module ActiveRecord::Batches - activerecord-4.2.5.2 Documentation

# module ActiveRecord::Batches

### Public Instance Methods

find_each(options = {}) { |record| ... } click to toggle source

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.

- `:start` - 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.

    # File lib/active_record/relation/batches.rb, line 48
    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 do
          options[:start] ? where(table[primary_key].gteq(options[:start])).size : size
        end
      end
    end

find_in_batches(options = {}) { |records| ... } click to toggle source

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.

- `:start` - 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.

    # File lib/active_record/relation/batches.rb, line 98
    def find_in_batches(options = {})
      options.assert_valid_keys(:start, :batch_size)

      relation = self
      start = options[:start]
      batch_size = options[:batch_size] || 1000

      unless block_given?
        return to_enum(:find_in_batches, options) do
          total = start ? where(table[primary_key].gteq(start)).size : 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)
      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
        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

### Private Instance Methods

batch_order() click to toggle source

    # File lib/active_record/relation/batches.rb, line 134
    def batch_order
      "#{quoted_table_name}.#{quoted_primary_key} ASC"
    end