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I was building a form that had two fields: home phone number and mobile phone number.

The client needed at least one of the two fields filled out.

Given the existing DataAnnotations nothing fit the bill in this case. I ended up creating a custom validation attribute that is applied at the class level.

I based it off of the PropertiesMustMatchAttribute custom attribute that is included in the AccountModels.cs/vb file within the default ASP.NET MVC 2 application project template (just do a File->New ASP.NET MVC 2 Web Project within VS 2010 and look for this class).

First off in the ContactModel.cs I added:

using System.ComponentModel.DataAnnotations;
using System.Globalization;

[AttributeUsage(AttributeTargets.Class, AllowMultiple = true, Inherited = true)]
    public sealed class OneOrOtherFieldRequired : ValidationAttribute
    {
        private const string _defaultErrorMessage = "'{0}' or '{1}' are required.";
        private readonly object _typeId = new object();

        public OneOrOtherFieldRequired(string field1, string field2)
            : base(_defaultErrorMessage)
        {
            Field1 = field1;
            Field2 = field2;
        }

        public string Field1 { get; private set; }
        public string Field2 { get; private set; }

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

        public override string FormatErrorMessage(string name)
        {
            return String.Format(CultureInfo.CurrentUICulture, ErrorMessageString, Field1, Field2);
        }

        public override bool IsValid(object value)
        {
            PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(value);
            object field1 = properties.Find(Field1, true).GetValue(value);
            object field2 = properties.Find(Field2, true).GetValue(value);
            string valueAsString1 = field1 as string;
            string valueAsString2 = field2 as string;
            if (String.IsNullOrEmpty(valueAsString1) && String.IsNullOrEmpty(valueAsString2))
            {
                return false;
            }
            return true;
        }
    }

I then created in ContactModel.cs the ContactModel class.  In this class I have among other properties the two phone number properies: HomePhoneNumber and MobilePhoneNumber.

 [OneOrOtherFieldRequired("HomePhone", "MobilePhone", ErrorMessage="Please fill in either your home or mobile number.")]
    public class ContactModel
    {
       ...
        public String HomePhone { get; set; }
        public String MobilePhone { get; set; }

In the ContactController I have an action:

        [HttpPost]
        public ActionResult Index(Contact contact)
        {
            if (ModelState.IsValid)
            {
                contact.Store();
                contact.SendEmail();
                ViewData["ShowForm"] = false;
                return View();
            }
            ViewData["ShowForm"] = true;
            return View(contact);
        }

When creating the view make sure to create a strongly typed view on the ContactModel

In the View I add the validation summary to display the error message if the requirement isn’t fulfilled.

<%= Html.ValidationSummary(true, "Please correct invalid and required fields.") %>

Filed under: asp.net   Tags: MVC,
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