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module ActiveRecord
module Batches
# Looping through a collection of records from the database
# (using the +all+ method, for example) is very inefficient
# since it will try to instantiate all the objects at once.
#
# In that case, batch processing methods allow you to work
# with the records in batches, thereby greatly reducing memory consumption.
#
# The #find_each method uses #find_in_batches with a batch size of 1000 (or as
# specified by the +:batch_size+ option).
#
# Person.find_each do |person|
# person.do_awesome_stuff
# end
#
# Person.where("age > 21").find_each do |person|
# person.party_all_night!
# end
#
# If you do not provide a block to #find_each, it will return an Enumerator
# for chaining with other methods:
#
# Person.find_each.with_index do |person, index|
# person.award_trophy(index + 1)
# end
#
# ==== Options
# * <tt>:batch_size</tt> - Specifies the size of the batch. Default to 1000.
# * <tt>:start</tt> - Specifies the starting point for the batch processing.
# 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 +:start+ option on that worker).
#
# # Let's process for a batch of 2000 records, skipping the first 2000 rows
# Person.find_each(start: 2000, batch_size: 2000) do |person|
# person.party_all_night!
# end
#
# NOTE: 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 means that this method only works with integer-based
# primary keys.
#
# NOTE: You can't set the limit either, that's used to control
# the batch sizes.
def find_each(options = {})
if block_given?
find_in_batches(options) do |records|
records.each { |record| yield record }
end
else
enum_for :find_each, options
end
end
# Yields each batch of records that was found by the find +options+ as
# an array.
#
# Person.where("age > 21").find_in_batches do |group|
# sleep(50) # Make sure it doesn't get too crowded in there!
# group.each { |person| person.party_all_night! }
# end
#
# ==== Options
# * <tt>:batch_size</tt> - Specifies the size of the batch. Default to 1000.
# * <tt>:start</tt> - Specifies the starting point for the batch processing.
# 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 +:start+ option on that worker).
#
# # Let's process the next 2000 records
# Person.find_in_batches(start: 2000, batch_size: 2000) do |group|
# group.each { |person| person.party_all_night! }
# end
#
# NOTE: 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 means that this method only works with integer-based
# primary keys.
#
# NOTE: You can't set the limit either, that's used to control
# the batch sizes.
def find_in_batches(options = {})
options.assert_valid_keys(:start, :batch_size)
relation = self
if logger && (arel.orders.present? || arel.taken.present?)
logger.warn("Scoped order and limit are ignored, it's forced to be batch order and batch size")
end
start = options.delete(:start)
batch_size = options.delete(:batch_size) || 1000
relation = relation.reorder(batch_order).limit(batch_size)
records = start ? relation.where(table[primary_key].gteq(start)).to_a : relation.to_a
while records.any?
records_size = records.size
primary_key_offset = records.last.id
yield records
break if records_size < batch_size
if primary_key_offset
records = relation.where(table[primary_key].gt(primary_key_offset)).to_a
else
raise "Primary key not included in the custom select clause"
end
end
end
private
def batch_order
"#{quoted_table_name}.#{quoted_primary_key} ASC"
end
end
end
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