如何从SQL Server数据库中删除表行？

Question

I'm having trouble trying to delete rows.

All rows are selected and displayed on a ListBox control.
Then, when calling the btnObrisi_Click event (Obrisi = delete), the selected item from the ListBox will be deleted.

The item is actually removed from the control, but the value is not deleted from the database.

This is the code I'm using:

private string conString = @"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\Database1.mdf;Integrated Security=True;User Instance=True";
private SqlConnection con;
private SqlCommand com;
private DataTable dt;
private SqlDataAdapter da;

private DataTable SelectAll()
{
    con = new SqlConnection(conString);
    com = new SqlCommand();
    dt = new DataTable();
    da = new SqlDataAdapter();

    com.Connection = con;
    com.CommandType = CommandType.Text;
    com.CommandText = "SELECT * FROM predmeti";
    da.SelectCommand = com;
    da.Fill(dt);

    return dt;
}

private void Obrisi(int id)
{
    con = new SqlConnection(conString);
    com = new SqlCommand();
    com.Connection = con;
    com.CommandType = CommandType.Text;
    com.CommandText = "DELETE FROM predmeti WHERE predmetID = @predmetID";
    com.Parameters.AddWithValue("@predmetID", id);

    try
    {
        con.Open();
        com.ExecuteNonQuery();
         MessageBox.Show("Obrisano");
    }
    catch(Exception ex)
    {
         MessageBox.Show(ex.Message);
    }
    finally
    {
         con.Close();
    }
}

private void Citaj()
{
    listBox1.ValueMember = "predmetID";
    listBox1.DisplayMember = "ime_predmeta";
    listBox1.DataSource = SelectAll();
}

private void btnOsvezi_Click(object sender, EventArgs e)
{
    Citaj();
}

private void Form1_Load(object sender, EventArgs e)
{
    Citaj();
}

private void btnObrisi_Click(object sender, EventArgs e)
{
    int id = Convert.ToInt32(listBox1.SelectedValue);
    Obrisi(id);
    Citaj();
}

Answer 1

When you have a database file in your project and then you build the project, the database file could be copied from the root project folder into the output (bin\\debug or bin\\release) folder.
This behavior is controlled by the Copy To Output Directory property on the database file.

If you have this property set to Copy Always then, every time you build your project a fresh copy of the database file is copied from the root project folder to the output directory overwriting the one already there and destroying the changes you have made in the previous debug session.

A suggested fix is to change this property to Copy Never or Copy if Newer

See a detailed explanation on MSDN at this page

The shortcut |DataDirectory| in the connection string points (for a winforms project) to the bin\\debug or bin\\release relative subfolder of the current project, Any changes made by your program works on the database located there, but these changes are overwritten at the next run