partial method implementation

namespace ePhoneBookMvc4Application.Models
{
    public partial class PhoneBook : ePhoneBookMvc4Application.Repositories.PhoneBook
    {


        public bool IsValid
        {
            get { return (GetRuleViolations().Count() == 0); }
        }


        public IEnumerable<RuleViolation> GetRuleViolations()
        {
            if (String.IsNullOrEmpty(FirstName))
            {
                yield return new RuleViolation("First Name Required", "FirstName");
            }

            if (!OnValidatePropertyForPhonebook.CharStringValidator(FirstName))
            {
                yield return new RuleViolation("Please Enter Valid First Name", "FirstName");
            }

            yield break;
        }

        
        partial void OnValidate(System.Data.Linq.ChangeAction action)
        {
            if(!IsValid)
            {
                throw new ApplicationException("Rule violations prevent saving");
            }
        }

    }
}

No defining declaration found for implementing declaration of partial method ePhoneBookMvc4Application.Models.PhoneBook.OnValidate(System.Data.Linq.ChangeAction)