单击按钮时从 Access 数据库中删除特定记录

Question

我有一个包含 9 个字符的字符串，例如 LON052012（来自伦敦 23.05.2012.-day.month.year.）。我想从 Access 中的表中删除所有记录，其中所有城市都以该字符串中的前三个字母开头并具有这些月份和年份 (05.2007.)。

这是函数：

private void button2_Click(object sender, EventArgs e)
    {
        if (textBox1.Text != "")
        {
            try
            {
                string sTown, s1, s2;
                sTown = textBox1.Text.Substring(0, 3);
                s1 = textBox1.Text.Substring(3, 2);
                s2 = textBox1.Text.Substring(5);

                string sDelete = "DELETE * FROM Country WHERE Town LIKE @p1 and month(TownDate) = @p2 and year(TownDate) = @p3";
                OleDbCommand komDelete = new OleDbCommand(sDelete, connection);
                komDelete.Parameters.AddWithValue("@p1", sTown + "*");
                komDelete.Parameters.AddWithValue("@p2", s1);
                komDelete.Parameters.AddWithValue("@p3", s2);
                connection.Open();
                komDelete.ExecuteNonQuery();
                MessageBox.Show("Deleted");
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
            finally
            {
                connection.Close();
            }
        }
        else
        {
            MessageBox.Show("TextBox is empty!");
        }
    }

这是表格 Country 的样子（CountryID、Town、TownDate）：

它总是说记录被删除，即使没有。

Answer 1

试试这个：

        if (textBox1.Text != "")
    {
        //retrieve data
        string sTown, sMonth, sYear;
        sTown = textBox1.Text.Substring(0, 3);
        sMonth = textBox1.Text.Substring(3, 2);
        sYear = textBox1.Text.Substring(5);

        //validate input
        bool valid_town = new Regex(@"[a-z]", RegexOptions.IgnoreCase).IsMatch(sTown) && new Regex(@"[^0-9]").IsMatch(sTown) && sTown.Length ==3;
        bool valid_month = new Regex(@"[0][1-9]|[1][0-2]").IsMatch(sMonth) && new Regex(@"[^a-z]", RegexOptions.IgnoreCase).IsMatch(sMonth) && sMonth.Length ==2;

        int year = 0;
        bool isNum = int.TryParse(sYear,out year);
        bool valid_year = new Regex(@"[^a-z]", RegexOptions.IgnoreCase).IsMatch(sYear) && sYear.Length == 4 && (isNum ? year > 1980 && year < 2100 : false);



        string newLine = System.Environment.NewLine;

        //if input valid
        if (valid_town && valid_month && valid_year)
        {
            //create sql statements
            string sWhere = String.Format("WHERE Town LIKE {0} and month(TownDate) = {1] and year(TownDate) = {2}", sTown,sMonth,sYear);
            string sCount = String.Format("SELECT COUNT(*) FROM Country {0}", sWhere);
            string sDelete = String.Format("DELETE * FROM Country {0}",sWhere);

            //counts; to be deleted, actually deleted
            int initialCount = 0;
            int deletedCount = 0;

            try
            {
                //create connection//NOTE: Using 'Use' statement will handle opening and closing. I dont know where you created your initial 'connection' object but it could cause you problems by haven a connection that is being used in multiple methods.
                using (OleDbCommand connection = new OleDbCommand(ConnectionString))
                {
                    //get total rows to be affected
                    connection.CommandText = sCount;
                    initialCount = connection.ExecuteNonQuery();

                    //delete rows and get delete count
                    connection.CommandText = sDelete;
                    deletedCount = connection.ExecuteNonQuery();
                    //display message
                    MessageBox.Show(String.Format("Found {0} rows to delete. {1}Deleted {2} rows.", initialCount, newLine, deletedCount));

                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
            finally
            {
                connection.Close();
            }
        }
        {
            //else; input not valid
            MessageBox.Show(String.Format("Failed validation of TextBox:{0}Country:{1}{2}Month{3}{4}Year{5}.", newLine, valid_town.ToString(), newLine, valid_month.ToString(), newLine, valid_year.ToString())); ;

        }
    }
    else
    {
        MessageBox.Show("TextBox is empty!");
    }

您需要使用以下方法添加：

using System.Text.RegularExpressions;

我没有机会创建示例项目来亲自尝试...

Answer 2

对于 UPDATE、INSERT 和 DELETE 语句，ExecuteNonQuery 的返回值是受命令影响的行数。

所以，修改你的代码为：

  var n= komDelete.ExecuteNonQuery();
  if (n >0 )
   {
            MessageBox.Show("Deleted");
   }

编辑

查询中的问题是：

• 参数数据类型 s1 ， s2 它们是字符串，它们 应该作为整数传递。
• 使用 * 应该是 %（访问使用 %，见我的评论）

所以，你必须将代码修改为：

        var p1 = sTown + "%"; // not *
        komDelete.Parameters.AddWithValue("@p1", p1);
        var p2 = int.Parse(s1); //convert to numeric data type
        var p3 = int.Parse(s2);
        komDelete.Parameters.AddWithValue("@p2", p2);
        komDelete.Parameters.AddWithValue("@p3", p3);


      var n= komDelete.ExecuteNonQuery();
     if (n >0 )
     {
            MessageBox.Show("Deleted");
     }

我使用 access 2007 and 2007 Office System Driver: Data Connectivity Components 测试了该代码，它工作正常并删除了该行。