title: Pydantic add field to model after a model validation (add filed to incoming model)
body: <p>I have an incoming pydantic User model.
  To add field after validation I'm converting it to dict and adding a field like for a regular dict.</p>
  <pre><code>user = employee.dict()
  user.update({'invited_by': 'some_id'})
  db.save(user)
  </code></pre>
  <p>Is there a shorter AND CLEANEST way to add a field? Because even for myself it's no such clear, every time that I meeting this code (that wrote by myself) I thinking &quot;Why I'm converting model to dict as separate instruction/line if I can do it inside <code>save</code> function (<code>db.save(user)</code>)</p>