display single/multiple Checkbox selection results in DDL

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VB

ASP.NET

SQL-Server

The idea here is to allow users to set a pre-define search criteria for data retrieval from a MS SQ L Database. A submit button will be added later to search another database that holds the data to be retrieved once completed.
This is not the issue. Please see file/example below.

The Problem
With the file/example below, a:
1. User can select a Supplier of interest from the Supplier/DDL.
2. User will then select a Category of interest from the Categories/Checkboxes.
3. After those selections are made, the Product/DDL will populate/update
based on user’s Supplier/DDL and Categories/Checkboxes selections.
This works OK - if you want the user to select only one item from the Categories/Checkboxes which will populate/update the Product/DDL based on that one item selected.
However, what if a user wants to select more than one Category to see more Products at the same time in the Products/DDL? I would like to see a working model code/solution that will populate/update the Product/DDL
when a user makes multiple Categories selections.
Users should be able to make a single selection from the Supplier/DDL and a single or multiple selections from the Category/Checkboxes.
As such, the Product/DDL should populate/update based on those selections updating selected/un-selected items accordingly. Thank you.

SupplierDDLLoad:
1 Abstract Accent
2 Berma Expo
3 Carter Furniture
4 Dream Inc
5 Elk Design
CategoriesCheckboxes:
1 Bedroom
2 Den
3 Dining
4 Entertainment
5 Kitchen
6 Living
7 Office
8 Patio
ProductDDLLoad?:
Based on Supplier and Category Selections.


Table Items: MS SQ L Database;
This is a sample used only to set pre-define search criteria for user’s data retrieval.

SupID SupplierName CatID CategoryName ProID ProductName SupID CatID
1 Abstract Accent 1 Kitchen 1 Jacobean 1 1
2 Berma Expo 2 Dining 2 American 1 4
3 Carter Furniture 3 Bedroom 3 WilMar 1 2
4 Dream Inc 4 Den 4 Queen A 1 5
5 Elk Designs 5 Living 5 Colonial 1 3
NULL NULL 6 Entertainment 6 Georgian 2 8
7 Office 7 Dutch 2 2
8 Patio 8 Chippendale 2 4
NULL NULL 9 Robert Adam 3 6
10 Hepplewhite 3 4
11 Federal 3 7
12 Sheraton 4 8
13 DunPhyfe 4 5
14 Empire 4 5
15 Shaker 4 6
16 Victorian 4 3
17 ArtsCraft 5 6
18 Art Noveau 5 3
19 Scandinavian 5 4
20 Contemporary 5 7
NULL :) NULL NULL

<asp:CheckBoxList ID="CheckBoxList1" runat="server" AutoPostBack="True"
DataSourceID="SqlDataSource1" DataTextField="CategoryName"
DataValueField="CatID">
    <asp:ListItem>Bedroom</asp:ListItem>
    <asp:ListItem>Den</asp:ListItem>
    <asp:ListItem>Dining</asp:ListItem>
    <asp:ListItem>Entertainment</asp:ListItem>
    <asp:ListItem>Kitchen</asp:ListItem>
    <asp:ListItem>Living</asp:ListItem>
    <asp:ListItem>Office</asp:ListItem>
    <asp:ListItem>Patio</asp:ListItem>
</asp:CheckBoxList>
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
    ConnectionString="<%$ ConnectionStrings:furn %>"
    SelectCommand="SELECT DISTINCT [CatID], [CategoryName] FROM [Category] ORDER BY [CategoryName]">
</asp:SqlDataSource>
</td>
<td class="style2">
<span class="style3"><span class="style4">Product:</span><br />
</span><br />
<asp:DropDownList ID="DropDownList2" runat="server" AutoPostBack="True"
DataSourceID="SqlDataSource3" DataTextField="ProductName"
DataValueField="ProID" onselectedindexchanged="DropDownList2_SelectedIndexChanged">
</asp:DropDownList>
<asp:SqlDataSource ID="SqlDataSource3" runat="server"
    ConnectionString="<%$ ConnectionStrings:furn %>"
    SelectCommand="SELECT DISTINCT [ProID], [ProductName] FROM [Product] WHERE (([SupID] = @SupID) AND ([CatID] = @CatID))"
    onselecting="SqlDataSource3_Selecting">
    <SelectParameters>
        <asp:ControlParameter ControlID="DropDownList1" Name="SupID"
            PropertyName="SelectedValue" Type="Int32" />
        <asp:ControlParameter ControlID="CheckBoxList1" Name="CatID"
            PropertyName="SelectedValue" Type="Int32" />
    </SelectParameters>
</asp:SqlDataSource>