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Methods
F
Instance Public methods
find_each(begin_at: nil, end_at: nil, batch_size: 1000, start: nil)

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

  • :batch_size - Specifies the size of the batch. Default to 1000.

  • :begin_at - Specifies the primary key value to start from, inclusive of the value.

  • :end_at - Specifies the primary key value to end at, inclusive of the value.

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 :begin_at and :end_at option on each worker).

# Let's process for a batch of 2000 records, skipping the first 2000 rows
Person.find_each(begin_at: 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 when the primary key is orderable (e.g. an integer or string).

NOTE: You can't set the limit either, that's used to control the batch sizes.

# File activerecord/lib/active_record/relation/batches.rb, line 49
    def find_each(begin_at: nil, end_at: nil, batch_size: 1000, start: nil)
      if start
        begin_at = start
        ActiveSupport::Deprecation.warn("            Passing `start` value to find_each is deprecated, and will be removed in Rails 5.1.
            Please pass `begin_at` instead.
".squish)
      end
      if block_given?
        find_in_batches(begin_at: begin_at, end_at: end_at, batch_size: batch_size) do |records|
          records.each { |record| yield record }
        end
      else
        enum_for(:find_each, begin_at: begin_at, end_at: end_at, batch_size: batch_size) do
          relation = self
          apply_limits(relation, begin_at, end_at).size
        end
      end
    end
find_in_batches(begin_at: nil, end_at: nil, batch_size: 1000, start: nil)

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

If you do not provide a block to find_in_batches, it will return an Enumerator for chaining with other methods:

Person.find_in_batches.with_index do |group, batch|
  puts "Processing group ##{batch}"
  group.each(&:recover_from_last_night!)
end

To be yielded each record one by one, use find_each instead.

Options

  • :batch_size - Specifies the size of the batch. Default to 1000.

  • :begin_at - Specifies the primary key value to start from, inclusive of the value.

  • :end_at - Specifies the primary key value to end at, inclusive of the value.

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 :begin_at and :end_at option on each worker).

# Let's process the next 2000 records
Person.find_in_batches(begin_at: 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 when the primary key is orderable (e.g. an integer or string).

NOTE: You can't set the limit either, that's used to control the batch sizes.

# File activerecord/lib/active_record/relation/batches.rb, line 108
    def find_in_batches(begin_at: nil, end_at: nil, batch_size: 1000, start: nil)
      if start
        begin_at = start
        ActiveSupport::Deprecation.warn("            Passing `start` value to find_in_batches is deprecated, and will be removed in Rails 5.1.
            Please pass `begin_at` instead.
".squish)
      end

      relation = self
      unless block_given?
        return to_enum(:find_in_batches, begin_at: begin_at, end_at: end_at, batch_size: batch_size) do
          total = apply_limits(relation, begin_at, end_at).size
          (total - 1).div(batch_size) + 1
        end
      end

      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

      relation = relation.reorder(batch_order).limit(batch_size)
      relation = apply_limits(relation, begin_at, end_at)
      records = relation.to_a

      while records.any?
        records_size = records.size
        primary_key_offset = records.last.id
        raise "Primary key not included in the custom select clause" unless primary_key_offset

        yield records

        break if records_size < batch_size

        records = relation.where(table[primary_key].gt(primary_key_offset)).to_a
      end
    end