My client wants the ability on the manufacturers view to be able to filter the products by category.

I thought I share what I have done with you in case you need to do something similar.

Open the file TEMPLATE>>MANUFACTURERS>>ProductsInGrid.ascx

Insert a DropdownList


<asp:DropDownList ID="ddlCategories" runat="server" AutoPostBack="True" OnSelectedIndexChanged="ddlCategories_SelectedIndexChanged" DataTextField="Name"      DataValueField="CategoryID" AppendDataBoundItems="true">
</asp:DropDownList>


In the code behind:

Inside the sub FillDropDowns() at the bottom I have populated the ddlCategories dropdown passing the Maufacturer id as a parameter.


            System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["YOURSQLCONNECTION"].ConnectionString);
            System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand("SELECT DISTINCT Nop_Product_Category_Mapping.CategoryID, Nop_Category.Name FROM Nop_Product_Manufacturer_Mapping INNER JOIN Nop_Product_Category_Mapping ON Nop_Product_Manufacturer_Mapping.ProductID = Nop_Product_Category_Mapping.ProductID INNER JOIN Nop_Category ON Nop_Product_Category_Mapping.CategoryID = Nop_Category.CategoryID WHERE (Nop_Product_Manufacturer_Mapping.ManufacturerID = @id)", conn);
            System.Data.SqlClient.SqlDataAdapter da = new System.Data.SqlClient.SqlDataAdapter(cmd);
            System.Data.DataSet ds = new System.Data.DataSet();
            System.Data.DataTable dt = new System.Data.DataTable();
            da.SelectCommand.Parameters.AddWithValue("@id",Convert.ToString(this.ManufacturerId));
            ds.Tables.Add(dt);
            da.Fill(dt);
            ddlCategories.DataSource = dt;
            ddlCategories.DataBind();
            if (ddlCategories.Items.Count <= 1)
            { 
                ddlCategories.Visible = false; 
}
else
{
            ddlCategories.Items.Insert(0, new ListItem("Filter by category", ""));
            ddlCategories.Items.Insert(1, new ListItem("View All", "0")); 
            }

            conn.Close();


Create the sub for the selectedIndexChanged

        
protected void ddlCategories_SelectedIndexChanged(object sender, EventArgs e)
        {
            string url = CommonHelper.GetThisPageUrl(true);
            if (ddlCategories.SelectedItem.Value != "0")
            {
                url = CommonHelper.ModifyQueryString(url, "orderby=" + ddlSorting.SelectedItem.Value + "&categoryid=" + ddlCategories.SelectedItem.Value, null);
            }
            else
            {
                 url = url.Replace(Request.Url.Query, "");
                 url = url.Replace("?orderby=" + Request.QueryString["orderby"] + "&categoryid=" + Request.QueryString["categoryid"], "");
            }
            Response.Redirect(url);
        }



Inside the BinData sub replace the GetAllProducts that populate the productCollection with this


 int categid;

            if (Request.QueryString["categoryid"] != null)
            {
                categid = Convert.ToInt16(Request.QueryString["categoryid"]);
            }
            else
            {
                categid = 0;
            }


            var productCollection = this.ProductService.GetAllProducts(categid,
                    this.ManufacturerId, 0, false, minPriceConverted, maxPriceConverted,
                    string.Empty, false, pageSize, this.CurrentPageIndex,
                    null, orderBy, out totalRecords);



I hope this can be useful for you, if you find a better way of doing the same please let me know.