如何从数据库中删除项目

Question

我有一个GridView，它显示数据库中的项目。当我单击“删除”链接按钮时，我想从数据库中删除项目：

<asp:GridView ID="gvCategories" AutoGenerateColumns="False" runat="server" ItemType="webLicenta.Category"
    SelectMethod="GetCategories" AppendDataBoundItems="true" CssClass="table table-striped table-bordered table-hover">
    <Columns>
        <asp:BoundField DataField="CategoryID" HeaderText="Nr. Categorie" SortExpression="CategoryID" />
        <asp:BoundField DataField="CategoryName" HeaderText="Denumire categorie" SortExpression="CategoryName" />
        <asp:TemplateField HeaderText="Opțiuni">
            <ItemTemplate>
                <asp:LinkButton ID="lnkDeleteCategory" runat="server">Delete</asp:LinkButton>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

我尝试了这个，但没有结果：

protected void gvCategories_SelectedIndexChanged(object sender, EventArgs e)
    {
        using (var _db = new webLicenta.MagazinDBEntities())
        {
            int categoryId = Convert.ToInt16(gvCategories.SelectedValue);
            var myItem = (from c in _db.Categories where c.CategoryID == categoryId select c).FirstOrDefault();
            if (myItem != null)
            {
                _db.Categories.Remove(myItem);
                _db.SaveChanges();

                string pageUrl = Request.Url.AbsoluteUri.Substring(0, Request.Url.AbsoluteUri.Count() - Request.Url.Query.Count());
                Response.Redirect(pageUrl + "?CategoryAction=remove");
            }