Perform a Rails find() and iterate over the resulting records in groups

mcmire () — Mon, 05 May 2008 15:35:43 GMT



module ActiveRecord

  class Base

    # This method lets you iterate over the results of a .find, in groups.

    # (Basically an interface to LIMIT.)

    # Anything you can pass as options to .find, you can pass here. 

    # Example 1:

    #   Order.each_by(100, :conditions => { :cc_processed_at => nil }) do |order|

    #     # do stuff with order

    #   end

    # Example 2:

    #   Person.each_by(50, :order => 'name') do |person, index|

    #     # do stuff with person and index

    #   end

    # Pass :update => true in the options to print a message before each group is

    # fetched from the db.

    #

    # Author: Elliot Winkler 

    # Source: http://snippets.dzone.com/posts/show/5461

    def self.each_by(group_size, options={}, &blk)

      update = options.delete(:update) || false

      num_records = count(options.except(:from))

      return 0 if num_records == 0

      #raise "Number of records: #{num_records}"

      also_pass_offset = (blk.arity == 2)

      0.step(num_records, group_size) do |offset|

        find_options = { :offset => offset, :limit => group_size }.merge(options)

        if update

          if num_records == 1

            puts ">> Reading the only record."

          else

            start_offset = offset + 1

            end_offset   = offset + group_size

            end_offset   = num_records if num_records < end_offset

            puts ">> Reading records #{start_offset}-#{end_offset}."

          end

        end 

        find(:all, find_options).each do |record|

          also_pass_offset ? blk.call(record, offset) : blk.call(record)

        end

      end

      num_records

    end

  end

end

Also see:

* http://weblog.jamisbuck.org/2007/4/6/faking-cursors-in-activerecord
* http://weblog.jamisbuck.org/2007/2/28/poor-man-s-pagination

DZone Snippets: find code

Perform a Rails find() and iterate over the resulting records in groups