in_batches

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.

• :order - Specifies the primary key order (can be :asc or :desc or an array consisting of :asc or :desc). Defaults to :asc.

  class Order < ActiveRecord::Base
    self.primary_key = [:id_1, :id_2]
  end
  
  Order.in_batches(order: [:asc, :desc])
  

  In the above code, id_1 is sorted in ascending order and id_2 in descending order.

• :use_ranges - Specifies whether to use range iteration (id >= x AND id <= y). It can make iterating over the whole or almost whole tables several times faster. Only whole table iterations use this style of iteration by default. You can disable this behavior by passing false. If you iterate over the table and the only condition is, e.g., archived_at: nil (and only a tiny fraction of the records are archived), it makes sense to opt in to this approach.

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: Order can be ascending (:asc) or descending (:desc). It is automatically set to ascending on the primary key (“id ASC”). 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.