Forms Data Controls :: Nested DDL From Second Table In GridView - SQL To Codebehind

First, what I am showing here works fine, and I know how to do this if the nested control comes from the same bound table. I could leave it at that, but I don't like SQL code in my aspx page, and want to move it. I'm keeping it simple here, but I can move it to a data access layer later on..... for now, I want to understand what's going on when the page loads and the nested control is rendered and populated. WHAT I LEARN FROM THIS WILL BENEFIT ME ACROSS THE BOARD - NOT just for this instance!!!

My question is, how to grab the SQL query from the aspx page for the NESTED control and move it to the codebehind. I'd LOVE to also move the Selected Value parameter if possible, but mainly want to get the SQL out of the page. I KNOW HOW TO DO THIS for a GridView or any control, but I DO NOT know how to do it for a NESTED CONTROL from a different table - i.e. WHERE it fires (on GridViewEditing or GridViewUpdating or PageLoad....) so I can put in the SQL where it belongs.... and I'm PRETTY darn SURE this can be done without a 'foreach' loop. For discussion's sake here, imagine

1. DATABASE: simple table with employee_ID, employee_name, employee_city as fields
2. DATABASE: simple table containing all cities (city, cityval)
2. simple GridView that displays these 3 fields in same order ON VIEW
3. Template field for city. On PAGE LOAD, this is a simple label bound to the 'city' field. HOWEVER - On EDIT (with edit button), the field changes to a nested DropDownList that is bound to the 'city' table, NOT to the employee table.

4. Selected value is the current city for employee The PROC you see here in the edit item SQL is actually SELECT * FROM [cities] ORDER BY [city_name]

<asp:GridView ID="grdEmployee" runat="server" AutoGenerateColumns="False"
CssClass="grdE" DataKeyNames="employee_ID"
ShowFooter="True">
<Columns>
<asp:BoundField DataField="employee_ID" HeaderText="ID" ReadOnly="True" />
<asp:TemplateField HeaderText="Employee Name">
<ItemTemplate>
<asp:Label ID="lblEmployeeName" runat="server" Text='<%#Eval("employee_name")%>'></asp:Label>
</ItemTemplate>
<EditItemTemplate>
<asp:TextBox ID="txtEmployeeName" runat="server" Text='<%#Eval("employee_name")%>'></asp:TextBox>
</EditItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="City">
<EditItemTemplate>
<asp:DropDownList ID="cboCity" runat="server"
DataSourceID="SqlDataSource1" DataTextField="city" DataValueField="cityval"
SelectedValue='<%# Bind("employee_city") %>'>
</asp:DropDownList>
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
ConnectionString="Data Source=XXXXXXXXXXXX;Initial Catalog=xxxxxxx;Integrated Security=True"
ProviderName="System.Data.SqlClient"
SelectCommand="QUERY_CITY" SelectCommandType="StoredProcedure"></asp:SqlDataSource>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="lblEmployeeCity" runat="server" Text='<%# Bind("employee_city") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>

ALL I want to do is move the SQL Query in the EDIT template above to the code behind. I just don't know WHERE or WHEN in the code this fires and how to handle it when the table is different from the original GridView table. AND the cboCity.SelectedValue, if possible.