我在 SQL Server 中创建了两个表，它们是:
TblStudent:
Tbl省份:
在 Asp.net 设计表单中:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default4.aspx.cs" Inherits="Default4" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<table>
<tr>
<td>
<asp:Label ID="Label1" runat="server" Text="StudentName"></asp:Label>
</td>
<td>
<asp:TextBox ID="txtStudentName" runat="server"></asp:TextBox>
</td>
</tr>
<tr>
<td>
<asp:Label ID="Label2" runat="server" Text="Province"></asp:Label>
</td>
<td>
<asp:DropDownList ID="ddlProvince" runat="server"></asp:DropDownList>
</td>
</tr>
<tr>
<td colspan="2">
<asp:Button ID="btnSave" runat="server" Text="Save" OnClick="btnSave_Click" />
</td>
</tr>
</table>
</form>
</body>
</html>
在 Asp.net 后端:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
public partial class Default4 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
//bound data from TblProvince to ddlProvince
using (SqlConnection con = DBManager.getConnection())
{
string sql = @"Select ProvinceId, Province From TblProvince";
con.Open();
SqlDataAdapter da = new SqlDataAdapter(sql, con);
DataSet ds = new DataSet();
da.Fill(ds, "dtProvince");
ddlProvince.DataSource = ds.Tables["dtProvince"];
ddlProvince.DataValueField = "ProvinceId";
ddlProvince.DataTextField = "Province";
ddlProvince.DataBind();
ddlProvince.Items.Insert(0, new ListItem("Please Select", "NULL"));
}
}
}
protected void btnSave_Click(object sender, EventArgs e)
{
using (SqlConnection con = DBManager.getConnection())
{
string sql = @"Insert Into TblStudent(Name, ProvinceId) Values(@Name, @ProvinceId)";
SqlCommand cmd = new SqlCommand(sql, con);
cmd.Parameters.Add("@Name", SqlDbType.NChar).Value = txtStudentName.Text;
cmd.Parameters.Add("@ProvinceId", SqlDbType.Int).Value = Convert.ToInt32(ddlProvince.SelectedValue);
con.Open();
cmd.ExecuteNonQuery();
}
}
}
问题:
当我没有在 ddlProvince 中选择时，为什么当你将它保存到数据库时它显示错误 Input string was not in a correct format.
最佳答案
它抛出“输入字符串的格式不正确”错误，因为您正试图将 null 转换为 Int。
cmd.Parameters.Add("@ProvinceId", SqlDbType.Int).Value = Convert.ToInt32(ddlProvince.SelectedValue);
您可以在将 SelectedValue 转换为 Int 之前检查它是否为 null，如下所示。
cmd.Parameters.Add("@ProvinceId", SqlDbType.Int).Value = (ddlProvince.SelectedValue == null) ? null : Convert.ToInt32(ddlProvince.SelectedValue)
关于asp.net - 如何使用asp.net将下拉列表中的空值添加到sql server，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/36146330/