Get error message when using custom validation attribute

Question

I'm using the CustomValidationAttribute like this

[CustomValidation(typeof(MyValidator),"Validate",ErrorMessage = "Foo")]

And my validator contains this code

public class MyValidator {
    public static ValidationResult Validate(TestProperty testProperty, ValidationContext validationContext) {
        if (string.IsNullOrEmpty(testProperty.Name)) {
            return new ValidationResult(""); <-- how can I get the error message  from the custom validation attribute? 
        }
        return ValidationResult.Success;
    }
}

So how can I get the error message from the custom validation attribute?

score 8 · Answer 1 · edited Jun 30 '16 at 11:50

8

I know this is a little of an old post, but I will provide an better answer to the question.

The asker wants to use the CustomValidationAttribute and pass in an error message using the ErrorMessage property.

If you would like your static method to use the error message that you provided when decorating your property, then you return either:

new ValidationResult(string.Empty) or ValidationResult("") or ValidationResult(null).

The CustomValidationAttribute overrides the FormatErrorMessage of its base class and does a conditional check for string.IsNullOrEmpty.

edited Jun 30 '16 at 11:50

Jack Pettinger

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answered Oct 22 '14 at 14:43

Kirby

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1
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21

Thank you. Exactly what I was looking for. – MTR Feb 04 '16 at 09:50

score 7 · Accepted Answer · answered Sep 23 '12 at 13:39

There's no reliable way to get the error message from the attribute. Alternatively you could write a custom validation attribute:

[MyValidator(ErrorMessage = "Foo")]
public TestProperty SomeProperty { get; set; }

like this:

public class MyValidatorAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var testProperty = (TestProperty)value;
        if (testProperty == null || string.IsNullOrEmpty(testProperty.Name))
        {
            return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
        }

        return null;
    }
}

In this case the error message will be inferred from the custom validation attribute.

Yes there is a reliable way. For a better answer to the actual question asked please see my answer below. — Kirby, Oct 22 '14 at 14:43

score 0 · Answer 3 · edited May 23 '17 at 12:02

0

You can look into the following posting to get some ideas on how to do what you want to do (they use JS):

Custom validator error text through javascript?

Hope this helps.

edited May 23 '17 at 12:02

Community

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answered Sep 23 '12 at 13:37

Display Name

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score 0 · Answer 4 · answered Oct 10 '13 at 21:10

The only way I have found that works is to validate the model from the post back method using TryValidateObject and if it fails, show the model again - then the error will show up.

    [HttpPost]
    public ActionResult Standard(Standard model)
    {
        var valContext = new ValidationContext(model, null, null);
        var valResults = new List<ValidationResult>();;
        bool b = Validator.TryValidateObject(model, valContext, valResults, true);
        if(!b)
            return View(model);
        ...

Get error message when using custom validation attribute

4 Answers4

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