title: Entity Framework Core does not save related data
body: <p>In continuation of yesterday's <a href="https://stackoverflow.com/questions/40364084/ef-core-cannot-insert-the-value-null-into-column-with-default-value">post</a></p>
  
  <p>Two Entities</p>
  
  <pre><code>public class Realtor
  {
      public Realtor()
      {
          Guid = Guid.NewGuid();
          Registration = DateTime.Now;
      }
      public int Id { get; set; }
      public Guid Guid { get; set; }
      public string FirstName { get; set; }
      public string LastName { get; set; }
      public DateTime Registration { get; set; }
      public int SubdivId { get; set; }
      public Subdiv Subdiv { get; set; }
  }
  
  public class Subdiv
  {
      public Subdiv()
      {
          Created = DateTime.Now;
      }
      public int Id { get; set; }
      public string Name { get; set; }
      public DateTime Created { get; set; }
      public List&lt;Realtor&gt; Realtors { get; set; }
  }
  </code></pre>
  
  <p>I spend test</p>
  
  <ol>
  <li>I added one Subdiv (TOSTER TM) and received his ID</li>
  <li><p>Next, I add a Realtor and I push Subdiv property found on the ID, the newly created TOSTER TM
  Realtor.Subdiv is an object of type Subdiv. OK. 
  <a href="https://i.stack.imgur.com/v52UG.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/v52UG.jpg" alt="enter image description here"></a></p></li>
  <li><p>Then I try to select from the base the newly added Realtor.
  <code>Realtor.Subdiv = null</code> OMG!! 
  <a href="https://i.stack.imgur.com/8c0P0.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8c0P0.jpg" alt="enter image description here"></a></p></li>
  <li><p>We get Subdiv object, which is lacking in Realtor above and see his <code>List&lt;Realtor&gt; = null</code></p></li>
  </ol>
  
  <p><a href="https://i.stack.imgur.com/E41Bc.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/E41Bc.jpg" alt="enter image description here"></a></p>
  
  <p>Please help in solving this problem.</p>