Please rate your experience and skills with the listed technologies on a ten-point scale.

We've came up with few complex (and not so) tasks to reveal your skills. Attach an answer to each of them in the form below. Hopefully they will bring you as much pleasure as they bring us.
(Language — Ruby on Rails)

class User < ApplicationRecord
  has_one :address
end

class Address < ApplicationRecord
  belongs_to :user
end

v1 = true and false
v2 = true && false

What can you use as keys for Hash data structure in ruby?

User is linked with organization through members table. Does this method look good?

def invite_user_to_organization(organization, user_params)
  user = User.create(user_params)

  if user.persisted?
    organization.members.create(user_id: user.id)
    UserMailer.notify_about_new_membership(user)
  end

  user
end

Let's imagine you're working on mailing list service and you are writing code which should send newsletter to all emails except unsubscribed. Does this implementation look good?
mailing_list = ['john@foo', 'alice@bar', ...]
unsubscribed_emails = ['alice@buz', ...]

unsubscribed_emails.each { |email| mailing_list.delete(email) }

send_newsletter(mailing_list)

We don't want to expose real IDs of ActiveRecord models in public so we want to add column "token" to each model and invent solution to generate unique tokens randomly. Please write short implementation which can illustrate your possible solution.

Let's imagine that you need to create service which allows user to set timestamp and message to be notified by email or sms in the given moment of time in future. How would you implement it?