How to fully reload an ActiveRecord to reset it's memoized values?

Question

In an RSpec test, I create a record that has several memoizied values.

foo.reload works as expected for the object's attributes, but memoized ones are still present.

So far, it works by completely recreating the object: foo = Foo.find(123) but in my case, the logic for finding the record is actually more complex.

What's a good, DRY way to fully reload the record and erase all memoized values?

Answer 1

You can do that by redefining reload. For example if you memoized with ||= you can do that:

class Foo < ActiveRecord::Base
  def bar
    @bar ||= rand
  end

  def reload
    @bar = nil
    super
  end
end

For ways to reset all instance variables see Is there a clean API for resetting instance variables on 'reload' in ActiveRecord?

If you use the memoist gem you can call flush_cache there.

Answer 2

The good way is the one you already have: Completely recreating the object.

You cannot "reload" the object's memoized values in any easy "Rails" way, as memoizing attributes isn't a function of Rails or ActiveRecord. Neither knows anything about how you're memoizing methods.

Answer 3

Michael's answer is sound, but be aware that if you use the more sophisticated pattern for also memoization nil and false values, that will NOT reset the memoization.

For instance, using the same example from the article for memoization nil and false values:

def main_address
  return @main_address if defined? @main_address
  @main_address = begin
    main_address = get_home_address_from_api
    main_address ||= get_work_address_from_api
    main_address ||= another_api_call.first
  end
end

This pattern works great because it also memoizes nil and false, but of course, to reset it, it wouldn't be enough to simply set the @main_address to nil, because it would be already be defined and return early.

In these cases, you should reset it like this:

def reset_main_address_memoization
  self.send(:remove_instance_variable, :@main_address) if instance_variable_defined?(:@main_address)
end