#1) I've till now, seen absolutely 0 examples of how to handle any sort of validation, and would like to see anythign that would help out there. #2) Can server controls be used?

Excellent remark! I am also looking for something for validating my forms with the MVC Framework. Can someone help? 

ronnyek:

Can server controls be used?

 

If you meant the validation controls, they cannot be used (yet?) because they validate other server controls, which in turn require a form with runat=server.

It's possible and probable that the MVC team will provide validation helpers (or even the MVC cotrib project) for client-side validation. The other half of the story is the server-side validation, which will be split into model code that validates the fields and controller code that reports validation problems to the user. See the following fictitious code:

 

[ControllerAction]
public void Create()
{
  Product prod = new Product();
  prod.UpdateFrom(Request.Form);

  ValidationResult result;
  result = product.Validate();
  if(result.Success)
  {
     ProductRepository.Save(prod);
     RedirectToAction("List");
  }
  else //validation failed
  {
    TempData["validationErrors"] = result.GetErrorMessages();
    RedirectToAction("New");  
  }
}

  

http://haacked.com/archive/2007/12/21/asp.net-mvc-helpers-for-repopulating-a-form.aspx

 Look at jquery validate... Its the best client side validation framework I have found thus far.  As we work on Client Script support for Mvc Contrib I am hoping to include validation in some way to make it easier.

 @ Sergio Pereira:

How can I use ValidationResult ?

(I use LINQ).

It would be great if you could provide another fictitious code.

Thank you. 

OK. More fictitious code to the rescue.

  

public partial class Product
{
  public ValidationResult Validate()
  {
     ValidationResult result = new ValidationResult();

     if(this.Name.IndexOfAny('~', '!', '^'))
     {
        result.AddError("The product Name has invalid characters.");
     }

     if(this.UnitPrice < 0.0)
     {
        result.AddError("The product price cannot be negative.");
     }

     //..and so on...

     return result;
  }
}

public class ValidationResult
{
  public ValidationResult() {  }

  private List<string> messages = new List<string>();
  public bool Success {get{ return messages.Count > 0;} }

  public void AddError(string errorMsg)
  {
    messages.Add(errorMsg);
  }
  
  public string[] GetErrorMessages()
  {
    return messages.ToArray();
  }
}

 

Needless to say, this is not tested and based on more complex real code. 

@ Sergio Pereira:

Thanks! It looks great!

However, there is a little something I quite don't understand.

Is there something in common between your class ValidationResult and this one:

http://msdn2.microsoft.com/en-us/library/system.windows.controls.validationresult.aspx

?
 

dimi3:

Is there something in common between your class ValidationResult and this one:

http://msdn2.microsoft.com/en-us/library/system.windows.controls.validationresult.aspx

Yes, the name :) The class you mention appears to be part of WPF.

Ok :)

Thank you for your answers.

(I personally consider this post as Resolved)

I wish you a happy new year.
 

I have some other questions...

How should I modify the code above if I want to "save" an error for a specific field (for example, the email address) in order to place this specific error besides the Textbox ?  

Simply change AddError(string errorMsg) to AddError(string errorMsg, string property)

and instead of storing a List<string> store a Dictionary<string, string>

that way you can associate the error message with the html element and display the message next to it. 

Thank you tgmdbm for you answer!

I modified the class from Sergio Pereira as follow:

 

1    public class ValidationResult
2        {
3            public ValidationResult() { }
4    
5            private Dictionary<String, String> messages = new Dictionary<String, String>();
6            public bool Success { get { return messages.Count == 0; } }
7    
8            public void AddError(String field, String errorMessage)
9            {
10               messages.Add(field, errorMessage);
11           }
12   
13           public Dictionary<String, String> GetErrorMessages()
14           {
15               return messages;
16           }
17       }

Then in the controller, I have:

1    TempData["validationErrors"] = validationResult.GetErrorMessages();

TempData["validationErrors"] is now a Dictionary<String, String>

How can I access each element in the .aspx view?

(ViewContext.TempData.SafeGet("validationErrors") is a String)
  

 

dimi3:

TempData["validationErrors"] is now a Dictionary<String, String>
How can I access each element in the .aspx view?

 

The same way you would iterate any other dictionary:

<b>Errors:</b><br />
<ul class="errors">
<% foreach(string field in ((IDictionary<string,string>)TempData["validationErrors"]).Keys ) { %>
   <li><i><%= field %></i>: <%= ((IDictionary<string,string>)TempData["validationErrors"])[field] %></li>
<% } %>
</ul>

This looks pretty ugly. If I were you I'd create some user control that takes care of this code and put it in the master page, if you have one.

I'd have to call bug on this.

SafeGet should return an object, perhaps a SafeGetString to attempt a ToString() on the object?

it should be as easy as you think

<%= Html.TextBox( "fieldName", ViewData.FieldName ) %> <%= ViewContext.TempData.SafeGet("errors")["FieldName"] %>

But you can always (and probably should) write an extension method to do this.

public static string Error(this HtmlHelper helper, string fieldName) {
  string s = string.Empty;

  ViewContext.TempData.SafeGet("errors").TryGetValue(fieldName, s);

  return s;

}

then it's just 

<%= Html.TextBox( "fieldName", ViewData.FieldName ) %> <%= Html.Error("FieldName") %>