client.rb

#!/usr/bin/ruby

require "uri"
require "net/http"
require "json"

module API
  def self.start(url)
    parse(get(url))
  end

  def self.get(url)
    #$stderr.puts "GET: #{url}"
    Net::HTTP.get(URI(url))
  end

  def self.parse(json)
    JSON.parse(json, options)
  end

  def self.options
    {
      symbolize_names: true,
      object_class: Object,
      array_class: Array
    }
  end

  class Object < ::Hash
    def method_missing(key, *args)
      u = "#{key}_url".to_sym

      if include?(u)
        API.start(self[u])

      elsif include?(key)
        self[key]

      else
        super

      end
    end
  end

  class Array < ::Array
  end
end

demo.rb

#!/usr/bin/ruby

require "./client"

api = API.start("http://localhost:4567")

puts api.blogs.first.name
# => My Favorite Photos of Cats

puts api.blogs.first.posts.last.title
# => Look at this hilarious cat

puts api.blogs.first.posts.last.author.username
# => adammck

puts api.blogs.first.posts.last.full.body
# => ...

puts api.blogs.first.posts.last.author.posts.first.title
# => Welcome to my cat blog

Gemfile

source "https://rubygems.org"

gem "sinatra"
gem "sinatra-contrib"
gem "sequel"
gem "sqlite3"
gem "multi_json"

group :development do
  gem "shotgun"
  gem "thin"
end

server.rb

#!/usr/bin/ruby

require "sequel"
require "sinatra"
require "multi_json"
require "sinatra/json"

DB = Sequel.sqlite

# ------------------------------------------------------------------------------

DB.create_table :users do
  primary_key :id
  String :username
  String :email
  String :real_name
end

DB.create_table :blogs do
  primary_key :id
  String :name
end

DB.create_table :posts do
  primary_key :id
  foreign_key :blog_id, :blogs
  foreign_key :author_id, :users
  String :title
  String :body
end

# ------------------------------------------------------------------------------

DB[:users].tap do |t|
  t.insert id: 1, username: "adammck", email: "[email protected]", real_name: "Adam Mckaig"
end

DB[:blogs].tap do |t|
  t.insert id: 1, name: "My Favorite Photos of Cats"
  t.insert id: 2, name: "My Serious Work Blog"
end

DB[:posts].tap do |t|
  t.insert id: 1, blog_id: 1, author_id: 1, title: "Welcome to my cat blog",     body: "..."
  t.insert id: 2, blog_id: 1, author_id: 1, title: "OMG this cat is so funny",   body: "..."
  t.insert id: 3, blog_id: 1, author_id: 1, title: "Look at this hilarious cat", body: "..."
end

# ------------------------------------------------------------------------------

def user_as_json(user)
  {
    username: user[:username],
    email: user[:email],
    real_name: user[:real_name],
    self_url: url("/users/#{user[:id]}"),
    posts_url: url("/users/#{user[:id]}/posts"),
    blogs_url: url("/users/#{user[:id]}/blogs")
  }
end

def blog_as_json(blog)
  {
    name: blog[:name],
    self_url: url("/blogs/#{blog[:id]}"),
    posts_url: url("/blogs/#{blog[:id]}/posts"),
  }
end

def short_post_as_json(post)
  {
    title: post[:title],
    full_url: url("/posts/#{post[:id]}"),
    author_url: url("/users/#{post[:author_id]}")
  }
end

def full_post_as_json(post)
  {
    title: post[:title],
    body: post[:body],
    self_url: url("/posts/#{post[:id]}"),
    author_url: url("/users/#{post[:author_id]}")
  }
end

# ------------------------------------------------------------------------------

get "/" do
  json({
    users_url: url("/users"),
    blogs_url: url("/blogs")
  })
end

get "/users" do
  json(DB[:users].map do |user|
    user_as_json(user)
  end)
end

get "/users/:id" do
  json(user_as_json(DB[:users][id: params[:id]]))
end

get "/users/:id/posts" do
  json(DB[:posts].where(author_id: params[:id]).map do |post|
    short_post_as_json(post)
  end)
end

get "/blogs" do
  json(DB[:blogs].map do |blog|
    blog_as_json(blog)
  end)
end

get "/blogs/:id" do
  json(blog_as_json(DB[:blogs][id: params[:id]]))
end

get "/blogs/:id/posts" do
  json(DB[:posts].where(blog_id: params[:id]).map do |post|
    short_post_as_json(post)
  end)
end

get "/posts" do
  json(DB[:posts].map do |post|
    short_post_as_json(post)
  end)
end

get "/posts/:id" do
  json(full_post_as_json(DB[:posts][id: params[:id]]))
end