linq, mvc and partial class

public partial class User
    {
        public string FullName
        {
            get
            {
                return FirstName + " " + LastName;
            }
        }
    }

<%=ViewData.Model.FullName %>

CS1061: 'PR.Web.Models.User' does not contain a definition for 'FullName' and no extension method 'FullName' accepting a first argument of type 'PR.Web.Models.User' could be found (are you missing a using directive or an assembly reference?)