ASP.NET MVC - DataAnnotation Localization

Strangely enough - especially seeing that localization has been a requirement in all of my work related codebases for the last 4 years or so, this is the first time that I am writing on the subject of localization.

In this post we're going to have a look at localizing DataAnnotations.

Observe the following data annotated snippet.

public class User
{
	[Display(Name = "FirstName")]
	public string FirstName { get; set; }

	[Display(Name = "LastName")]
	public string LastName { get; set; }

	[EmailAddress]
	[Required]
	[Display(Name = "Email")]
	public string Email { get; set; }
}

On the frontend (assuming you're using Razor), you will generally do something like this.

@Html.LabelFor(model => model.FirstName)
@Html.DisplayFor(model => model.FirstName)

In a nutshell, the LabelFor helper will output the display value associated with the property while the DisplayFor helper will output the most appropriate editor template it can find, e.g. date picker for a DateTime, checkbox for a bool etc.

The nice thing with this approach is that we've got a central point governing the output (and thereby input - validation) of our properties (perhaps too tightly coupled for MVC?).

Now in order to localize these properties, we need to add resx files to our solution, in the sample git repository linked with this post, I added resx files for Afrikaans and English, seen over here.

Note the use of Access Modifier: Public - this is required in order to make the resources visible to our models, quite strange that this isn't the default modifier, don't you think?

public class User
{
    [Display(Name = "FirstName", ResourceType = typeof(Resources.User))]
    public string FirstName { get; set; }

    [Display(Name = "LastName", ResourceType = typeof(Resources.User))]
    public string LastName { get; set; }

    [EmailAddress(ErrorMessageResourceName = "Email_InValid", ErrorMessageResourceType = typeof(Resources.User))]
    [Required(ErrorMessageResourceName = "Email_Required", ErrorMessageResourceType = typeof(Resources.User))]
    [Display(Name = "Email", ResourceType = typeof(Resources.User))]
    public string Email { get; set; }
}

public class MvcApplication : System.Web.HttpApplication
{
    protected void Application_Start()
    {
        ModelMetadataProviders.Current = new ResourceTypeModelMetadataProvider();

[ResourceType(typeof(Resources.User))]
public class User
{
    [Display(Name = "FirstName")]
    public string FirstName { get; set; }

    [Display(Name = "LastName")]
    public string LastName { get; set; }

    [EmailAddress(ErrorMessageResourceName = "Email_InValid")]
    [Required(ErrorMessageResourceName = "Email_Required")]
    [Display(Name = "Email")]
    public string Email { get; set; }
}

Instead of assigning a resourcetype to every property, we simply decorate the parent class.

But wait, there is more

You will notice that the DisplayAttribute is present in all of our snippets - its use is fairly repetitive, what if we could automate its inclusion into our code?

Enter PostSharp, instead of manually adding meta data, e.g. the display data annotation (among other things) to our code, its possible to bake these attributes into our classes compile time using the TypeLevelAspect - have a look at the ResourceTypeAttribute over here in Sample 3.

The amended snippet looks something like this.

[ResourceType(typeof(Resources.User))]
public class User
{
    public string FirstName { get; set; }

    public string LastName { get; set; }

    [EmailAddress(ErrorMessageResourceName = "Email_InValid")]
    [Required(ErrorMessageResourceName = "Email_Required")]
    public string Email { get; set; }
}

Not bad?

Note that these features are only included in the postsharp pay-for versions.