MVC validation question

Hello all,

I have the following in my model a class:

  public class PatientSearchModel
    {
        //Patient Info
        public string MemberId { get; set; }
        public string PatientLastName { get; set; }
        public string PatientFirstName { get; set; }
        public string PatientDob { get; set; }
    }

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I need to add validation that the user has to have either MemberId OR Last, First and Dob.  How can I add the attributes for this check.  Not sure if I use ValidationMessageFor after this as well.

Thanks for any help.