Question

这是我在c＃中创建的Sql函数类。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Sql;
using System.Data.SqlClient;
using System.Data;
using System.Windows.Forms;

namespace DatabaseTest
{
   static class SQLFunctions
{

   static private SqlConnection dbconnect = new SqlConnection(@"Data Source=sourcecode_guy-pc\sqlexpress;Initial Catalog=test;Integrated Security=True");



   static public void Delete(object button) // This is the *Delete Function*
   {
       try
       {
           dbconnect.Open();

           int IsDeleted;

           SqlCommand DeleteAllQuery = new SqlCommand("DELETE FROM users", dbconnect);
           DeleteAllQuery.ExecuteNonQuery();
           IsDeleted = (int)DeleteAllQuery.ExecuteScalar();

           if (IsDeleted == 0)
           {
               MessageBox.Show("Database has been truntcated.");
           }
           else if(IsDeleted == 1)
           {
               MessageBox.Show("An error has occured and your database table was not deleted.");
           }
       }
       catch (Exception ex)
       {
           MessageBox.Show(ex.ToString());
       }
       finally
       {
            dbconnect.Close();
           }
       }

   }
}

这是我表单中的删除按钮

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace DatabaseTest
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnDelete_Click(object sender, EventArgs e)
        {
            SQLFunctions.Delete(button: btnDelete);
        }
    }
}

当我运行程序时，它给了我一个 System.NullReferenceException：对象引用未设置为对象的实例。在中的DatabaseTest.SQLFunctions.Delete（对象按钮） C：\我的路径：）

Answer 1

您的代码执行命令两次。

DeleteAllQuery.ExecuteNonQuery();
IsDeleted = (int)DeleteAllQuery.ExecuteScalar();

删除其中一个。

VS2010截断表的函数

1 个答案: