Linq to sql：增删改

public partial class _Default : System.Web.UI.Page
{
GuestBookDataContext ctx = new GuestBookDataContext("server=xxx;database=GuestBook;uid=xxx;pwd=xxx");
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
SetBind();
}
}
protected void btn_SendMessage_Click(object sender, EventArgs e)
{
tbGuestBook gb = new tbGuestBook();
gb.ID = Guid.NewGuid();
gb.UserName = tb_UserName.Text;
gb.Message = tb_Message.Text;
gb.IsReplied = false;
gb.PostTime = DateTime.Now;
ctx.tbGuestBooks.Add(gb);
ctx.SubmitChanges();
SetBind();
}
private void SetBind()
{
rpt_Message.DataSource = from gb in ctx.tbGuestBooks orderby gb.PostTime descending select gb;
rpt_Message.DataBind();
}
}

<div>
<asp:Repeater ID="rpt_Message" runat="server" OnItemCommand="rpt_Message_ItemCommand">
<ItemTemplate>
<table width="600px" style="border:solid 1px #666666; font-size:10pt; background-color:#f0f0f0">
<tr>
<td align="left" width="400px">
<%# Eval("Message")%>
</td>
<td align="right" width="200px">
<%# Eval("PostTime")%> - <%# Eval("UserName")%>
</td>
</tr>
<tr>
<td colspan="2" align="right">
<hr width="300px" />
<asp:Button ID="btn_DeleteMessage" runat="server" Text="删除留言" CommandName="DeleteMessage" CommandArgument='<%# Eval("ID")%>'/>
管理员回复：<asp:TextBox runat="server" ID="tb_Reply" TextMode="MultiLine" Width="300px" Text='<%# Eval("Reply")%>'/>
<asp:Button ID="btn_SendReply" runat="server" Text="发表回复" CommandName="SendReply" CommandArgument='<%# Eval("ID")%>'/>
</td>
</tr>
</table>
<br/>
</ItemTemplate>
</asp:Repeater>
</div>