Challenge 1: A JSON Index Action — Solution

# app/controllers/comments_controller.rb
class CommentsController < ApplicationController
  def index
    comments = Comment.all
    render json: comments
  end

  def create
    comment = Comment.new(comment_params)
    if comment.save
      render json: comment, status: :created
    else
      render json: { errors: comment.errors }, status: :unprocessable_entity
    end
  end

  private

  def comment_params
    params.require(:comment).permit(:body, :post_id)
  end
end

=begin
Notes:
- render json: comments on the collection serializes every Comment in the
  relation the same way render json: comment (singular) would serialize one
  -- Rails calls .to_json across the whole array automatically.
- status: :created is the symbol form of HTTP 201, matching what a
  successful POST should return per REST convention (the same convention
  express1-7 covered numerically).
- On failure, comment.errors is rendered directly as JSON under an errors
  key, giving the client the same validation-failure detail rails1-8's
  strong-parameters chapter surfaced through form re-rendering -- just
  shaped as JSON instead of HTML.
- comment_params reuses the exact strong-parameters pattern from rails1-8 --
  require(:comment).permit(...) -- unchanged by the fact this is an API
  action rather than an HTML form submission.
=end