problemDB

/* present in Insert.xaml.cs */
     private void button1_Click(object sender, RoutedEventArgs e)
        {         if (textBox1.Text.Length > 0)
          {
                DB.Interventi newInterventi = new DB.Interventi
                {
                  Element =textBox1.Text,
                  Note =textBox1.Text.Length,
                      //I use a listPicker for select element
                  Category = (DB.Elements)listPicker.SelectedItem
                };
                MessageBox.Show("data insert");
          }
            else
            {

               MessageBox.Show("Insert Element");
            }

           App.ViewModel.SaveDB(); }


/* class Elementi.cs */

     [Table]
    public class Elementi : INotifyPropertyChanged, INotifyPropertyChanging
    {

        // definisco ID degli elementi del'auto
        private int _id;

        [Column(DbType = "INT NOT NULL IDENTITY", IsDbGenerated = true, IsPrimaryKey = true)]
        public int Id
        {
            get { return _id; }
            set
            {
                NotifyPropertyChanging("Id");
                _id = value;
                NotifyPropertyChanged("Id");
            }
        }

        private string _elemento;
       [Column]
        public string Elemento
        {
            get { return _elemento; }
            set
            {
                NotifyPropertyChanging("Elemento");
                _elemento = value;
                NotifyPropertyChanged("Elemento");
            }
        }

        [Column(IsVersion = true)]
        private Binary _version;

        // Define the entity set for the collection side of the relationship.
        private EntitySet<Interventi> _allInterventi;


        // ASSOCIATION
        [Association(Storage = "_allInterventi", OtherKey = "_categoryId", ThisKey = "Id")]
        public EntitySet<Interventi> AllInterventi
        {
            get { return this._allInterventi; }
            set { this._allInterventi.Assign(value); }
        }

        public Elementi()
        {
            _allInterventi = new EntitySet<Interventi>(
                new Action<Interventi>(this.add_Intervento),
                new Action<Interventi>(this.remove_Intervento)
                );
        }

        // add
        private void add_Intervento(Interventi interv)
        {
            NotifyPropertyChanging("Interventi");
            interv.Category = this;
        }

        // remove
        private void remove_Intervento(Interventi interv)
        {
            NotifyPropertyChanging("Interventi");
            interv.Category = null;
        }



/* class Interventi.cs*/

          [Table]
    public class Interventi : INotifyPropertyChanged, INotifyPropertyChanging
    {
            private int _InterventoId;

    [Column(IsPrimaryKey = true, IsDbGenerated = true, DbType = "INT NOT NULL Identity", CanBeNull = false, AutoSync = AutoSync.OnInsert)]
            public int InterventoId
            {
                get { return _InterventoId; }
                set
                {

                    if (_InterventoId != value)
                        NotifyPropertyChanged("InterventoId");
                    this._InterventoId = value;
                    NotifyPropertyChanged("InterventoId");

                }

            }

    private string _Element;
    [Column(CanBeNull = false)]
    public string Element
    {
        get { return _Element; }

        set {
                if (_Kilometraggio != value)
                {
                    NotifyPropertyChanging("Element");
                    _Kilometraggio = value;
                    NotifyPropertyChanged("Element");
                }
    }
    }

    private string _Note;
    [Column(CanBeNull = true)]
    public string Note
    {
        get { return _Note; }

        set
        {
            if (_Note != value)
            {
                NotifyPropertyChanging("Note");
                _Note = value;
                NotifyPropertyChanged("Note");
            }
        }
    }

    [Column(IsVersion = true)]
    private Binary _version;
    [Column]
    internal int _categoryId;
    private EntityRef<Elementi> _category;
      //ASSOCIATION
        [Association(Storage = "_category", ThisKey = "_categoryId", OtherKey = "Id", IsForeignKey = true)]

      public Elementi Category
        {
            // setto il get
            get { return _category.Entity; }

            set
            {
                NotifyPropertyChanging("Category");
                _category.Entity = value;
                if (value != null)
                {
                    _categoryId = value.Id;
                }

                NotifyPropertyChanging("Category");
            }
        }