title: SQL + Rails - is it posible to get a collection of objects with the values of attributes from other table columns
body: <pre><code>class Baby
    belongs_to :child
    attr :is_public
    scope :public, includes(:child).merge(Child.public).where('babies.is_public IS TRUE')
  end
  
  class Child
    belongs_to :parent
    attr :is_public
  
    scope: public, where ???
    def is_public; read_attribute(:is_public).blank? ? self.parent.is_public : super(); end
  end
  
  class Parent
    has_many :children
    attr :is_public
  end
  </code></pre>
  
  <p>Is it possible to get a collection of objects of Child 
    where if the value of attribute_a of child is NULL 
    it should get the value from parents.attribute_a 
  in one sql statement</p>