounds?
  current_page > total_pages
end
previous_page() click to toggle source

current_page - 1 or nil if there is no previous page

# File lib/leaf/collection.rb, line 62
def previous_page
  current_page > 1 ? (current_page - 1) : nil
end
replace(array) click to toggle source

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.

Calls superclass method
# File lib/leaf/collection.rb, line 88
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
total_entries=(number) click to toggle source
# File lib/leaf/collection.rb, line 71
def total_entries=(number)
  @total_entries = number.to_i
  @total_pages   = (@total_entries / per_page.to_f).ceil
end