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.with_index do |relation, batch_index|
  puts "Processing relation ##{batch_index}"
  relation.each { |relation| 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. Default to 1000.

• :load - Specifies if the relation should be loaded. Default 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

  the order and limit have to be ignored due to batching.
  

This is especially useful if you want to work with the ActiveRecord::Relation object instead of the array of records, or 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 and :finish option on each worker).

# Let's process the next 2000 records
Person.in_batches(of: 2000, start: 2000).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: You can’t set the limit either, that’s used to control the batch sizes.