Is it possible to have an editable DetailsView for entity objects with subclasses?

问题

Suppose I have two classes, one derived from EntityObject and the other derived from the first:

public class Gizmo : EntityObject { ... }
public class SpecialGizmo : Gizmo { ... }

In the ASP.NET page, the user selects a Gizmo in a list (a GridView) and that Gizmo’s details are then presented in a DetailsView. The goal is for the user to be able to view and edit the details.

Here is the relevant DetailsView and its associated EntityDataSource:

<asp:DetailsView ID="GizmosDetailsView" DataSourceID="dsGizmoDetails"
    AutoGenerateEditButton="True" AutoGenerateInsertButton="True"
    AutoGenerateRows="False" DataKeyNames="GizmoId" runat="server">
    <Fields>
        <asp:BoundField DataField="GizmoId" HeaderText="GizmoId" ReadOnly="True" SortExpression="GizmoId" />
        <asp:BoundField DataField="Description" HeaderText="Description" SortExpression="Description" />
        <!-- ... etc. --->
    </Fields>
</asp:DetailsView>

<asp:EntityDataSource ID="dsGizmoDetails" runat="server" ConnectionString="[...]"
    DefaultContainerName="[...]" EnableFlattening="False" EnableUpdate="True"
    Where="it.[GizmoId] = @GizmoId">
    <WhereParameters>
        <asp:ControlParameter ControlID="gvwGizmos" Name="GizmoId" PropertyName="SelectedValue" Type="Int64" />
    </WhereParameters>
</asp:EntityDataSource>

The above fails with the following exception:

InvalidOperationException: Either CommandText or EntitySetName must be defined.

That’s understandable. However, both options presented break something:

If I add EntitySetName="Gizmo", then only entities of actual type Gizmo are ever presented. If a SpecialGizmo is selected, the DetailsView comes up blank.
If I add a CommandText (or a Select) attribute, then the DetailsView no longer supports updating the data. A working “edit” button (that makes edit UI appear) is there, but then clicking “Update” after making edits simply does nothing.

Is there a proper solution to this dilemma?

回答1:

I solved this using the following hack:

Do specify a CommandText on the data source, which makes the DetailsView unable to update the data automatically, but the update UI is still available.

Set the DetailsView’s OnItemUpdating event to something like this:

protected void GizmoDetailsView_Updating(object sender,
        DetailsViewUpdateEventArgs e)
{
    db.ExecuteStoreCommand(/* use e.Keys["GizmoId"] and e.NewValues */);
    db.SaveChanges();

    // manually set the DetailsView back to read-only mode
    GizmoDetailsView.ChangeMode(DetailsViewMode.ReadOnly);

    // need to cancel the event, as otherwise we get the following exception:
    // InvalidOperationException: Update is disabled for this control.
    e.Cancel = true;
}

Downside of this solution: other controls on the page that rely on the data which is thusly updated, do not refresh until a manual page reload by the user.

来源：https://stackoverflow.com/questions/9080971/is-it-possible-to-have-an-editable-detailsview-for-entity-objects-with-subclasse

标签

ASP.NET

detailsview