Response to James Coglan's 'An ActiveRecord conumdrum': https://gist.github.com/jcoglan/4ccf434cd2e1305d1c5c

awaiting_moderation_test.rb

require 'active_record'
require 'logger'
require 'minitest/autorun'

ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :texts do |t|
    t.string :title
    t.text :body
  end

  create_table :quotes do |t|
    t.text :body
    t.string :source
    t.string :url
  end

  create_table :links do |t|
    t.string :title
    t.string :url
  end

  create_table :users do |t|
    t.string :username
  end

  create_table :blogs do |t|
    t.belongs_to :user
    t.string :title
  end

  create_table :posts do |t|
    t.timestamps
    t.belongs_to :blog
    t.belongs_to :content, polymorphic: true
  end

  create_table :comments do |t|
    t.timestamps
    t.belongs_to :user
    t.belongs_to :post
    t.text :body
    t.boolean :accepted
  end
end

class User < ActiveRecord::Base
  has_many :blogs
  has_many :comments
  has_many :blog_comments, through: :blogs, source: :comments
end

class Blog < ActiveRecord::Base
  belongs_to :user
  has_many :posts
  has_many :comments, through: :posts
end

class Post < ActiveRecord::Base
  belongs_to :blog
  belongs_to :content, polymorphic: true
  has_many :comments
end

module Content
  extend ActiveSupport::Concern

  included do
    has_many :posts, as: :content
    has_many :comments, through: :posts
  end
end

class Text < ActiveRecord::Base; include Content; end
class Quote < ActiveRecord::Base; include Content; end
class Link < ActiveRecord::Base; include Content; end

class Comment < ActiveRecord::Base
  belongs_to :user
  belongs_to :post
  has_one :blog, through: :post

  def self.for_blog_author(author)
    joins(:blog).where(blogs: { user_id: author.id })
  end

  def self.for_moderation
    where(accepted: nil)
  end
end

alice = User.create(username: 'alice')
bob   = User.create(username: 'bob')
blog  = alice.blogs.create(title: 'Not even once')

text_entry = Text.create(
  title: 'How to bulk update a MySQL table',
  body:  'First, delete all your indexes.'
)

quote_entry = Quote.create(
  body:   'There are two hard things in computer science: MySQL consistency.',
  source: 'CSS Perverts',
  url:    'https://medium.com/could-you-not'
)

link_entry = Link.create(
  title: 'Web development that does not always hurt',
  url:   'http://rubyonrails.org/'
)

text_post = Post.create(blog: blog, content: text_entry)
quote_post = Post.create(blog: blog, content: quote_entry)
link_post = Post.create(blog: blog, content: link_entry)

Comment.create(
  user:     bob,
  post:     text_post,
  body:     'This sounds like a lot of work.'
)

Comment.create(
  user:     bob,
  post:     text_post,
  body:     '4 hours later and I am still at my computer. Help!'
)

Comment.create(
  user:     bob,
  post:     quote_post,
  body:     'Never were truer words spoken. Such thought leadership.'
)

class TestMe < MiniTest::Unit::TestCase
  def setup
    @alice = User.find_by_username!('alice')
  end

  def test_awaiting_moderation_count
    assert_equal 3, Comment.for_blog_author(@alice).for_moderation.count
    assert_equal 3, @alice.blog_comments.for_moderation.count
  end
end