c# wpf可编辑字段中的Combox值必须与displaymemberpath不同

我有一个组合框在displaymemberpath ('DescriptionComplete'在下面的代码后面)，这就是我在可编辑字段中得到的，但这只是我想要进入可编辑字段的IdEchantillon…我该怎么做呢?

XAML:

<ComboBox x:Name="cbEchantillon" SelectedValue="{Binding CurrentEchantillon.IdEchantillon}" ItemsSource="{Binding OcEchantillon}" DisplayMemberPath="DescriptionComplete" SelectedValuePath="IdEchantillon" SelectedItem="{Binding CurrentEchantillon}" Text="{Binding IdEchantillon}" IsEditable="True" Width="355" FontSize="14" FontFamily="Courier New" SelectionChanged="cbEchantillon_SelectionChanged"></ComboBox>

背后的代码:

public class Echantillon : ViewModelBase
    {
        private string _IdEchantillon;
        private string _Description;
        private DateTime _dateechan;
        private string _descriptionComplete;
}
    public string IdEchantillon
    {
        get { return _IdEchantillon; }
        set { _IdEchantillon = value; RaisePropertyChanged("IdEchantillon"); }
    }

    public string Description
    {
        get { return _Description; }
        set { _Description = value; RaisePropertyChanged("Description"); }
    }
    public DateTime Dateechan
    {
        get { return _dateechan; }
        set { _dateechan = value; RaisePropertyChanged("Dateechan"); }
    }
    public string DescriptionComplete
    {
        get { return string.Format("{0} {1} {2}", IdEchantillon.PadRight(20), Dateechan.ToShortDateString(), Description); }
        set { _descriptionComplete = value; }
    }
}