Methods
F
Instance Public methods
find_each(options = {})

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 :batch_size option).

Example:

Person.where("age > 21").find_each 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.

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/batches.rb, line 19
def find_each(options = {})
  find_in_batches(options) do |records|
    records.each { |record| yield record }
  end
end
find_in_batches(options = {})

Yields each batch of records that was found by the find options as an array. The size of each batch is set by the :batch_size option; the default is 1000.

You can control the starting point for the batch processing by supplying the :start 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 :start 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 batch sizes.

Example:

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

Source: show | on GitHub 

# File activerecord/lib/active_record/relation/batches.rb, line 48
def find_in_batches(options = {})
  relation = self

  unless arel.orders.blank? && arel.taken.blank?
    ActiveRecord::Base.logger.warn("Scoped order and limit are ignored, it's forced to be batch order and batch size")
  end

  if (finder_options = options.except(:start, :batch_size)).present?
    raise "You can't specify an order, it's forced to be #{batch_order}" if options[:order].present?
    raise "You can't specify a limit, it's forced to be the batch_size"  if options[:limit].present?

    relation = apply_finder_options(finder_options)
  end

  start = options.delete(:start).to_i
  batch_size = options.delete(:batch_size) || 1000

  relation = relation.reorder(batch_order).limit(batch_size)
  records = relation.where(table[primary_key].gteq(start)).all

  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