How can I run updates in batches in Rails 3/4?

Question

I need to mass-update many thousands of records, and I would like to process the updates in batches. First, I tried:

Foo.where(bar: \'bar\').find_in_batches.upda         


        

Answer 1

pdobb's answer is on the right track, but didn't work for me in Rails 3.2.21 because of this issue of ActiveRecord not parsing OFFSET with UPDATE calls:

https://github.com/rails/rails/issues/10849

I modified the code accordingly and it worked fine for concurrently setting the default value on my Postgres table:

batch_size = 1000
0.step(Foo.count, batch_size).each do |offset|
  Foo.where('id > ? AND id <= ?', offset, offset + batch_size).
      order(:id).
      update_all(foo: 'bar')
end