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module ActionController
# === Action Pack pagination for Active Record collections
# The Pagination module aids in the process of paging large collections of
# Active Record objects. It offers macro-style automatic fetching of your
# model for multiple views, or explicit fetching for single actions. And if
# the magic isn't flexible enough for your needs, you can create your own
# paginators with a minimal amount of code.
# The Pagination module can handle as much or as little as you wish. In the
# controller, have it automatically query your model for pagination; or,
# if you prefer, create Paginator objects yourself.
# For help rendering pagination links, see
# ActionView::Helpers::PaginationHelper.
# ==== Automatic pagination for every action in a controller
# class PersonController < ApplicationController
# helper :pagination
# model :person
# paginate :people, :order_by => 'last_name, first_name',
# :per_page => 20
# # ...
# end
# Each action in this controller now has access to a <tt>@people</tt>
# instance variable, which is an ordered collection of model objects for the
# current page (at most 20, sorted by last name and first name), and a
# <tt>@person_pages</tt> Paginator instance. The current page is determined
# by the <tt>@params['page']</tt> variable.
# ==== Pagination for a single action
# def list
# @person_pages, @people =
# paginate :people, :order_by => 'last_name, first_name'
# end
# Like the previous example, but explicitly creates <tt>@person_pages</tt>
# and <tt>@people</tt> for a single action, and uses the default of 10 items
# per page.
# ==== Custom/"classic" pagination
# def list
# @person_pages = self, Person.count, 10, @params['page']
# @people = Person.find_all nil, 'last_name, first_name',
# @person_pages.current.to_sql
# end
# Explicitly creates the paginator from the previous example and uses
# Paginator#to_sql to retrieve <tt>@people</tt> from the model.
module Pagination
unless const_defined?(:OPTIONS)
# A hash holding options for controllers using macro-style pagination
# The default options for pagination
:class_name => nil,
:per_page => 10,
:conditions => nil,
:order_by => nil,
:join => nil,
:parameter => 'page'
def self.included(base) #:nodoc:
def self.validate_options!(collection_id, options, in_action) #:nodoc:
options.merge!(DEFAULT_OPTIONS) {|key, old, new| old}
valid_options = DEFAULT_OPTIONS.keys
valid_options << :actions unless in_action
unknown_option_keys = options.keys - valid_options
raise ActionController::ActionControllerError,
"Unknown options: #{unknown_option_keys.join(', ')}" unless
options[:singular_name] = Inflector.singularize(collection_id.to_s)
options[:class_name] ||= Inflector.camelize(options[:singular_name])
# Returns a paginator and a collection of Active Record model instances
# for the paginator's current page. This is designed to be used in a
# single action; to automatically paginate multiple actions, consider
# ClassMethods#paginate.
# +options+ are:
# <tt>:class_name</tt>:: the class name to use, if it can't be inferred by
# singularizing the collection name
# <tt>:per_page</tt>:: the maximum number of items to include in a
# single page. Defaults to 10
# <tt>:conditions</tt>:: optional conditions passed to Model.find_all and
# Model.count
# <tt>:order_by</tt>:: optional order parameter passed to Model.find_all
# <tt>:join</tt>:: optional join parameter passed to Model.find_all
# and Model.count
def paginate(collection_id, options={})
Pagination.validate_options!(collection_id, options, true)
paginator_and_collection_for(collection_id, options)
# These methods become class methods on any controller which includes
# PaginationHelper.
module ClassMethods
# Creates a +before_filter+ which automatically paginates an Active
# Record model for all actions in a controller (or certain actions if
# specified with the <tt>:actions</tt> option).
# +options+ are the same as PaginationHelper#paginate, with the addition
# of:
# <tt>:actions</tt>:: an array of actions for which the pagination is
# active. Defaults to +nil+ (i.e., every action)
def paginate(collection_id, options={})
Pagination.validate_options!(collection_id, options, false)
module_eval do
before_filter :create_paginators_and_retrieve_collections
OPTIONS[self] ||=
OPTIONS[self][collection_id] = options
def create_paginators_and_retrieve_collections #:nodoc:
Pagination::OPTIONS[self.class].each do |collection_id, options|
next unless options[:actions].include? action_name if
paginator, collection =
paginator_and_collection_for(collection_id, options)
paginator_name = "@#{options[:singular_name]}_pages"
self.instance_variable_set(paginator_name, paginator)
collection_name = "@#{collection_id.to_s}"
self.instance_variable_set(collection_name, collection)
# Returns the total number of items in the collection to be paginated for
# the +model+ and given +conditions+. Override this method to implement a
# custom counter.
def count_collection_for_pagination(model, conditions)
