xml Document not called propertychanged

Question

Hello there I am new to xml and this is my first project working on xml files so needs bit help of yours
Data Layer
[global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_InputDataXML", DbType="Xml", UpdateCheck=UpdateCheck.Never)]
  public System.Xml.Linq.XDocument InputDataXML
  {
   get
   {
    return this._InputDataXML;
   }
   set
   {
    if ((this._InputDataXML != value))
    {
     this.OnInputDataXMLChanging(value);
     this.SendPropertyChanging();
     this._InputDataXML = value;
     this.SendPropertyChanged("InputDataXML");
     this.OnInputDataXMLChanged();
    }
   }
  }

MV
private XDocument _xmlDoc;
private StudyConfig _studyConfigData;
private XElement _parent;
private XElement _xElement;
void SetStudyConfigData ()
        {
            try
            {
                _studyConfigData = (from sc in _studyDataContext.StudyConfigs
                                    where sc.SiteId == SiteId && sc.StudyId == StudyId
                                    select sc).Single<StudyConfig>();
            }
            catch (Exception ex)
            {
            }
            finally
            {
                if (_studyConfigData == null)
                {
                    _studyConfigData = new StudyConfig();
                    _xmlDoc = new XDocument();
                    _parent = new XElement("Parent");
                    _xmlDoc.Add(_parent);
                    _dataExists = false;
                    _studyConfigData.InputDataXML = _xmlDoc;
                }
                else
                {
                    _xmlDoc = _studyConfigData.InputDataXML;
                    _dataExists = true;
                    _studyConfigData.InputDataXML = null;
                   // _studyDataContext.ExecuteCommand("UPDATE StudyConfig SET inputDataXML = NULL WHERE Id =" + _studyConfigData.Id);

                }
            }
                              
        }

public void AddElement(XElement Element)
        {
            SetStudyConfigData();
            _xmlDoc.Element("Parent").Add(Element);
            _studyConfigData.InputDataXML = _xmlDoc;
                // _parent.Add(Element);
           
           // _xmlDoc.Add(Element);
        }

At this point _xmlDoc =’ <Parent>
  <sample_Recieved number_of_itme="Int" date="DateTime" />
</Parent>’
And Element = ‘<sample_Recieved_Second number_of_itme="Int" date="DateTime" />’
So at the end of the function  _xmlDoc =
’ <Parent>
  <sample_Recieved number_of_itme="Int" date="DateTime" />
   <sample_Recieved_Second number_of_itme="Int" date="DateTime" />
</Parent>’
Its all looks good

public void Save()
        {
            try
             {
              
                if (!_dataExists)
                {
                   _studyDataContext.StudyConfigs.InsertOnSubmit(_studyConfigData);
                }
              
                _studyDataContext.SubmitChanges();
            }
            catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
        }

When I call save(); the change is not effecting the database
Any help would be appreciated