# File activerecord/lib/active_record/relation/batches/batch_enumerator.rb, line 49
def delete_all
  sum(&:delete_all)
end

Deletes records in batches. Returns the total number of rows affected.

Person.in_batches.delete_all

See Relation#delete_all for details of how each batch is deleted.

# File activerecord/lib/active_record/relation/batches/batch_enumerator.rb, line 69
def destroy_all
  each(&:destroy_all)
end

Destroys records in batches.

Person.where("age < 10").in_batches.destroy_all

See Relation#destroy_all for details of how each batch is destroyed.

# File activerecord/lib/active_record/relation/batches/batch_enumerator.rb, line 78
def each
  enum = @relation.to_enum(:in_batches, of: @of, start: @start, finish: @finish, load: false)
  return enum.each { |relation| yield relation } if block_given?
  enum
end

Yields an ActiveRecord::Relation object for each batch of records.

Person.in_batches.each do |relation|
  relation.update_all(awesome: true)
end

# File activerecord/lib/active_record/relation/batches/batch_enumerator.rb, line 36
def each_record
  return to_enum(:each_record) unless block_given?

  @relation.to_enum(:in_batches, of: @of, start: @start, finish: @finish, load: true).each do |relation|
    relation.records.each { |record| yield record }
  end
end

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.

Person.in_batches.each_record do |person|
  person.do_awesome_stuff
end

Person.where("age > 21").in_batches(of: 10).each_record do |person|
  person.party_all_night!
end

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

Person.in_batches.each_record.with_index do |person, index|
  person.award_trophy(index + 1)
end

# File activerecord/lib/active_record/relation/batches/batch_enumerator.rb, line 58
def update_all(updates)
  sum do |relation|
    relation.update_all(updates)
  end
end

Updates records in batches. Returns the total number of rows affected.

Person.in_batches.update_all("age = age + 1")

See Relation#update_all for details of how each batch is updated.