ar_lazy_preload example (for graphql without N+1 issues)

ar_lazy_preload_example.rb

# Config
require 'rails'
require 'ar_lazy_preload' # https://github.com/DmitryTsepelev/ar_lazy_preload
require 'active_record'
ActiveRecord::Base.establish_connection adapter: 'sqlite3', database: ':memory:'

# not sure where this is supposed to happen, but it's necessary b/c ar_lazy_preload
# adds its functionality in a callback after active record finishes loading.
ArLazyPreload::Railtie.config.to_prepare_blocks.each(&:call)

# Schema
ActiveRecord::Schema.define do
  self.verbose = false
  
  create_table :users do |t|
    t.string :name
  end
  
  create_table :posts do |t|
    t.string :name
    t.integer :user_id
  end

  create_table :comments do |t|
    t.string :body
    t.integer :post_id
  end
end

# Models
class User < ActiveRecord::Base
  has_many :posts
end

class Post < ActiveRecord::Base
  belongs_to :user
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

# Seed Data
user = User.create! name: 'Josh'
post1, post2 = user.posts = [Post.new(name: 'yo ho ho'), Post.new(name: 'and a bottle of rum')]
post1.comments.create! body: 'a pirate!'
post1.comments.create! body: 'blow the man down!'
post2.comments.create! body: 'or whiskey!'

user = User.create! name: 'Jan'
post, * = user.posts = [Post.new(name: 'Grape Jelly 4 lyfe!')]
post.comments.create! body: 'jan likes jam!'

# Helper Functions
def self.capture_queries(&block)
  queries = []
  capturer = -> *, data { queries << data.values_at(:name, :sql).select(&:present?).join(": ") }
  ActiveSupport::Notifications.subscribed capturer, "sql.active_record", &block
  queries
end

# ===== Examples =====

# Only loads users, b/c did not try to access posts
capture_queries do
  User
    .all
    .lazy_preload(posts: :comments)
    .map(&:name) # => ["Josh", "Jan"]
end
# => ["User Load: SELECT \"users\".* FROM \"users\""]

# Only loads users, and posts, b/c did not try to access comments
capture_queries do
  User
    .all
    .lazy_preload(posts: :comments)
    .map do |u|
    { name: u.name,
      posts: u.posts.map { |p| p.name },
    }
  end
  # => [{:name=>"Josh", :posts=>["yo ho ho", "and a bottle of rum"]},
  #     {:name=>"Jan", :posts=>["Grape Jelly 4 lyfe!"]}]
end
# => ["User Load: SELECT \"users\".* FROM \"users\"",
#     "Post Load: SELECT \"posts\".* FROM \"posts\" WHERE \"posts\".\"user_id\" IN (?, ?)"]

# Loads users, posts, and comments, b/c accessed all of them
capture_queries do
  User
    .all
    .lazy_preload(posts: :comments)
    .map do |u|
    { name: u.name,
      posts: u.posts.map { |p|
        { name: p.name, comments: p.comments.map(&:body) }
      },
    }
  end
  # => [{:name=>"Josh",
  #      :posts=>
  #       [{:name=>"yo ho ho", :comments=>["a pirate!", "blow the man down!"]},
  #        {:name=>"and a bottle of rum", :comments=>["or whiskey!"]}]},
  #     {:name=>"Jan",
  #      :posts=>
  #       [{:name=>"Grape Jelly 4 lyfe!", :comments=>["jan likes jam!"]}]}]
end
# => ["User Load: SELECT \"users\".* FROM \"users\"",
#     "Post Load: SELECT \"posts\".* FROM \"posts\" WHERE \"posts\".\"user_id\" IN (?, ?)",
#     "Comment Load: SELECT \"comments\".* FROM \"comments\" WHERE \"comments\".\"post_id\" IN (?, ?, ?)"]