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 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(
        this ModelStateDictionary modelState, 
        Expression> ex, 
        string message
    )
    {
        var key = ExpressionHelper.GetExpressionText(ex);
        modelState.AddModelError(key, message);
    }
}

and then use this method:

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