Custom validation attribute's set error message not showing as predicted

Question

I have a custom validation attribute:

public class RequireIfPropertyIsFalseAttribute : ValidationAttribute
    {
        private string basisProperty { get; set; }
        public RequireIfPropertyIsFalseAttribute(string basisProperty)
        {
            this.basisProperty = basisProperty;
        }

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            var basisProp = validationContext.ObjectType.GetProperty(basisProperty);
            var isFalse = !(bool)basisProp.GetValue(validationContext.ObjectInstance, null);

            if (isFalse)
            {
                if (value == null || (value.GetType() == typeof(string) && string.IsNullOrEmpty(((string)value).Trim())))
                        return new ValidationResult(this.ErrorMessage);
            }

            return ValidationResult.Success;
        }
    }

I use it for both Model properties:

public bool NoAgeProvided { get; set; }
[RequireIfPropertyIsFalse(nameof(NoAgeProvided), ErrorMessage = "This is required")]
[Display(Name = "Age")]
public int Age { get; set; }

public bool NoNameProvided { get; set; }
[RequireIfPropertyIsFalse(nameof(NoNameProvided), ErrorMessage = "This is required")]
[Display(Name = "Name")]
public string Name { get; set; }

Upon validation, the Name validation message shows "This is required". However, for the Age property, "The Age field is required" is displaying on the validation message. What am I doing wrong? How can I display the set ErrorMessage?

user3559349 · Accepted Answer · 2017-09-19 02:04:11Z

1

Because property Age is typeof int, it is always required (an int cannot be null) and if you leave the textbox empty, a null value is submitted and the Required validation is executed first and that error message is displayed.

Change you property to be nullable

public int? Age { get; set; }

Note that it works for your Name property because its string which is nullable by default.

As a side note, you should consider implementing IClientValidatable so that you can get client side validation as well. Refer The Complete Guide To Validation In ASP.NET MVC 3 - Part 2.

answered Sep 19, 2017 at 2:04

user3559349

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4 Comments

Kristianne Nerona Over a year ago

I suspected that that is the case. However, making the field nullable would also mean I have to change the associated database table column's is null attribute. I'll read the link that you provided. Thank you so much!

user3559349 Over a year ago

Your editing data so you ALWAYS use a view model, not data models in a view.

user3559349 Over a year ago

In any case, what would you expect to store in that db column if its not provided (a value of 0 would not make sense)

Kristianne Nerona Over a year ago

Tbh the client's requirements are murky right now, I have a non nullable table column and a nullable model property. I was hoping I could find a way to make the validation for the contrasting nature of the two fields. The requirements may change in the future, but for now I am working for a solution. I am still reading the link that you provided, thanks!

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