title: Updating header record or adding line record in one view
body: <p>I have a view that displays <code>HeaderModel</code> details. Under this is displays <code>LineModel</code>s associated with this header.</p>
  
  <p>Some of the <code>LineModel</code> fields are required.</p>
  
  <p>My problem is when it comes to updating the header the <code>ModelState.IsValid</code> is false, because some of the fields that a new <code>LineModel</code> would require are not filled in.</p>
  
  <p>How can I get around this and allow updating the header and adding lines in one view?</p>