我的删除功能没有删除条目并且被忽略

Question

我在让我的删除功能在我的 ASP.net (C#) Web 应用程序中工作时遇到问题，我真的不知道下一步该去哪里。

在单击按钮时调用该函数，但好像Page_Load 方法完全忽略了该命令。我是新手，希望能得到一些帮助。 谢谢。

这里是Page_load、DisplayData 方法、Count 方法和通过按钮单击调用的delete 方法。

public partial class WebForm1 : System.Web.UI.Page
{
    SqlConnection cn;
    static int count = 1;
    static int max = 2;
    static String sqlQuery = "Select * from Footballer";
    static bool firstTime = true;

    protected void Page_Load(object sender, EventArgs e)
    {
        string str = "Data Source=(LocalDB)\\MSSQLLocalDB;AttachDbFilename=\"C:\\Users\\David\\Desktop\\WebApplication5\\WebApplication5\\App_Data\\Database2.mdf\";Integrated Security=True";
        cn = new SqlConnection(str);
        SqlCommand command = cn.CreateCommand();

        cn.Open();
        mycount();

        if (firstTime == true)
        {
            displayData();
           firstTime = false;
        }
    }

    protected void mycount()
    {   // count no of els in table
        max = 0;
        var cmd = cn.CreateCommand();

        cmd.CommandText = sqlQuery;
        var reader = cmd.ExecuteReader();
        while (reader.Read()) max++;
        reader.Close();
    }

    protected void displayData()
    {
        var cmd = cn.CreateCommand();

        cmd.CommandText = sqlQuery;
        var reader = cmd.ExecuteReader();

        for (int i = 0; i < count; i++) 
            reader.Read();

        TextBox1.Text = "" + reader[0];
        TextBox2.Text = "" + reader[1];
        TextBox5.Text = "" + reader[2];
        TextBox6.Text = "" + reader[3];
        TextBox7.Text = "" + reader[4];
        TextBox8.Text = "" + reader[5];

        reader.Close();
    }

    protected void deleteData()
    {
        var cmd = cn.CreateCommand();
        string query = "DELETE FROM [Footballer] WHERE [PlayerName] = @name";
        cmd.CommandText = query;

        string name = TextBox4.Text;

        cmd.Parameters.AddWithValue("@name", name);

        cmd.ExecuteNonQuery();
    }
}

Answer 1

从代码中，看起来 Textbox4 值在删除之前被覆盖，Page_load 将在每次回发时调用，包括按钮单击事件。 bool firstTime = true 标志不适用于您要达到的目的。我相信您只想在页面第一次加载时才加载文本框数据。因此您应该修改 Page_load 事件以使用 IsPostBack 属性而不是 firstTime 标志，如下所示。

protected void Page_Load(object sender, EventArgs e)
{
    string str = "Data Source=(LocalDB)\\MSSQLLocalDB;AttachDbFilename=\"C:\\Users\\David\\Desktop\\WebApplication5\\WebApplication5\\App_Data\\Database2.mdf\";Integrated Security=True";
    cn = new SqlConnection(str);
    SqlCommand command = cn.CreateCommand();

    cn.Open();
    mycount();

    if(!IsPostBack)
    {
        displayData();             
    }
}

这将确保您在 UI 中输入的 TextBox4 值在您单击删除按钮时不会被覆盖，并且删除代码应该按预期工作

Answer 2

不要在Page_Load 中打开连接，仅在需要时打开它。也可以使用using 来妥善处理您的资源。

public partial class WebForm1 : System.Web.UI.Page
{
    //You should really pull this from your web.config
    string connectionString = "(LocalDB)\\MSSQLLocalDB;AttachDbFilename=\"C:\\Users\\David\\Desktop\\WebApplication5\\WebApplication5\\App_Data\\Database2.mdf\";Integrated Security=True";;
    static int count = 1;
    static int max = 2;
    static String sqlQuery = "Select * from Footballer";
    static bool firstTime = true;

    protected void Page_Load(object sender, EventArgs e)
    {            
        mycount();

        if (firstTime == true)
        {
            displayData();
           firstTime = false;
        }
    }

    protected void mycount()
    {   // count no of els in table
        max = 0;
        using(SqlConnection con = new SqlConnection(connectionString))
        {
            con.open();
            using(var cmd = cn.CreateCommand())
            {
               cmd.CommandText = sqlQuery;
               var reader = cmd.ExecuteReader();
               while (reader.Read()) max++;
               reader.Close();
            }
        }
    }

    protected void displayData()
    {
        using(SqlConnection con = new SqlConnection(connectionString))
        {
            con.open();
            using(var cmd = cn.CreateCommand())
            {  
               cmd.CommandText = sqlQuery;
               var reader = cmd.ExecuteReader();
               for (int i = 0; i < count; i++) reader.Read();
                 TextBox1.Text = "" + reader[0];
                 TextBox2.Text = "" + reader[1];
                 TextBox5.Text = "" + reader[2];
                 TextBox6.Text = "" + reader[3];
                 TextBox7.Text = "" + reader[4];
                 TextBox8.Text = "" + reader[5];
               reader.Close();
         }
       }
    }

    protected void deleteData()
    {
        //Add A break point here to ensure the method is hit
        using(SqlConnection con = new SqlConnection(connectionString))
        {
            con.open();
            using(var cmd = cn.CreateCommand())
            {            

              string query = "DELETE from [Footballer] where [PlayerName] = @name";
              cmd.CommandText = query;

              string name = TextBox4.Text;    
              //When stepping through in debug mode, make sure
              //name is what you expect.
              cmd.Parameters.AddWithValue("@name", name);

             cmd.ExecuteNonQuery(); 
            }
       }
    }

注意，我已经在 SO 编辑器中完成了所有这些操作，所以我可能错过了一些结束 }