Epigene

  def with_characteristics?(characteristics_hash)
    author.name == characteristics_hash[:author_name] &&
      publisher.name == characteristics_hash[:publisher_name]
  end

Epigene

describe "FactoryGirl.build_stubbed VS [FactoryGirl.build, FactoryGirl.create]" do
  subject { book.with_characteristics?(options) }

  let(:options) { {author_name: book.author.name, publisher_name: book.publisher.name} }

  bout3_number_of = 200

  context "when setting up with FactoryGirl.build_stubbed" do
    let(:book) { build_stubbed(:book) }

Epigene

describe "#instance_double VS FactoryGirl.build_stubbed, FactoryGirl.build, and FactoryGirl.create" do
  subject { book.by_bce_autor? }

  bout2_number_of = 200

  context "when setting up with #instance_double" do
    let(:book) { build_stubbed(:book) }
    let(:author) { instance_double("Author", bce?: true) }

    before { allow(book).to receive(:author).and_return(author) }

Epigene

  def by_bce_autor?
    author.bce?
  end

Epigene

describe "#new VS all others when testing Book#vampire_title?" do
  subject { book.vampire_title? }

  bout1_number_of = 200

  context "when setting up with #new" do
    bout1_number_of.times do
      let(:book) { Book.new(title: "Vampire Literature, a Historical Perspective") }

      it { is_expected.to eq(true) }

Epigene

  def vampire_title?
    title.to_s.match?(%r'vamp[iy]re'i)
  end

Epigene

# from https://stackoverflow.com/a/123481/3319298
# Uses LEFT JOIN to join the posts table with itself in a clever manner - on id AND the relevant, :created_at row.
# The check on created_at makes it so that the last records have NULLs in t2 rows, so we use WHERE to select those and done.
scope :users_last_posts, -> {

  query = <<~HEREDOC
    SELECT t1.id
    FROM post t1
    LEFT OUTER JOIN posts t2
      ON t1.author_id = t2.author_id AND

Epigene

last_post_ids = Post.select("MAX(id) AS last_post_id").group(:user_id)
  
last_posts = Post.where(id: last_post_ids).order(created_at: :desc)

Epigene

last_post_ids = []
User.where(id: Post.all.distinct.pluck(:user_id)).find_each |user|
  last_post_ids << user.posts.order(created_at: :desc).limit(1).pluck(:id).last
end

last_posts = Post.where(id: last_post_ids).order(created_at: :desc)

Epigene

last_posts = []
User.all.each |user|
  last_posts << user.posts.order(created_at: :asc).last
end

# oops, some users have no posts and the array has nils
last_posts = last_posts.compact

# now to have them in correct order
last_posts = last_posts.sort{ |x, y| y.created_at <=> x.created_at }