How to hire Ruby on Rails developers (12 questions for a job interview)

In another post, I was documenting some of the interview questions that I think are important to us when we are trying to hire iOS developers. In this case, I'm going to expose some questions for an interview for Ruby on Rails developers.

Ruby language

1. What is the difference between a class and a module?
2. What are the three levels of method access control for classes and what do they mean?
3. What does "self" mean?
4. Explain what singleton methods are. What is Eigenclass in Ruby?
5. What is the difference between false and nil in Ruby?

Rails Framework

1. What is the Asset Pipeline?
2. Explain the "Active record" pattern.
3. What is a Polymorphic Association in Rails?
4. Explain the difference between optimistic and pessimistic locking in Rails.

Security

1. What is the CSRF? How do Rails protect an application against this security flaw?
2. How should we store insecure data such as passwords?
3. Why do we need to use HTTPS instead of HTTP?

Let me know what other questions you would use for an interview to hire Ruby on Rails developers.