Retrieve value of complex object bound to gridview control

Question

The gridview control makes databinding of complex objects rather easy. In my scenario a gridview control gets bound to a Customer object which has a few 'flat' properties and one complex property that takes an object of the type Address. The grid displays the data as expected. The problem is that I have found no way to access the values of the Address properties in code behind. For example, setting the DataKeyNames collection to DataKeyNames="Id, Address.Id" results in an error:

DataBinding: System.Data.Entity.DynamicProxies.Customer_95531162E60920A5C3C02043F6564873913B91785C856624301E8B6E89906BF6 does not contain a property with the name Address.Id.

What is the proper way to access the value of the Address.Id field in code behind? Ideally I'd like to do something like:

    protected void CustomerDetailsObjectDataSource_Selecting(object sender, ObjectDataSourceSelectingEventArgs e)
{
    if (CustomersGridView.SelectedIndex < 0) return;        

    // Retrieving the Customer's id works:
    e.InputParameters["id"] = Convert.ToString(CustomersGridView.DataKeys[CustomersGridView.SelectedIndex].Value);        

    // Retrieving the Address id doesn work:
    e.InputParameters["id"] = Convert.ToString(CustomersGridView.DataKeys[CustomersGridView.SelectedIndex].Values["Address.Id"].ToString());        
}

Here's the asp code:

<ContentTemplate>

        <asp:GridView ID="CustomersGridView" runat="server" AutoGenerateColumns="False" DataSourceID="CustomersObjectDataSource"
                      onselectedindexchanged="CustomersGridView_SelectedIndexChanged" DataKeyNames="Id,Address.Id" ondatabound="CustomersGridView_DataBound">
            <Columns>
                <asp:TemplateField HeaderText="Aktion">
                    <ItemTemplate>
                        <asp:LinkButton runat="server" ID="SelectCustomerButton" Text="Auswählen" CommandName="Select" /> <br/>                         
                    </ItemTemplate>
                </asp:TemplateField>

                <asp:TemplateField HeaderText="Kunde" SortExpression="LastName" ItemStyle-VerticalAlign="Top" >
                    <ItemTemplate>
                        <asp:Label ID="NumberLabel" runat="server" Text='<%#"GpNr: " + Eval("Number")%>'></asp:Label><br/>
                        <asp:Label ID="SalutationLabel" runat="server" Text='<%#Eval("Salutation")%>'></asp:Label>
                        <asp:Label ID="TitleLabel" runat="server" Text='<%#Eval("Title")%>'></asp:Label>
                        <asp:Label ID="FirstNameLabel" runat="server" Text='<%#Eval("FirstName")%>'></asp:Label>
                        <asp:Label ID="LastNameLabel" runat="server" Text='<%#Eval("LastName")%>'></asp:Label><br/>
                        <asp:Label ID="NameContactPersonLabel" runat="server" Text='<%#"Kontakt: " + Eval("NameContactPerson")%>'></asp:Label>
                    </ItemTemplate>
                    <ItemStyle VerticalAlign="Top" />
                </asp:TemplateField>
                <asp:TemplateField HeaderText="Adresse" SortExpression="Address.PostalCode" ItemStyle-VerticalAlign="Top" >
                    <ItemTemplate>                            
                        <asp:Label ID="AddressIdLabel" runat="server" Text = '<%#Eval("Address.Id") %>'></asp:Label>
                        <asp:Label ID="AddressStreetLabel" runat="server" Text='<%#Eval("Address.Street")%>'></asp:Label>
                        <asp:Label ID="AddressHouseNumberLabel" runat="server" Text='<%#Eval("Address.HouseNumber")%>'></asp:Label>
                        <asp:Label ID="AddressHouseNumberExtensionLabel" runat="server" Text='<%#Eval("Address.HouseNumberExtension")%>'></asp:Label>
                        <asp:Label ID="AddressDoorNumberLabel" runat="server" Text='<%#Eval("Address.DoorNumber")%>'></asp:Label><br/>
                        <asp:Label ID="AddressPostalCodeLabel" runat="server" Text='<%#Eval("Address.PostalCode")%>'></asp:Label>
                        <asp:Label ID="AddressCityLabel" runat="server" Text='<%#Eval("Address.City")%>'></asp:Label><br/>
                        <asp:Label ID="AddressCountryLabel" runat="server" Text='<%#Eval("Address.Country")%>'></asp:Label>
                    </ItemTemplate>

Thanks!!

Answer 1

the reason is Gridview consider datakeynames as the property name, it is using DataBinder.GetPropertyValue() during CreateChildControls() to retrieve data key values, while DataBinder.Eval support multiple level property( as long as it is separated by dot character)

Example:

object item = ...
DataBinder.Eval(item, "Address.Id"); //no problem
DataBinder.GetPropertyValue(item, "Address.Id"); //will throw exception

there are several solution to solve your problem:

1. derive your custom gridview(override the CreateChildControls()) that it's datakeynames support multi layer expression. You may refer the default implementation by using Reflector. (lots of work)
2. store the complex property values into viewstate during RowDataBound event (prefered, and also used by me too :) )

Example:

private void CustomersGridView_RowDataBound(object sender, EventArgs args)
{
    if(e.Row.RowType = DataControlRowType.DataRow)
    {
        object id = DataBinder.Eval(e.Row.DataItem, "Id");

        //DictionaryInViewState is a variable that will be stored into viewstate later
        DictionaryInViewState[id] = DataBinder.Eval(e.Row.DataItem, "Address.Id");
    }
}

References:

http://www.telerik.com/forums/problem-with-a-complex-datakeynames-value