title: Foreign key not updated (configured with required principal-dependent)
body: <p>Fluent API config:</p>
  
  <pre><code>internal class UserMap : EntityTypeConfiguration&lt;User&gt;
      {
          public UserMap()
          {
              Property(x =&gt; x.CSL).IsRequired();
  
              //relational properties
              HasRequired(x =&gt; x.UserType).WithMany(x =&gt; x.Users).HasForeignKey(x =&gt; x.UserType_ID).WillCascadeOnDelete(true);
              HasRequired(x =&gt; x.TimelineVolumetry).WithRequiredPrincipal(x =&gt; x.User).WillCascadeOnDelete(true);           
          }
      }
  
  internal class TimelineVolumetryMap : EntityTypeConfiguration&lt;TimelineVolumetry&gt;
      {
          public TimelineVolumetryMap()
          {
              Property(x =&gt; x.AllowedWeeks).IsRequired();
  
              //relational properties
              HasRequired(x =&gt; x.User).WithRequiredDependent(x =&gt; x.TimelineVolumetry).WillCascadeOnDelete(true);
          }
      }
  </code></pre>
  
  <p>Insert query:</p>
  
  <pre><code>User u = new User();
  u.CSL = csl;
  u.UserType_ID = role;
  u.TimelineVolumetry = new TimelineVolumetry();
  u.TimelineVolumetry.User = u;
  ctx.User.Add(u);
  ctx.SaveChanges();
  </code></pre>
  
  <p>After inserting a user in the database I get <code>User_ID = 0</code> for <code>TimelineVolumetry</code>. Is there a way to auto set the <code>User_ID</code> when adding a user or am I forced to save the <code>TimelineVolumetry</code> again after setting the foreign key?</p>
  
  <pre><code>public class TimelineVolumetry
      {
          public int ID { get; set; }
          public int AllowedWeeks { get; set; }
  
          //relational properties
          public int User_ID { get; set; }
          public User User { get; set; }
  
          public TimelineVolumetry()
          {
              AllowedWeeks = 0;
          }
      }
  </code></pre>