Trying to understand arel better.....

arel_help.rb

class Boat < ActiveRecord::Base
  belongs_to  :captain
  has_many    :boat_classifications
  has_many    :classifications, through: :boat_classifications

  def self.first_five
    self.limit(5)
  end

  def self.dinghy
    self.where("length <= ?", 20)
  end

  def self.ship
    self.where("length >?", 20)
  end

  def self.last_three_alphabetically
    order(name: :desc).limit(3)
  end

  def self.without_a_captain
    where(captain: nil)
  end

  def self.sailboats
    joins(:classifications).where(classifications: {name: "Sailboat"})
  end

  def self.with_three_classifications

    where(joins(:classifications).group(:id).having("count(*) = 3"))

  end
  
end