title: MVC model validation depending on whether form is populated or not
body: <p>I have a viewmodel which consists of three models which are all displayed on the screen as one single form.</p>
  
  <pre><code>public class ViewModel
  {
      public PersonVM person { get; set; }
      public DepartmentVM department { get; set; }
      public EmploymentVM employment { get; set; }
  }
  </code></pre>
  
  <p>When users fill in the form, they can fill one model details (example:- Person) and leave the other models details empty.</p>
  
  <p>How do I implement model validation in my action method for all three models. I want to do model validation only if the model is populated (not null) for each of them.</p>
  
  <p>How do I implement model validation depending on whether the individual model is populated or not ?</p>