# module ActiveRecord::Batches

### Constants

ORDER_IGNORE_MESSAGE

### Public Instance Methods

find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil) { |record| ... } click to toggle source

Looping through a collection of records from the database (using the ActiveRecord::Scoping::Named::ClassMethods#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. Defaults to 1000.

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

- `:finish` - Specifies the primary key value to end at, inclusive of the value.

- `:error_on_ignore` - Overrides the application config to specify if an error should be raised when an order is present in the relation.

Limits are honored, and if present there is no requirement for the batch size: it can be less than, equal to, or greater than the limit.

The options `start` and `finish` are especially useful if you want multiple workers dealing with the same processing queue. You can make worker 1 handle all the records between id 1 and 9999 and worker 2 handle from 10000 and beyond by setting the `:start` and `:finish` option on each worker.

    # Let's process from record 10_000 on.
    Person.find_each(start: 10_000) 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: By its nature, batch processing is subject to race conditions if other processes are modifying the database.

    # File lib/active_record/relation/batches.rb, line 60
    def find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil)
      if block_given?
        find_in_batches(start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore) do |records|
          records.each { |record| yield record }
        end
      else
        enum_for(:find_each, start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore) do
          relation = self
          apply_limits(relation, start, finish).size
        end
      end
    end

find_in_batches(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil) { |to_a| ... } 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. Defaults to 1000.

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

- `:finish` - Specifies the primary key value to end at, inclusive of the value.

- `:error_on_ignore` - Overrides the application config to specify if an error should be raised when an order is present in the relation.

Limits are honored, and if present there is no requirement for the batch size: it can be less than, equal to, or greater than the limit.

The options `start` and `finish` are especially useful if you want multiple workers dealing with the same processing queue. You can make worker 1 handle all the records between id 1 and 9999 and worker 2 handle from 10000 and beyond by setting the `:start` and `:finish` option on each worker.

    # Let's process from record 10_000 on.
    Person.find_in_batches(start: 10_000) 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: By its nature, batch processing is subject to race conditions if other processes are modifying the database.

    # File lib/active_record/relation/batches.rb, line 119
    def find_in_batches(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil)
      relation = self
      unless block_given?
        return to_enum(:find_in_batches, start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore) do
          total = apply_limits(relation, start, finish).size
          (total - 1).div(batch_size) + 1
        end
      end

      in_batches(of: batch_size, start: start, finish: finish, load: true, error_on_ignore: error_on_ignore) do |batch|
        yield batch.to_a
      end
    end

in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore: nil) { |yielded_relation| ... } click to toggle source

Yields ActiveRecord::Relation objects to work with a batch of records.

    Person.where("age > 21").in_batches do |relation|
      relation.delete_all
      sleep(10) # Throttle the delete queries
    end

If you do not provide a block to in_batches, it will return a BatchEnumerator which is enumerable.

    Person.in_batches.each_with_index do |relation, batch_index|
      puts "Processing relation ##{batch_index}"
      relation.delete_all
    end

Examples of calling methods on the returned BatchEnumerator object:

    Person.in_batches.delete_all
    Person.in_batches.update_all(awesome: true)
    Person.in_batches.each_record(&:party_all_night!)

#### Options¶ ↑

- `:of` - Specifies the size of the batch. Defaults to 1000.

- `:load` - Specifies if the relation should be loaded. Defaults to false.

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

- `:finish` - Specifies the primary key value to end at, inclusive of the value.

- `:error_on_ignore` - Overrides the application config to specify if an error should be raised when an order is present in the relation.

Limits are honored, and if present there is no requirement for the batch size, it can be less than, equal, or greater than the limit.

The options `start` and `finish` are especially useful if you want multiple workers dealing with the same processing queue. You can make worker 1 handle all the records between id 1 and 9999 and worker 2 handle from 10000 and beyond by setting the `:start` and `:finish` option on each worker.

    # Let's process from record 10_000 on.
    Person.in_batches(start: 10_000).update_all(awesome: true)

An example of calling where query method on the relation:

    Person.in_batches.each do |relation|
      relation.update_all('age = age + 1')
      relation.where('age > 21').update_all(should_party: true)
      relation.where('age <= 21').delete_all
    end

NOTE: If you are going to iterate through each record, you should call each_record on the yielded BatchEnumerator:

    Person.in_batches.each_record(&:party_all_night!)

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 consistent. Therefore the primary key must be orderable, e.g. an integer or a string.

NOTE: By its nature, batch processing is subject to race conditions if other processes are modifying the database.

    # File lib/active_record/relation/batches.rb, line 194
    def in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore: nil)
      relation = self
      unless block_given?
        return BatchEnumerator.new(of: of, start: start, finish: finish, relation: self)
      end

      if arel.orders.present?
        act_on_ignored_order(error_on_ignore)
      end

      batch_limit = of
      if limit_value
        remaining   = limit_value
        batch_limit = remaining if remaining < batch_limit
      end

      relation = relation.reorder(batch_order).limit(batch_limit)
      relation = apply_limits(relation, start, finish)
      batch_relation = relation

      loop do
        if load
          records = batch_relation.records
          ids = records.map(&:id)
          yielded_relation = where(primary_key => ids)
          yielded_relation.load_records(records)
        else
          ids = batch_relation.pluck(primary_key)
          yielded_relation = where(primary_key => ids)
        end

        break if ids.empty?

        primary_key_offset = ids.last
        raise ArgumentError.new("Primary key not included in the custom select clause") unless primary_key_offset

        yield yielded_relation

        break if ids.length < batch_limit

        if limit_value
          remaining -= ids.length

          if remaining == 0
            # Saves a useless iteration when the limit is a multiple of the
            # batch size.
            break
          elsif remaining < batch_limit
            relation = relation.limit(remaining)
          end
        end

        batch_relation = relation.where(arel_attribute(primary_key).gt(primary_key_offset))
      end
    end

### Private Instance Methods

act_on_ignored_order(error_on_ignore) click to toggle source

    # File lib/active_record/relation/batches.rb, line 262
    def act_on_ignored_order(error_on_ignore)
      raise_error = (error_on_ignore.nil? ? klass.error_on_ignored_order : error_on_ignore)

      if raise_error
        raise ArgumentError.new(ORDER_IGNORE_MESSAGE)
      elsif logger
        logger.warn(ORDER_IGNORE_MESSAGE)
      end
    end

apply_limits(relation, start, finish) click to toggle source

    # File lib/active_record/relation/batches.rb, line 252
    def apply_limits(relation, start, finish)
      relation = relation.where(arel_attribute(primary_key).gteq(start)) if start
      relation = relation.where(arel_attribute(primary_key).lteq(finish)) if finish
      relation
    end

batch_order() click to toggle source

    # File lib/active_record/relation/batches.rb, line 258
    def batch_order
      "#{quoted_table_name}.#{quoted_primary_key} ASC"
    end