Question

My question is regarding MVC 2 custom validation. I’m stuck on a particular issue and I’m unsure how to get around it. I’m fairly sure it’s more figuring out how to do it logically and then implementing it in code.

So what we have is a metadata class for a product. Each product has a product product ID which is the PK, and obviously unique. Each product also has a product code which is also unique. Customers enter the product code however, but the nature of the code ensures that only one code is attached to one product so it will be unique.

Here is a snippet from the metadata class:

 public partial class ProductMetadata
    {
        [DisplayName("Product Name")]
        [Required(ErrorMessage = "Product Name is required.")]
        public string ProductName { get; set; }

        [DisplayName("Product Code")]
        [Required(ErrorMessage = "Product Code is required.")]
        [ProductCodeAlreadyExistsValidator(ErrorMessage = "This Product code is in use.")]        
        public string ProductCode { get; set; }
}

The ‘ProductCodeAlreadyExistsValidator’ works perfectly when creating a new product. The problem lies in editing an existing product as the validation is being performed on this attribute again, and it is finding itself in the database. This results in the validation failing.

Here is a snippet from the custom validator:

public class ProductCodeAlreadyExistsValidator : ValidationAttribute
    {
        private readonly object typeId = new object();
        private const string defaultErrorMessage = "Product Code {0} is already present in the system.";

        public ProductCodeAlreadyExistsValidator()
            : base(defaultErrorMessage)
        {
        }

        public override object TypeId
        {
            get
            {
                return typeId;
            }
        }

        public string CustomerType { get; set; }
        public string CustomerFriendlyType { get; set; }

        public override string FormatErrorMessage(string roleName)
        {
            return String.Format(CultureInfo.CurrentUICulture, ErrorMessageString, roleName);
        }

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            if (!IsValid(value))
            {
                string errorMessage = string.Format(defaultErrorMessage, validationContext.MemberName, value as string);
                return new ValidationResult(errorMessage, new string[] { validationContext.MemberName });
            }

            return null;
        }

        public override bool IsValid(object value)
        {
            bool alreadyPresent = false;

            string ProductCode = value as string;

            using (ModelContainer ctn = new ModelContainer())
            {
                alreadyPresent = ctn.Products.Where(t => t.ProductCode == ProductCode).Count() > 0;
            }

            return !alreadyPresent;
        }
    }

It might be a relatively simple fix however I seem to have hit a brick wall with it. Can anyone offer any advice?

Answer 1

Code seems ok to me. I think you need to identify if you are doing an insert or an update so the validation can ignore the checking when updating the field. You could check if the ID of the item editted is the same ID found by the code, it would be identified as a Editting.