title: API post to more than one table
body: <p>I have a API that gets messages saved in a database.</p>
  <p>The below controller GETs the message subjects which contain the message chains (two separate tables in my db), I have tested my get requested and works.</p>
  <p>I now need to create a POST request, but I'm not sure how to I can send the message subject info and the message chain info in one request, is this possible?</p>
  <p>Message Subject contains:</p>
  <pre><code>        [Key]
      public int MessageSubjectId { get; set; }
      public int UserId { get; set; }
      public string Subject { get; set; }
      public int OrderNumber { get; set; }
      public DateTime DateTime { get; set; }
      public Order Order { get; set; }
      public ICollection&lt;Message_Chain&gt; Message_Chain { get; set; }
  </code></pre>
  <p>Message Chain contains:</p>
  <pre><code> [Key]
      public int MessageChainId { get; set; }
      public int MessageSubjectId { get; set; }
      public string MessageBody { get; set; }
      public int SentFromId { get; set; }
      public DateTime DateTime { get; set; }
      public Message_Subject Message_Subject { get; set; }
  </code></pre>
  <p>My GET method:</p>
  <pre><code>   public async Task&lt;ActionResult&lt;IList&lt;Message_Subject&gt;&gt; GetOrderMessagesAsync(int orderNumber)
  {
   return await _context.Message_Subject
                     .Where(a =&gt; a.orderNumber== orderNumber)
                     .Include(m =&gt; m.Message_Chain)
                     .ToListAsync();
    
  }
  </code></pre>