# Returns a collection of items for the given +model+ and +conditions+,
# ordered by +order_by+, for the current page in the given +paginator+.
# Override this method to implement a custom finder.
def find_collection_for_pagination(model, conditions, order_by, join, paginator)
model.find_all(conditions, order_by, paginator.current.to_sql, join)
protected :create_paginators_and_retrieve_collections,
def paginator_and_collection_for(collection_id, options) #:nodoc:
klass = eval options[:class_name]
page = @params[options[:parameter]]
count = count_collection_for_pagination(klass, options[:conditions])
paginator =, count, options[:per_page], page)
collection = find_collection_for_pagination(klass,
options[:conditions], options[:order_by], options[:join], paginator)
return paginator, collection
private :paginator_and_collection_for
# A class representing a paginator for an Active Record collection.
class Paginator
include Enumerable
# Creates a new Paginator on the given +controller+ for a set of items
# of size +item_count+ and having +items_per_page+ items per page.
# Raises ArgumentError if items_per_page is out of bounds (i.e., less
# than or equal to zero). The page CGI parameter for links defaults to
# "page" and can be overridden with +page_parameter+.
def initialize(controller, item_count, items_per_page, current_page=1)
raise ArgumentError, 'must have at least one item per page' if
items_per_page <= 0
@controller = controller
@item_count = item_count || 0
@items_per_page = items_per_page
self.current_page = current_page
attr_reader :controller, :item_count, :items_per_page
# Sets the current page number of this paginator. If +page+ is a Page
# object, its +number+ attribute is used as the value; if the page does
# not belong to this Paginator, an ArgumentError is raised.
def current_page=(page)
if page.is_a? Page
raise ArgumentError, 'Page/Paginator mismatch' unless
page.paginator == self
page = page.to_i
@current_page = has_page_number?(page) ? page : 1
# Returns a Page object representing this paginator's current page.
def current_page
alias current :current_page
# Returns a new Page representing the first page in this paginator.
def first_page
alias first :first_page
# Returns a new Page representing the last page in this paginator.
def last_page
alias last :last_page
# Returns the number of pages in this paginator.
def page_count
return 1 if
(@item_count / @items_per_page.to_f).ceil
alias length :page_count
# Returns true if this paginator contains the page of index +number+.
def has_page_number?(number)
return false unless number.is_a? Fixnum
number >= 1 and number <= page_count
# Returns a new Page representing the page with the given index
# +number+.
def [](number), number)
# Successively yields all the paginator's pages to the given block.
def each(&block)
page_count.times do |n|
yield self[n+1]
# A class representing a single page in a paginator.
class Page
include Comparable
# Creates a new Page for the given +paginator+ with the index
# +number+. If +number+ is not in the range of valid page numbers or
# is not a number at all, it defaults to 1.
def initialize(paginator, number)
@paginator = paginator
@number = number.to_i
@number = 1 unless @paginator.has_page_number? @number
attr_reader :paginator, :number
alias to_i :number
# Compares two Page objects and returns true when they represent the
# same page (i.e., their paginators are the same and they have the
# same page number).
def ==(page)
return false if page.nil?
@paginator == page.paginator and
@number == page.number
# Compares two Page objects and returns -1 if the left-hand page comes
# before the right-hand page, 0 if the pages are equal, and 1 if the
# left-hand page comes after the right-hand page. Raises ArgumentError
# if the pages do not belong to the same Paginator object.
def <=>(page)
raise ArgumentError unless @paginator == page.paginator
@number <=> page.number
# Returns the item offset for the first item in this page.
def offset
@paginator.items_per_page * (@number - 1)
# Returns the number of the first item displayed.
def first_item
offset + 1
# Returns the number of the last item displayed.
def last_item
[@paginator.items_per_page * @number, @paginator.item_count].min
# Returns true if this page is the first page in the paginator.
def first?
self == @paginator.first
# Returns true if this page is the last page in the paginator.
def last?
self == @paginator.last
# Returns a new Page object representing the page just before this
# page, or nil if this is the first page.
def previous
if first? then nil else, @number - 1) end
# Returns a new Page object representing the page just after this
# page, or nil if this is the last page.
def next
if last? then nil else, @number + 1) end
# Returns a new Window object for this page with the specified
# +padding+.
def window(padding=2), padding)
# Returns the limit/offset array for this page.
def to_sql
[@paginator.items_per_page, offset]
def to_param #:nodoc:
# A class for representing ranges around a given page.
class Window
# Creates a new Window object for the given +page+ with the specified
# +padding+.
def initialize(page, padding=2)
@paginator = page.paginator
@page = page
self.padding = padding
attr_reader :paginator, :page
# Sets the window's padding (the number of pages on either side of the
# window page).
def padding=(padding)
@padding = padding < 0 ? 0 : padding
# Find the beginning and end pages of the window
@first = @paginator.has_page_number?(@page.number - @padding) ?
@paginator[@page.number - @padding] : @paginator.first
@last = @paginator.has_page_number?(@page.number + @padding) ?
@paginator[@page.number + @padding] : @paginator.last
attr_reader :padding, :first, :last
# Returns an array of Page objects in the current window.
def pages
(@first.number..@last.number) {|n| @paginator[n]}
alias to_a :pages
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