title: How to do server-side validation using MVC 5
body: <p>I am working on a simple auction website for a charity. I have an Item model for the sale items, and a Bid view where the user can enter a bid and submit it. This bid is received inside the Item controller:</p>
  
  <pre><code>    [HttpPost]
      [ValidateAntiForgeryToken]
      public ActionResult Bid(int itemID, int bidAmount)
      {
          if (ModelState.IsValid)
          {
              Item item = db.Items.Find(itemID);
              if (bidAmount &gt;= item.NextBid)
              {
                  item.Bids++;
                  item.CurrentBid = bidAmount;
                  item.HighBidder = HttpContext.User.Identity.Name;
                  db.Entry(item).State = EntityState.Modified;
                  db.SaveChanges();
              }
              else
              {
                  // Already outbid
              }
              return View(item);
          }
          return RedirectToAction("Auction");
      }
  </code></pre>
  
  <p>I would like to know how to display server-side validation to the user. For example, in the above code, it may be that the submitted bid amount is no longer sufficient. In that case, I would like to display a message to the user that they have been outbid etc.</p>
  
  <p>How can I pass this information back to the view to display an appropriate message? I want the user to see the same item page view as before, updating the value in the edit box and displaying the message - similar to eBay. Thanks.</p>