ActiveRecord Breakout Code Notes

ar-associations.rb

# id | user_id
class Profile
  belongs_to :user

  # is actually:
  # def user
  #   User.find_by(id: self.user_id)
  # end
end

# id
class User
  has_one :profile

  # is actually:
  # def profile
  #   Profile.find_by(user_id: self.id)
  # end

  has_many :posts, foreign_key: 'author_id'

  # is actually:
  # def posts
  #   Post.where(author_id: self.id)
  # end

  has_many :comments, foreign_key: 'commenter_id'

  # is actually:
  # def comments
  #   Comment.where(commenter_id: self.id)
  # end

  has_many :post_comments, through: :posts, source: :comments

  # is actually:
  # def post_comments
  #   self.posts.map {|p| p.comments }
  # end
end

# id | author_id
class Post
  belongs_to :author, class_name: 'User'

  # is actually:
  # def author
  #   User.find_by(id: self.author_id)
  # end

  has_many :comments

  # is actually:
  # def comments
  #   Comment.where(post_id: self.id)
  # end
end

# id | post_id | commenter_id
class Comment
  belongs_to :post

  # is actually:
  # def post
  #   Post.find_by(id: self.post_id
  # end

  belongs_to :commenter, class_name: 'User'

  # is actually:
  # def commenter
  #   User.find_by(id: self.commenter_id)
  # end

  # conceptually equivalent to belongs_to :through (which doesn't exist)
  def post_author
    post.author
  end
end

ar-validations.rb

id | name | email | age | password_hash
class User
  MAX_AGE = 130

  # name must exist
  validates :name, presence: true
  # email must exist and be in the right format
  validates :email, format: { with: /.+\@.+\..+/, message: 'is not in the correct format' }, uniqueness: true
  # age must be a number but doesn't have to exist, but must also be in the possible ages of humans
  validates :age, numericality: { only_integer: true }, inclusion: { in: (0..MAX_AGE), message: 'is not a human age' }
  # password hash must exist
  validates :password_hash, presence: true

  # if a user is over the age of 15, they must have an email
  validate :age_must_have_email

  private

  def age_must_have_email
    if age > 15 && email.empty?
      errors.add(:email, 'must be present when over the age of 15')
    end
  end
end