Uppercase attribute that converts the input to uppercase

Question

I am working in MVC4 and want to define a model using an Uppercase attribute. The idea would be that the presence of the Uppercase attribute would cause the model value to be converted to uppercase when it arrived at the server.

At the moment I have the following code within the model:

    [Required]
    [Display(Name="Account Code")]
    [StringValidation(RegExValidation.AccountCode, Uppercase=true)]
    public string Account
    {
        get { return _account; }
        set
        {
            if (value != null)
                _account = value.ToUpper();
        }
    }

But what I would really like is this:

    [Required]
    [Display(Name="Account Code")]
    [StringValidation(RegExValidation.AccountCode)]
    [Uppercase]
    public string Account { get; set; }

I think that I may need to create the Uppercase attribute as a ValidationAttribute to ensure it gets fired when the model hits the server. But that seems a bit wrong, as I'm not really validating the data. Is there a better way?

Also, is there any way to ensure the invocation order on the attributes? I really want to convert the data to uppercase before the custom StringValidation attribute fires, as this checks the case of the text in the regex pattern.

To add a bit of background to this, I want to reduce the need to add code to uppercase the data. The nirvana would be a single attribute, which updates the data on the way into the server, either in the model binding or validation stage. This attribute can then be referenced in the StringValidation attribute to amend the RegEx value used in its checks. I can also then lookup this attribute in a custom TextBoxFor helper method, such that I can add text-transform: uppercase so it looks correct on the client side.

Does anyone have any ideas out there?

Answer 1

I have managed to get this working, to a point, so here's my solution for others to appraise.

Once point to note was that the full solution couldn't be achieved because I couldn't get the Modelmetadata inside the StringValidation.IsValid() attribute. The particular issue I had here was that I could get the Metadata, however I could not get the PropertyName from it, only the DisplayName. There were multiple options out there, but the fact that some of my properties have the same DisplayName means that I couldn't be sure that the ProprtyName was the one I was actually validating.

Here's the code for the ValidationAttribute:

public class StringValidationAttribute : ValidationAttribute, IClientValidatable, IMetadataAware {

    private bool _uppercase;

    public StringValidationAttribute(bool uppercase = false) {
         _uppercase = uppercase;
    }

    ...

    public void OnMetadataCreated(ModelMetadata metadata)
    {
        metadata.AdditionalValues["Uppercase"] = _uppercase;
    }
}

I then created a new IModelBinder implementation:

public class StringBinder : IModelBinder
{
    public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {           
        ValueProviderResult result = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);

        if (result == null)
            return null;

        if (bindingContext.ModelMetadata.AdditionalValues.ContainsKey("Uppercase")) {
            if ((bool)bindingContext.ModelMetadata.AdditionalValues["Uppercase"]])
                return result.AttemptedValue.ToUpper();
        }

        return result.AttemptedValue;
    }
}

And registered that in myGlobal.asax file:

ModelBinders.Binders.Add(typeof(string), new StringBinder());

The code so far will cause any string input coming into MVC to be converted to Uppercase if it has StringValidationAttribute attached to it on the model, and where the uppercase indicator has been set.

Next, to achieve my desire of making the html forms be uppercase too, I implemented a new EditorTemplate named string.cshtml. In this view I added:

RouteValueDictionary htmlAttributes = new RouteValueDictionary();
if ((bool)ViewData.ModelMetadata.AdditionalValues["Uppercase"]) {
    htmlAttributes.Add("class", "Uppercase");
}
@Html.TextBox("", Model, htmlAttributes)

With the CSS as;

.Uppercase {
    text-transform: uppercase;
}

Hope this post helps some others out there.

Answer 2

For Web API purpose it is better to convert the incoming json to uppercase or lowercase.

    public class ToUpperCase : JsonConverter
    {
        public override bool CanConvert(Type objectType)
        {
            return objectType == typeof(string);
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            return reader.Value.ToString().ToUpper();
        }            
    }



    [Display(Name = "PNR NAME")]
    [JsonConverter(typeof(Annotations.ToUpperCase))]
    public string PNR { get; set; }

OR Globally;

  protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();
        //.......... others



        JsonMediaTypeFormatter jsonFormatter = GlobalConfiguration.Configuration.Formatters.JsonFormatter;
        JsonSerializerSettings jSettings = new Newtonsoft.Json.JsonSerializerSettings();
        jSettings.Converters.Add(new UpperCaseStringConverter());
        jsonFormatter.SerializerSettings = jSettings;
    }

Answer 3

You're right, ValidationAttribute is not the right fit. It seems like doing this at the Model Binding stage would be a better idea. See this article for a detailed explanation of how to customize this behavior.

Based on the information provided there, I believe you should be able to create an attribute based on CustomModelBinderAttribute like this:

[AttributeUsage(AttributeTargets.Property)]
public class UppercaseAttribute : CustomModelBinderAttribute
{
    public override IModelBinder GetBinder()
    {
        return new UppercaseModelBinder();
    }

    private class UppercaseModelBinder : DefaultModelBinder
    {
        public override object BindModel(
            ControllerContext controllerContext,
            ModelBindingContext bindingContext)
        {
            var value = base.BindModel(controllerContext, bindingContext);
            var strValue = value as string;
            if (strValue == null)
                return value;
            return strValue.ToUpperInvariant();
        }
    }
}

I have not tested this. Let me know if it works or not.

Answer 4

NOTE: I'm adding on to this post because until I discovered the approach I now use, I read this and tried all above unsuccessfully.

I generally use a two part process when dealing with forcing text data to be formatted as uppercase. 1. at the view and 2. at the controller

1. At the view layer so that the user knows data is going to be used in the uppercase form. This can be down through htmlAttributes used in the EditorFor HTML helper.

   @HTML.EditorFor(model => model.Access_Code, new { htmlAttributes = new  Style= "text-transform:uppercase"}})
   

Now this only forces the data seen and entered by the user to uppercase and not the data sent to the server. To do that requires some code in the associated method in the controller.

2. I add the ToUpper() method to the target attribute of the object being passed back to the contoller. Here is hypothetical example showing this.

   public ActionResult verify(int? id)
         {
           var userData = db.user.Where (i=> i.userID == id).Single();
   
           userData.Access_Code = userData.Access_Code.ToUpper();
   
      ...
    }