ASP.NET MVC why does model validation ( Validator.TryValidateObject ) contain default ErrorMessages and not our own?

Question

ASP.NET

asp.net mvc 5 application.
global.asax defines custom adapter for RequiredAttribute

DataAnnotationsModelValidatorProvider.RegisterAdapter(typeof(RequiredAttribute), typeof(CustomRequiredAttributeAdapter));

CustomRequiredAttributeAdapter:

public CustomRequiredAttributeAdapter(ModelMetadata metadata, ControllerContext context, RequiredAttribute attribute)
            : base(metadata, context, attribute)
        {
            if (string.IsNullOrEmpty(attribute.ErrorMessage))
            {
                attribute.ErrorMessageResourceType = typeof(ValidationResources);
                attribute.ErrorMessageResourceName = "RequiredAttribute_ValidationError";
            }
        }

There is App_GlobalResources/ValidationResources.resx which defines its own ErrorMessages for the validator: The

controller method is called, in which the model is checked for validity -
...

var isValid = Validator.TryValidateObject(instance, validationContext, validationResults, true);

...
But the results of the check contain the default texts of the framework!

Wherein! If we run the same controller method again and again, already in this case, the result of the model check will be our own error texts (as it should be).

Why does this happen in 1 call?
Thanks

Answer 1

Only one of them should be set - either ErrorMessageString or ErrorMessageResourceName - but not both. Try explicitly setting ErrorMessage to null. Something like this:

[Required(ErrorMessage = null, ErrorMessageResourceName = “RequiredAttribute_ValidationError”, ErrorMessageResourceType = typeof(ValidationResources))]