Question

我正在制作登录申请。但是当我在我的应用程序中创建一个新用户时，当用户已经存在于数据库中时，我会收到错误。所以我想让我的标签lblOkToe成为用户已经存在的错误消息。

以下是我正在使用的代码：

    private void btnVoegToe_Click(object sender, EventArgs e)
    {
        // Velden leegmaken

        string Wacht = txtWacht.Text;
        string Login = txtLogin.Text;

        //Parameters Declareren
        SqlParameter Para1 = new SqlParameter();
        SqlParameter Para2 = new SqlParameter();
        Para1.ParameterName = "@Log";
        Para2.ParameterName = "@WW";
        Para1.Value = Login;
        Para2.Value = Wacht;


        // SQL Connectie opzetten
        SqlConnection Conn = new SqlConnection();
        Conn.ConnectionString = @"Integrated Security=true;Initial Catalog=Wachtwoord;Data Source=LAPTOP-PDI9B3LP\SCHOOL";
        Conn.Open();

        SqlCommand cmd = new SqlCommand();
        cmd.Connection = Conn;

        // Alles selecteren van tabel Favorieten
        cmd.CommandText = "insert into gebruik values (@Log, @WW)";

        //Koppelen van SqlParameter met SqlCommand
        cmd.Parameters.Add(Para1);
        cmd.Parameters.Add(Para2);

        int gelukt = cmd.ExecuteNonQuery();

        if (gelukt == 1 && )
        {
            lblOKToe.Text = "De gebruiker" + Login + " is toegevoegd";
            cbKeuze.Items.Add(Login);
            txtLogin.Text = "";
            txtWacht.Text = "";
        }
        // Database connectie sluiten
        Conn.Close();
    }

Answer 1

取决于dB的返回结果：

int gelukt = cmd.ExecuteNonQuery();

如果gelukt为1，则“受影响的记录”为1，并且“记录”已成功插入。

如果gelukt为0则SQL INSERT失败。很可能是因为你有独特的限制或类似的东西。

所以代码是：

if (gelukt == 1) 
  { 
   lblOKToe.Text = "De gebruiker" + Login + " is toegevoegd"; 
   cbKeuze.Items.Add(Login); 
   txtLogin.Text = ""; 
   txtWacht.Text = ""; 
  }
else //if (gelukt == 0)
  {
    lblOKToe.Text = "Failed to register, use another name.";
  }

C＃检查数据库中是否已存在记录

1 个答案: