author.rb

class Post
  include Cequel::Record
  
  belongs_to :blog
  key :id, :timeuuid, auto: true
  column :author_id, :timeuuid
  # other column definitions
  
  def author
    @author ||= User.find(author_id)
  end
  
  def author=(author)
    @author = author
    self.author_id = author.id
  end
end

user.rb

class User
  include Cequel::Record
  
  key :id, :timeuuid, auto: true
  column :username, :text
  # other column definitions
  
  def posts
    @posts ||= Post.where(author_id: id)
  end
end