title: Adding new related entities in a single action
body: <p>Every riddle has one or more questions, how can add both a Riddle and a Question to that riddle by submitting a single form?</p>
  
  <p>This is RiddlesController Create action code:</p>
  
  <pre><code>public ActionResult Create(RiddleViewModel model)
          {
              if (ModelState.IsValid)
              {
                  try
                  {
                      _db.Riddles.Add(new Models.Riddle
                      {
                          Name = model.Name,
                          Description = model.Description ,
                          CreationDate = DateTime.Now,
                          User = _db.Users.Find(User.Identity.GetUserId()),
                      });
                      _db.Questions.Add(new Models.Question
                      {
                          Body = model.FirstQuestionBody,
                          Answer = model.FirstQuestionAnswer,
                          CreationDate = DateTime.Now,
                          // What should I write here? or is there any better way to accomplish this?
                          Riddle = ????? 
                      });
                      _db.SaveChanges();
                      return RedirectToAction("Index");
                  }
  
                  catch
                  {
                      return View();
                  }
              }
              return View();
          }
  </code></pre>
  
  <p>This is Riddle model code:</p>
  
  <pre><code>public class Riddle
  {
      public int Id { get; set; }
      public string Name { get; set; }
      [MaxLength(200)]
      [DataType(DataType.MultilineText)]
      public string Description { get; set; }
      public List&lt;Review&gt; Reviews { get; set; }
      [Required]
      public ApplicationUser User { get; set; }
      public virtual List&lt;Question&gt; Questions { get; set; }
      [Column(TypeName = "datetime2")]
      public DateTime CreationDate { get; set; }    
  
  }
  </code></pre>
  
  <p>This is Question model code: </p>
  
  <pre><code> public class Question
      {
          public int Id { get; set; }
          public string Body { get; set; }
          public string Answer { get; set; }
          public Riddle Riddle { get; set; }
          [Column(TypeName ="datetime2")]
          public DateTime CreationDate { get; set; }
      }
  </code></pre>
  
  <p>This is RiddleViewModel code:</p>
  
  <pre><code>public class RiddleViewModel
      {
          [Required]
          public string Name { get; set; }
          [MaxLength(200)]
          [DataType(DataType.MultilineText)]
          public string Description { get; set; }
          // Question properties
          [DataType(DataType.MultilineText)]
          public string FirstQuestionBody { get; set; }
          public string FirstQuestionAnswer { get; set; }
      }
  </code></pre>