Using conditional statements while validating using attributes in MVC?

Question

I am wondering if it is possible to use If statements when adding validation using attributes in MVC. Everything I have so far works out but there are certain values that are dependent on user input. For example:

Zip Validation:

If country is US, ensure ZIP is 5 digits long

If country is Canada, require data in “A1A 1A1” format

    public class Customer
{
    public int MasterContactID { get; set; }
    [Required(ErrorMessage="Please enter company")]
    public string Company { get; set; }
    [Required(ErrorMessage = "Please enter a contact name")]
    public string Contact { get; set; }
    [Required(ErrorMessage = "Please enter an address")]
    public string Address1 { get; set; }
    public string Address2 { get; set; }
    [Required(ErrorMessage = "Please enter a city")]
    public string City { get; set; }
    [Required(ErrorMessage = "Please enter State")]
    public string State { get; set; }
    [Required(ErrorMessage = "Please enter Country")]
    public string Country { get; set; }
    [Required(ErrorMessage = "Please enter Zip")]
    public string Zip { get; set; }
    public string Zip4 { get; set; }
    [Required(ErrorMessage = "Please enter an Email Address")]
    [EmailAddress(ErrorMessage = "Please enter a valid Email Address")]
    public string Email { get; set; }
    [RegularExpression(@"^\(?([0-9]{3})\)?[-. ]?([0-9]{3})[-. ]?([0-9]{4})$", ErrorMessage = "Please enter valid phone number (xxx-xxx-xxxx) ")]
    public string Phone { get; set; }
    [Required (ErrorMessage = "Please indicate whether ACTIVE or INACTIVE")]
    public string CustStatus { get; set; }
    public enum Status
    {
        ACTIVE,
        INACTIVE
    }
}

Apologies if this isn't the proper way to ask a question on here as this is the first question I ask. Thank you.

Answer 1

Solution 1: Custom ValidationAttribute

You can implement a custom ValidationAttribute that inherits ValidationAttribute.

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = true)]
public class ZipValidationAttribute : ValidationAttribute
{
    private readonly string _dependsOn;
    
    public ZipValidationAttribute(string dependsOn) : base()
    {
        _dependsOn = dependsOn;
    }
    
    public ZipValidationAttribute(string dependsOn, string errorMessage) : base(errorMessage)
    {
        _dependsOn = dependsOn;
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        ValidationResult validationResult = ValidationResult.Success;
    
        try
        {
            string input = (string)value;
        
            if (String.IsNullOrEmpty(input))
                return validationResult;
            
            // Using reflection to get a reference to the other property
            var countryPropertyInfo = validationContext.ObjectType.GetProperty(_dependsOn);
            string countryPropertyValue = (string)countryPropertyInfo.GetValue(validationContext.ObjectInstance, null);
            switch (countryPropertyValue)
            {
                case "US":
                    if (input.Length != 5)
                    {
                        validationResult = new ValidationResult("When select country: US, Zip must be with 5 characters.");
                    }
                    break;
                case "Canada":
                    Regex r = new Regex(@"^[a-zA-Z]\d[a-zA-Z]\s\d[a-zA-Z]\d$");
                    if (!r.IsMatch(input))
                    {
                        validationResult = new ValidationResult("When select country: Canada, Zip must be in 'A1A 1A1' format.");
                    }
                    break;
            }
        }
        catch (Exception ex)
        {
            throw ex;
        }

        return validationResult;
    }
}

And apply [ZipValidation("Country")] attribute to Zip property. Pass "Country" as the custom validation will be depended on the Country property.

public class Customer
{
    ...

    [Required(ErrorMessage = "Please enter Zip")]
    [ZipValidation("Country")]
    public string Zip { get; set; }
}

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Solution 2: Implement IValidatableObject.

Customer class to implement IValidatableObject

public class Customer : IValidatableObject
{

    ...

    [Required(ErrorMessage = "Please enter Country")]
    public string Country { get; set; }

    [Required(ErrorMessage = "Please enter Zip")]
    public string Zip { get; set; }
    
    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        var results = new List<ValidationResult>();
        switch (this.Country)
        {
            case "US":
                if (this.Zip.Length != 5)
                {
                    results.Add(new ValidationResult("When select country: US, Zip must be with 5 characters."));
                }
                break;
            case "Canada":
                Regex r = new Regex(@"^[a-zA-Z]\d[a-zA-Z]\s\d[a-zA-Z]\d$");
                if (!r.IsMatch(this.Zip))
                {
                    results.Add(new ValidationResult("When select country: Canada, Zip must be in 'A1A 1A1' format."));
                }
                break;
        }
            
        return results;
    }
}

Sample program (Solution 2)

---

Solution 3: Perform the validation in Controller

Implement the validation in the controller method. And when it fails the validation, pass the error message to ModelState.Errors and return to View.