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module ActiveRecord
module Batches # :nodoc:
extend ActiveSupport::DependencyModule
# When processing large numbers of records, it's often a good idea to do
# so in batches to prevent memory ballooning.
module ClassMethods
# Yields each record that was found by the find +options+. The find is
# performed by find_in_batches with a batch size of 1000 (or as
# specified by the <tt>:batch_size</tt> option).
#
# Example:
#
# Person.find_each(:conditions => "age > 21") do |person|
# person.party_all_night!
# end
#
# Note: This method is only intended to use for batch processing of
# large amounts of records that wouldn't fit in memory all at once. If
# you just need to loop over less than 1000 records, it's probably
# better just to use the regular find methods.
def find_each(options = {})
find_in_batches(options) do |records|
records.each { |record| yield record }
end
self
end
# Yields each batch of records that was found by the find +options+ as
# an array. The size of each batch is set by the <tt>:batch_size</tt>
# option; the default is 1000.
#
# You can control the starting point for the batch processing by
# supplying the <tt>:start</tt> option. This is especially useful if you
# want multiple workers dealing with the same processing queue. You can
# make worker 1 handle all the records between id 0 and 10,000 and
# worker 2 handle from 10,000 and beyond (by setting the <tt>:start</tt>
# option on that worker).
#
# It's not possible to set the order. That is automatically set to
# ascending on the primary key ("id ASC") to make the batch ordering
# work. This also mean that this method only works with integer-based
# primary keys. You can't set the limit either, that's used to control
# the the batch sizes.
#
# Example:
#
# Person.find_in_batches(:conditions => "age > 21") do |group|
# sleep(50) # Make sure it doesn't get too crowded in there!
# group.each { |person| person.party_all_night! }
# end
def find_in_batches(options = {})
raise "You can't specify an order, it's forced to be #{batch_order}" if options[:order]
raise "You can't specify a limit, it's forced to be the batch_size" if options[:limit]
start = options.delete(:start).to_i
batch_size = options.delete(:batch_size) || 1000
with_scope(:find => options.merge(:order => batch_order, :limit => batch_size)) do
records = find(:all, :conditions => [ "#{table_name}.#{primary_key} >= ?", start ])
while records.any?
yield records
break if records.size < batch_size
records = find(:all, :conditions => [ "#{table_name}.#{primary_key} > ?", records.last.id ])
end
end
end
private
def batch_order
"#{table_name}.#{primary_key} ASC"
end
end
end
end
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