title: Control object creation flow in Django inheritance models
body: <p>I have been read some Django document about inheritance models and <code>parent_link</code>. 
  Suppose that I have these models: </p>
  
  <pre><code>class Parent(models.Model):
      #Some field goes here! 
  class Child(Parent):
      #Some field goes here! 
  </code></pre>
  
  <p>I have 3 questions about this pattern: </p>
  
  <ol>
  <li><p>What should I do if I want to create new child object and pass id of existing parent to that? </p></li>
  <li><p>What should I do if I want to create just new child object  and after a while create parent object for that child? </p></li>
  <li>Also I din't understand this document about <code>parent_link</code>: 
  
  <blockquote>
    <p><strong>OneToOneField.parent_link</strong></p>
    
    <p>When True and used in a model which inherits from another concrete
    model, indicates that this field should be used as the link back to
    the parent class, rather than the extra OneToOneField which would
    normally be implicitly created by subclassing.</p>
  </blockquote></li>
  </ol>
  
  <p>Thanks for your help!</p>
  
  <p><strong>Update Question</strong>
  Suppose these models: </p>
  
  <pre><code>class User(AbsteractBaseUser):
      #Some field goes here! 
  
  class Student(User):
      #Some field goes here! 
  
  class Teacher(User):
      #Some field goes here! 
  
  class Employee(User):
      #Some field goes here! 
  </code></pre>
  
  <ol start="4">
  <li>Is it possible to create <code>Teacher</code> object and put the pk of existing <code>User</code> object for that teacher? </li>
  </ol>