Binding DropDownList SelectedValue to DataValueField for GridView Update - asp.net

Question

Ok guys, so I read this:
How to set SelectedValue of DropDownList in GridView EditTemplate
and I'm having the same issue. However, I don't want to bind the selected value to the displayed text, but instead the values. They are different attributes selected from a SQLDataSource. Here is my DDL code with its SQLDataSource:
<asp:DropDownList ID="FoodCodeDropDownList" runat="server"
DataSourceID="Plant_Carton_Food_List"
DataTextField="Food_Description"
DataValueField="PlantMaterial_FoodID"
SelectedValue='<%# Bind("PlantMaterial_FoodID") %>' >
</asp:DropDownList>
<asp:SqlDataSource ID="Plant_Carton_Food_List" runat="server"
ConnectionString="<%$ ConnectionStrings:OMSConnectionString %>"
SelectCommand="SELECT P.PlantMaterial_FoodID,
M.Material_SAP_Value + ' - ' + MD.SAP_Long_Description AS Food_Description
FROM Plant_Carton_Food AS P
LEFT OUTER JOIN Material_Descriptions AS MD
ON P.PlantMaterial_FoodID = MD.Material_ID
LEFT OUTER JOIN Materials AS M
ON P.PlantMaterial_FoodID = M.Material_ID">
</asp:SqlDataSource>
Here is the (abridged) SQLDataSource of the GridView:
<asp:SqlDataSource ID="Plant_Carton_Table" runat="server"
OldValuesParameterFormatString="old_{0}"
ConnectionString="<%$ ConnectionStrings:DBConnectionString %>"
OnInserting="Plant_Carton_Food_Table_Inserting"
OnInserted="Plant_Carton_Food_Table_Inserted"
InsertCommand="spPlantCartonInsert" InsertCommandType="StoredProcedure"
SelectCommand="spPlantCartonSelect" SelectCommandType="StoredProcedure"
UpdateCommand="spPlantCartonUpdate" UpdateCommandType="StoredProcedure">
<UpdateParameters>
<asp:Parameter Name="Active_Case" Type="Boolean" />
<asp:Parameter Name="PlantMaterial_FoodID" Type="String" />
<asp:Parameter Name="PlantMaterial_CaseID" Type="String" />
...
</UpdateParameters>
...
</asp:SqlDataSource>
And, finally, my exception:
DataBinding: 'System.Data.DataRowView'
does not contain a property with the
name 'PlantMaterial_FoodID'.
I really don't have much knowledge on how databinding through the GridView Edit templates work, but I was able to see that the correct values pass through the OnRowCommand event handler for updates. How do I propagate these values to the SQLDataSource without getting NULL?
Right now, I guess any explanation on how databinding with GridView templates work in general would be beneficial as well. Thanks!

Answer 1

This isn't really an answer to the question, but instead a workaround... but it works for me.
I added PlantMaterial_FoodID as a hidden column into the GridView and changed the SelectedValue binding on the DropDownList to reference this new column, as shown below.
New Column
<asp:TemplateField HeaderText="Food ID" SortExpression="Food_ID">
<EditItemTemplate>
<asp:Label ID="FoodIDLabel" runat="server" Text='<%# Eval("Food_ID") %>'</asp:Label>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="FoodIDLabel" runat="server" Text='<%# Bind("Food_ID") %>'</asp:Label>
</ItemTemplate>
</asp:TemplateField>
...and here is the new binding
<asp:DropDownList ID="FoodCodeDropDownList" runat="server"
DataSourceID="Plant_Carton_Food_List" DataTextField="Food_Description"
DataValueField="PlantMaterial_FoodID" SelectedValue='<%# Bind("Food_ID") %>'
</asp:DropDownList>
This effectively sets the selected dropdownlist index to the correct value.

Answer 2

Have you checked that PlantMaterial_FoodID is spelled exactly as in the SqlDataSource SelectCommand?