JS制作的简单的三级及联

<form id="form1" runat="server">
<div>
省
<select id="Province">
<option>请选择</option>
</select>
市
<select id="City">
<option>请选择</option>
</select>
地区
<select id="Space">
<option>请选择</option>
</select>
<script type="text/javascript">
$(function () {
$.ajax({
url: "TestClass/Cascade.ashx?id=1",
async: false,
success: function (data) {
$("#Province").append(data);
$("#Province").change(function () {
$.ajax({
url: "TestClass/Cascade.ashx?id=2",
data: { pid: $("#Province").attr("value") },
success: function (data) {
$("#City").html("");
$("#City").append(data);
$("#City").change(
function () {
$.ajax({
url: "TestClass/Cascade.ashx?id=3",
data: { cid: $("#City").attr("value") },
success: function (data) {
$("#Space").html("");
$("#Space").append(data);
}
})
})
}
})
})
}
})
})
</script>
</div>
</form>

public void ProcessRequest(HttpContext context)
{
context.Response.ContentType = "text/plain";
if (context.Request.QueryString["id"] == "")
{
string sql = "SELECT ID,[enname] FROM [ProvinceInfo] WHERE ParentId=0";
StringBuilder sb = new StringBuilder();
SqlDataReader reader = PubSqlHelperFunc.ExecuteSqlDataReader(CommandType.Text, sql, null);
while (reader.Read())
{
sb.Append("<option value=");
sb.Append(reader["Id"]);
sb.Append(">");
sb.Append(reader["enname"]);
sb.Append("</option>");
}
reader.Close();
context.Response.Write(sb.ToString());
}
else if (context.Request.QueryString["id"] == "")
{
string sql = "SELECT ID,[enname] FROM [ProvinceInfo] WHERE ParentId=" + context.Request.Params["pid"] + "";
StringBuilder sb = new StringBuilder();
sb.Append("<option>请选择</option>");
SqlDataReader reader = PubSqlHelperFunc.ExecuteSqlDataReader(CommandType.Text, sql, null);
while (reader.Read())
{
sb.Append("<option value=");
sb.Append(reader["Id"]);
sb.Append(">");
sb.Append(reader["enname"]);
sb.Append("</option>");
}
reader.Close();
context.Response.Write(sb.ToString());
}
else if (context.Request.QueryString["id"] == "")
{
string sql = "SELECT ID,[enname] FROM [ProvinceInfo] WHERE ParentId=" + context.Request.Params["cid"] + "";
StringBuilder sb = new StringBuilder();
sb.Append("<option>请选择</option>");
SqlDataReader reader = PubSqlHelperFunc.ExecuteSqlDataReader(CommandType.Text, sql, null);
while (reader.Read())
{
sb.Append("<option value=");
sb.Append(reader["Id"]);
sb.Append(">");
sb.Append(reader["enname"]);
sb.Append("</option>");
}
reader.Close();
context.Response.Write(sb.ToString());
}
}