String join in Linq

var userInfo = (from user in user)
                           select new userModel
                           {
                               UserID = user.UserID,
                               FirstName = ud.AC_tbl_String_FirstName == null ? "" : ud.AC_tbl_String_FirstName.Value,
                               LastName = ud.AC_tbl_String_LastName == null ? "" : ud.AC_tbl_String_LastName.Value,
          ).ToList(),
                               HobbylList = entity.tbl_Hobbies.Where(k => k.UserID == user.UserID).Select(k => k.Name).Distinct().ToList()
                           }).FirstOrDefault();
         
         

  public class userModel
    {      
        public string hobbies
        {
            get
            {
                return string.Join(",", HobbylList); 
            }
        }

        public List<string> HobbylList { get; set; }
}