Move data from one gridview to another for edit and update

Select Category:  <asp:DropDownList runat="server" ID="category" AutoPostBack="true"
                    SelectMethod="GetCatalogCategories" AppendDataBoundItems="true"
                    DataValueField="CategoryID" DataTextField="CategoryName">
                    <asp:ListItem Value="" Text="-select-"/>
                </asp:DropDownList> </td>
            <td>  </td>
            <td> </td>
        </tr>
        <tr>
          
            <td> <asp:GridView ID="Catalog" runat="server" 
               
                AutoGenerateColumns="False" 
                ItemType="DataAccess.Product"
              
                AllowSorting="false"
                 DataKeyNames="ProductID"
                
              
                SelectMethod="GetCatalog">
   
        <Columns>
            <asp:BoundField DataField="ProductID" HeaderText="ProductID"
                SortExpression="ProductID" />
            <asp:BoundField DataField="ProductName" HeaderText="Product Name"
                SortExpression="ProductName" />
            <asp:BoundField DataField="Description" HeaderText="Description"
                SortExpression="Description" />
           
            <asp:BoundField DataField="CategoryID" HeaderText="CategoryID"
                SortExpression="CategoryID" />
         
            <asp:TemplateField HeaderText="Category">
             
             <ItemTemplate>
                    <%#:Item.Category.CategoryName %>
                </ItemTemplate>


            </asp:TemplateField>
         
               <asp:TemplateField HeaderText="Image">
                    <ItemTemplate>
                 <img src="..Checkout/images/<%#:Item.ImagePath%>"
                                                width="20" height="25" border="1" />
                         </ItemTemplate>
                  
                    </asp:TemplateField>
            <asp:TemplateField HeaderText="Select Products">
                
               <ItemTemplate>
                    <asp:CheckBox ID="CheckBox1" runat="server" />
                </ItemTemplate>
            </asp:TemplateField>
     
     
        </Columns>

List<product> tempIDList = new List<product>();
        protected void Page_Load(object sender, EventArgs e)
        {

        }
        private MeatbyMobileContext _db = new MeatbyMobileContext();
        public IQueryable<category> GetCatalogCategories()
        {

            return _db.Categories;

        }

        public IQueryable<product> GetCatalog([Control]int? category)
        {
            var query = _db.Products.Select(p => p);
            if (category.HasValue)
            {
                query = query.Where(p => p.CategoryID == category.Value);
            
            }
            return query;
        
        }

        protected void Button4_Click(object sender, EventArgs e)
        {
           

        for (int z = 0; z < Catalog.Rows.Count; z++)
        {
           MeatbyMobileContext db = new MeatbyMobileContext();

           
            CheckBox chk =  (CheckBox)Catalog.Rows[z].FindControl("CheckBox1");
            if (chk.Checked)
            {

              int dKey = Convert.ToInt32( Catalog.DataKeys[z].Value);
              
                Product product = (from c in db.Products
                                   where c.ProductID.Equals(dKey)
                                select c).SingleOrDefault();

                 tempIDList.Add(product );
                 



        
            }
        
        }

        GridView2.DataSource = tempIDList;
        GridView2.DataBind();