class ActiveRecord::Batches::BatchEnumerator

def update_all(updates)

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

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

Updates records in batches. Returns the total number of rows affected. 
def update_all(updates)
  sum do |relation|
    relation.update_all(updates)
  end
end