ValidationMessageFor together with AddModelError(key, message). What's the key?

Question

I am developing a client-side and server-side validation for a certain viewModel property.

In the .cshtml file I put this:

@Html.DropDow         


        

Answer 1

You want the validation to happen at both the client and server side and also you looking for an elegant solution then why can try creating a custom ValidationAttribute.

Answer 2

I follow @Darin Dimitrov solution but i want to avoid <MyViewModel, int> so I used some different way but for that you need MyViewModel object variable.

public static class ModelStateExtensions
{
    public static void AddModelError<TModel, TProperty>(this TModel source,        
                                                    Expression<Func<TModel, TProperty>> ex, 
                                                    string message,
                                                    ModelStateDictionary modelState)
    {
        var key = System.Web.Mvc.ExpressionHelper.GetExpressionText(ex);
        modelState.AddModelError(key, message);
    }
}

How to Use:

catch (BusinessException e)
{
    objMyViewModel.AddModelError(x => x.EntityType.ParentId, 
                                 Messages.CircularReference,
                                 ModelState);
}

Answer 3

You could write an extension method that will take a lambda expression for the key instead of a string:

public static class ModelStateExtensions
{
    public static void AddModelError<TModel, TProperty>(
        this ModelStateDictionary modelState, 
        Expression<Func<TModel, TProperty>> ex, 
        string message
    )
    {
        var key = ExpressionHelper.GetExpressionText(ex);
        modelState.AddModelError(key, message);
    }
}

and then use this method:

catch (BusinessException e)
{
    ModelState.AddModelError<MyViewModel, int>(
        x => x.EntityType.ParentId, 
        Messages.CircularReference
    );
}