Warmup rails questions

warmup questions.md

1. What is the difference between Ruby’s Hash and ActiveSupport’s HashWithIndifferentAccess?

2. What’s the issue with the controller code below? How would you fix it?

class CommentsController < ApplicationController
  def users_comments
    posts = Post.all
    comments = posts.map(&:comments).flatten
    @user_comments = comments.select do |comment|
      comment.author.username == params[:username]
    end
  end
end

3. How would you define a Person model so that any Person can be assigned as the parent of another Person (as demonstrated in the Rails console below)? What would the migration look like?

irb(main):001:0> john = Person.create(name: "John")
irb(main):002:0> jim = Person.create(name: "Jim", parent: john)
irb(main):003:0> bob = Person.create(name: "Bob", parent: john)
irb(main):004:0> john.children.map(&:name)
=> ["Jim", "Bob"]

4. Suppose we have a Student with id=”4”. If we delete the Student with id=”4”, what will be the result of the following queries:

Student.find(4)
Student.find_by_id(4)