ASP.Net中如何防止GridView编辑更新时只读列数据丢失？

我在ASP.NET中使用GridView绑定SqlDataSource展示数据库Cart表的内容，仅允许用户编辑Amount列，因此将其余列都设置为ReadOnly="True"。测试时虽能正常编辑指定列，但更新提交后，那些只读列的数据会被替换为NULL写入数据库。尝试过处理RowEditing、RowUpdated、RowUpdating等事件，均未解决问题。

可行解决方案 #

修改SqlDataSource的更新查询语句，将不可修改的字段直接设为表中的原始值，仅保留可编辑的Amount列作为参数传入更新。

原GridView代码

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" CellPadding="4" ForeColor="#333333" GridLines="None"  Align="center" Height="138px" Width="548px" BorderColor="#6600FF" BorderStyle="Ridge" HorizontalAlign="Center" DataKeyNames="Id" DataSourceID="SqlDataSource1" >
    <AlternatingRowStyle BackColor="White" ForeColor="#284775" />
    <Columns>
        <asp:CommandField ShowEditButton="True" />
        <asp:BoundField DataField="Id" HeaderText="Id" InsertVisible="False" ReadOnly="True" SortExpression="Id" Visible="False" />
        <asp:BoundField DataField="PhoneName" HeaderText="PhoneName" SortExpression="PhoneName" ReadOnly="True" />
        <asp:BoundField DataField="Amount" HeaderText="Amount" SortExpression="Amount" />
        <asp:BoundField DataField="Price" HeaderText="Price" SortExpression="Price" ReadOnly="True" />
        <asp:BoundField DataField="TotalPrice" HeaderText="TotalPrice" SortExpression="TotalPrice" ReadOnly="True" />
    </Columns>
    <EditRowStyle BackColor="#999999" />
    <FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
    <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
    <PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />
    <RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
    <SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />
    <SortedAscendingCellStyle BackColor="#E9E7E2" />
    <SortedAscendingHeaderStyle BackColor="#506C8C" />
    <SortedDescendingCellStyle BackColor="#FFFDF8" />
    <SortedDescendingHeaderStyle BackColor="#6F8DAE" />
</asp:GridView>

修改后的SqlDataSource代码

<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="*connection string here*" ProviderName="System.Data.SqlClient" SelectCommand="SELECT * FROM [Cart]" DeleteCommand="DELETE FROM [Cart] WHERE [Id] = @original_Id" InsertCommand="INSERT INTO [Cart] ([PhoneName], [Amount], [Price], [TotalPrice]) VALUES (@PhoneName, @Amount, @Price, @TotalPrice)" OldValuesParameterFormatString="original_{0}" UpdateCommand="UPDATE [Cart] SET [PhoneName] = PhoneName, [Amount] = @Amount, [Price] = Price, [TotalPrice] = TotalPrice WHERE [Id] = @original_Id" DataSourceMode="DataReader">
    <DeleteParameters>
        <asp:Parameter Name="original_Id" Type="Int32" />
    </DeleteParameters>
    <InsertParameters>
        <asp:Parameter Name="PhoneName" Type="String" />
        <asp:Parameter Name="Amount" Type="Int32" />
        <asp:Parameter Name="Price" Type="String" />
        <asp:Parameter Name="TotalPrice" Type="String" />
    </InsertParameters>
    <UpdateParameters>
        <asp:Parameter Name="PhoneName" Type="String" />
        <asp:Parameter Name="Amount" Type="Int32" />
        <asp:Parameter Name="Price" Type="String" />
        <asp:Parameter Name="TotalPrice" Type="String" />
        <asp:Parameter Name="original_Id" Type="Int32" />
    </UpdateParameters>
</asp:SqlDataSource>

原理说明 #

问题根源在于：即使将列设为ReadOnly="True"，SqlDataSource仍会将这些列的空值（编辑模式下只读列无输入控件，参数值为空）传入默认的Update语句，导致更新时覆盖原有数据为NULL。修改UpdateCommand后，只读字段直接引用表自身的字段值，不会被参数的空值覆盖，仅更新需要编辑的Amount列。

内容的提问来源于stack exchange，提问作者Con