module WillPaginate::Finder::ClassMethods

Paginating finders for ActiveRecord models

WillPaginate adds paginate, per_page and other methods to ActiveRecord::Base class methods and associations. It also hooks into method_missing to intercept pagination calls to dynamic finders such as paginate_by_user_id and translate them to ordinary finders (find_all_by_user_id in this case).

In short, paginating finders are equivalent to ActiveRecord finders; the only difference is that we start with “paginate” instead of “find” and that :page is required parameter:

@posts = Post.paginate :all, :page => params[:page], :order => 'created_at DESC'

In paginating finders, “all” is implicit. There is no sense in paginating a single record, right? So, you can drop the :all argument:

Post.paginate(...)              =>  Post.find :all
Post.paginate_all_by_something  =>  Post.find_all_by_something
Post.paginate_by_something      =>  Post.find_all_by_something

The importance of the `:order` parameter

In ActiveRecord finders, :order parameter specifies columns for the ORDER BY clause in SQL. It is important to have it, since pagination only makes sense with ordered sets. Without the ORDER BY clause, databases aren’t required to do consistent ordering when performing SELECT queries; this is especially true for PostgreSQL.

Therefore, make sure you are doing ordering on a column that makes the most sense in the current context. Make that obvious to the user, also. For perfomance reasons you will also want to add an index to that column.

Public Instance Methods

paginate(*args) { |*a| ... } click to toggle source

This is the main paginating finder.

Special parameters for paginating finders

:page – REQUIRED, but defaults to 1 if false or nil
:per_page – defaults to CurrentModel.per_page (which is 30 if not overridden)
:total_entries – use only if you manually count total entries
:count – additional options that are passed on to count
:finder – name of the ActiveRecord finder used (default: “find”)

All other options (conditions, order, …) are forwarded to find and count calls.

# File lib/will_paginate/finder.rb, line 64
def paginate(*args)
  options = args.pop
  page, per_page, total_entries = wp_parse_options(options)
  finder = (options[:finder] || 'find').to_s

  if finder == 'find'
    # an array of IDs may have been given:
    total_entries ||= (Array === args.first and args.first.size)
    # :all is implicit
    args.unshift(:all) if args.empty?
  end

  WillPaginate::Collection.create(page, per_page, total_entries) do |pager|
    count_options = options.except :page, :per_page, :total_entries, :finder
    find_options = count_options.except(:count).update(:offset => pager.offset, :limit => pager.per_page) 
    
    args << find_options
    # @options_from_last_find = nil
    pager.replace(send(finder, *args) { |*a| yield(*a) if block_given? })
    
    # magic counting for user convenience:
    pager.total_entries = wp_count(count_options, args, finder) unless pager.total_entries
  end
end

paginate_by_sql(sql, options) click to toggle source

Wraps find_by_sql by simply adding LIMIT and OFFSET to your SQL string based on the params otherwise used by paginating finds: page and per_page.

Example:

@developers = Developer.paginate_by_sql ['select * from developers where salary > ?', 80000],
                       :page => params[:page], :per_page => 3

A query for counting rows will automatically be generated if you don’t supply :total_entries. If you experience problems with this generated SQL, you might want to perform the count manually in your application.

# File lib/will_paginate/finder.rb, line 132
def paginate_by_sql(sql, options)
  WillPaginate::Collection.create(*wp_parse_options(options)) do |pager|
    query = sanitize_sql(sql.dup)
    original_query = query.dup
    # add limit, offset
    add_limit! query, :offset => pager.offset, :limit => pager.per_page
    # perfom the find
    pager.replace find_by_sql(query)
    
    unless pager.total_entries
      count_query = original_query.sub /\bORDER\s+BY\s+[\w`,\s]+$/i, ''
      count_query = "SELECT COUNT(*) FROM (#{count_query})"
      
      unless self.connection.adapter_name =~ /^(oracle|oci$)/
        count_query << ' AS count_table'
      end
      # perform the count query
      pager.total_entries = count_by_sql(count_query)
    end
  end
end

paginated_each(options = {}) { |item| ... } click to toggle source

Iterates through all records by loading one page at a time. This is useful for migrations or any other use case where you don’t want to load all the records in memory at once.

It uses paginate internally; therefore it accepts all of its options. You can specify a starting page with :page (default is 1). Default :order is "id", override if necessary.

See Faking Cursors in ActiveRecord where Jamis Buck describes this and a more efficient way for MySQL.

# File lib/will_paginate/finder.rb, line 99
def paginated_each(options = {})
  order = scope(:find, :order) || 'id'
  options = { :order => order, :page => 1 }.merge options
  options[:page] = options[:page].to_i
  options[:total_entries] = 0 # skip the individual count queries
  total = 0
  
  begin 
    collection = paginate(options)
    with_exclusive_scope(:find => {}) do
      # using exclusive scope so that the block is yielded in scope-free context
      total += collection.each { |item| yield item }.size
    end
    options[:page] += 1
  end until collection.size < collection.per_page
  
  total
end

Protected Instance Methods

respond_to_missing?(method, include_private = false) click to toggle source

# File lib/will_paginate/finder.rb, line 165
def respond_to_missing?(method, include_private = false)
  method.to_s.index('paginate') == 0 || super
end

wp_count(options, args, finder) click to toggle source

Does the not-so-trivial job of finding out the total number of entries in the database. It relies on the ActiveRecord count method.

# File lib/will_paginate/finder.rb, line 194
def wp_count(options, args, finder)
  excludees = [:count, :order, :limit, :offset, :readonly]
  excludees << :from unless ActiveRecord::Calculations::CALCULATIONS_OPTIONS.include?(:from)

  # we may be in a model or an association proxy
  klass = (@owner and @reflection) ? @reflection.klass : self

  # Use :select from scope if it isn't already present.
  options[:select] = scope(:find, :select) unless options[:select]

  if options[:select] and options[:select] =~ /^\s*DISTINCT\b/
    # Remove quoting and check for table_name.*-like statement.
    if options[:select].gsub(/[`"]/, '') =~ /\w+\.\*/
      options[:select] = "DISTINCT #{klass.table_name}.#{klass.primary_key}"
    end
  else
    excludees << :select # only exclude the select param if it doesn't begin with DISTINCT
  end

  # count expects (almost) the same options as find
  count_options = options.except *excludees

  # merge the hash found in :count
  # this allows you to specify :select, :order, or anything else just for the count query
  count_options.update options[:count] if options[:count]

  # forget about includes if they are irrelevant (Rails 2.1)
  if count_options[:include] and
      klass.private_methods.include_method?(:references_eager_loaded_tables?) and
      !klass.send(:references_eager_loaded_tables?, count_options)
    count_options.delete :include
  end

  # we may have to scope ...
  counter = Proc.new { count(count_options) }

  count = if finder.index('find_') == 0 and klass.respond_to?(scoper = finder.sub('find', 'with'))
            # scope_out adds a 'with_finder' method which acts like with_scope, if it's present
            # then execute the count with the scoping provided by the with_finder
            send(scoper, &counter)
          elsif finder =~ /^find_(all_by|by)_([_a-zA-Z]\w*)$/
            # extract conditions from calls like "paginate_by_foo_and_bar"
            attribute_names = $2.split('_and_')
            conditions = construct_attributes_from_arguments(attribute_names, args)
            with_scope(:find => { :conditions => conditions }, &counter)
          else
            counter.call
          end

  (!count.is_a?(Integer) && count.respond_to?(:length)) ? count.length : count
end