更新DataGrid单元仅适用于根对象属性

Question

我有这个实体

public class StockQuantity : EntityBase
{
    public virtual Part Part { get; set; }
    public int Quantity { get; set; }
    public int PartId { get; internal set; }
}

Part

public class Part : EntityBase
{
    public string OEMNumber { get; set; }
    public string BellNumber { get; set; }
    public string Description { get; set; }
    public string CountryOfOrigin { get; set; }
    [Column(TypeName = "decimal(9, 3)")]
    public double Weight { get; set; }

    public virtual StockQuantity StockQuantity { get; set; }
    public virtual ICollection<PartQuantity> PartQuantities { get; set; }

    public virtual CountryCode CountryCode { get; set; }
}

我要绑定到DataGrid

<DataGrid ItemsSource="{Binding StockQuantities}" 
            SelectedItem="{Binding SelectedStockQuantity}"
            x:Name="dataGridConsignments" 
            Margin="10,47,10,9.6"
            ColumnWidth="*" AutoGenerateColumns="False" CanUserAddRows="True">

    <i:Interaction.Triggers>
        <i:EventTrigger EventName="CellEditEnding">
            <i:InvokeCommandAction Command="{Binding UpdateQuantity}"/>
        </i:EventTrigger>
    </i:Interaction.Triggers>

    <DataGrid.Columns>
        <DataGridTextColumn IsReadOnly="True" Header="Bell Number" Width="100" Binding="{Binding Part.BellNumber}"></DataGridTextColumn>
        <DataGridTextColumn IsReadOnly="False" Header="Description" Binding="{Binding Part.Description}"></DataGridTextColumn>
        <DataGridTextColumn IsReadOnly="False" Header="COO" Binding="{Binding Part.CountryCode.Code}"></DataGridTextColumn>

        <DataGridTextColumn IsReadOnly="False" Header="Quantity" Width="100" Binding="{Binding Quantity,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" ></DataGridTextColumn>
    </DataGrid.Columns>
    <DataGrid.InputBindings>
        <MouseBinding Gesture="LeftDoubleClick"  Command="{Binding RowDoubleClick}"/>
    </DataGrid.InputBindings>
</DataGrid>

在我的ViewModel中，我有以下命令，该命令在编辑单元格时会触发：

public ICommand UpdateQuantity
{
    get
    {
        return updateQuantity
            ?? (updateQuantity = new ActionCommand(() =>
            {
                if (SelectedStockQuantity == null)
                    return;
                var stockQ = AllStockQuantities.FirstOrDefault(sq => SelectedStockQuantity.Id == sq.Id);
                if (stockQ == null)
                    return;
                StandardDatabase.Commands.UpdateStockQuantity(stockQ.Part.Id, SelectedStockQuantity.Quantity, SelectedStockQuantity.Part.CountryCode.Code);
            }));
    }

}

问题是，当命令触发时，我可以看到Quantity的更新值（这是StockQuantity的根级属性），但是当我尝试更新CountryCode时或Description，则原始值仍存储在SelectedStockQuantity中，因此不会在数据库中更新。

有人知道我可以在这种情况下强制SelectedStockQuantity更新子对象属性吗？