Class: Leaf::Collection

Inherits:
Array
  • Object
show all
Defined in:
lib/leaf/collection.rb

Overview

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

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Array

#include_method?, #paginate

Constructor Details

#initialize(page, per_page, total = nil) ⇒ Collection

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.

Raises:



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# 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

Instance Attribute Details

#current_page ⇒ Object (readonly)

Returns the value of attribute current_page.



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# File 'lib/leaf/collection.rb', line 23

def current_page
  @current_page
end

#per_page ⇒ Object (readonly)

Returns the value of attribute per_page.



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# File 'lib/leaf/collection.rb', line 23

def per_page
  @per_page
end

#total_entries ⇒ Object

Returns the value of attribute total_entries.



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# File 'lib/leaf/collection.rb', line 23

def total_entries
  @total_entries
end

#total_pages ⇒ Object (readonly)

Returns the value of attribute total_pages.



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# File 'lib/leaf/collection.rb', line 23

def total_pages
  @total_pages
end

Class Method Details

.create(page, per_page, total = nil) {|pager| ... } ⇒ Object

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

Yields:

  • (pager) 


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# 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

Instance Method Details

#next_page ⇒ Object

current_page + 1 or nil if there is no next page



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# File 'lib/leaf/collection.rb', line 67

def next_page
  current_page < total_pages ? (current_page + 1) : nil
end

#offset ⇒ Object

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.



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# File 'lib/leaf/collection.rb', line 57

def offset
  (current_page - 1) * per_page
end

#out_of_bounds? ⇒ Boolean

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.

Returns:

  • (Boolean) 


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# File 'lib/leaf/collection.rb', line 49

def out_of_bounds?
  current_page > total_pages
end

#previous_page ⇒ Object

current_page - 1 or nil if there is no previous page



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# File 'lib/leaf/collection.rb', line 62

def previous_page
  current_page > 1 ? (current_page - 1) : nil
end

#replace(array) ⇒ Object

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.



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# 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