I need to delete selected row from the datagridview

Question

I want to delete the selected row in the DataGridView from a database but I get a different index. Any suggestions where I'm doing something wrong?

private void Button3_Click(object sender, EventArgs e)
{
    foreach (DataGridViewCell oneCell in dataGridView1.SelectedCells)
    {
        if (oneCell.Selected)
        {
            dataGridView1.Rows.RemoveAt(oneCell.RowIndex);
            string deleteQuery = $"DELETE FROM {comboBox1.SelectedItem} WHERE id= " + oneCell.RowIndex;
            form1.conn = new SqlConnection($"Server = {form1.ServerBox.Text }; Database = { form1.DBBox.Text}; Trusted_Connection = True");
            form1.cmd = new SqlCommand(deleteQuery, form1.conn);
            form1.conn.Open();
            form1.cmd.ExecuteNonQuery();
            form1.conn.Close();
        }
    }
}

Answer 1

I'm pretty sure the problem lies with your

dataGridView1.Rows.RemoveAt(oneCell.RowIndex);

Here you seem to be deleting the row from the DataGridView . Therefore when you're trying to get the index from the cell with oneCell.RowIndex it is no longer in any row that's part of the DataGridView => RowIndex -1

Try deleting the row from the DataGridView after trying to access the index:

private void Button3_Click(object sender, EventArgs e)
{
    foreach (DataGridViewCell oneCell in dataGridView1.SelectedCells)
    {
        if (oneCell.Selected)
        {
            string deleteQuery = $"DELETE FROM {comboBox1.SelectedItem} WHERE id= " + oneCell.RowIndex;
            form1.conn = new SqlConnection($"Server = {form1.ServerBox.Text }; Database = { form1.DBBox.Text}; Trusted_Connection = True");
            form1.cmd = new SqlCommand(deleteQuery, form1.conn);
            form1.conn.Open();
            form1.cmd.ExecuteNonQuery();
            form1.conn.Close();

            dataGridView1.Rows.RemoveAt(oneCell.RowIndex);
        }
    }
}

Edit:
As others in the comments have already mentioned, it's probably not the best idea to use a RowIndex as an id for a database in the first place.

Answer 2

I think your approach is not correct as you are iterating through selected cells. What happens if you select more than one cells in a row. Will you delete this row twice?

I propose following:

private void Button3_Click(object sender, EventArgs e)
{
    var selectedRows = dataGridView1.SelectedRows.Cast<DataGridViewRow>().ToArray();
    for (int i = 0; i < selectedRows.Length; i++)
    {
        if(selectedRows[i].Cells[idColumn.Index].Value is int id)
        {
            string deleteQuery = $"DELETE FROM {comboBox1.SelectedItem} WHERE id= " + id;
            form1.conn = new SqlConnection($"Server = {form1.ServerBox.Text }; Database = { form1.DBBox.Text}; Trusted_Connection = True");
            form1.cmd = new SqlCommand(deleteQuery, form1.conn);
            form1.conn.Open();
            form1.cmd.ExecuteNonQuery();
            form1.conn.Close();
            dataGridView1.Rows.Remove(selectedRows[i]);
        }
    }
}