从数据库中删除选定的数据表行

Question

I have a datatable in a DataGridView in C#. I filled this table with values obtained from a MySql database. Right now it can successfully retrieves the database table and adds to it once I added any new values to the datatable on WinForm side. This is the code for this purpose:

dbDataset.RowChanged += new DataRowChangeEventHandler(Row_Changed); // dbDataset is my datatable name

and

    private static void Row_Changed(object sender, DataRowChangeEventArgs e)
    {
            // here sda is my MySqlDataAdapter
            try
            {
                MySqlCommandBuilder cmdb = new MySqlCommandBuilder(sda);
                dbDataset.GetChanges();
                dbDataset.GetChanges(DataRowState.Added);
                dbDataset.GetChanges(DataRowState.Deleted);
                dbDataset.GetChanges(DataRowState.Detached);
                dbDataset.GetChanges(DataRowState.Modified);
                dbDataset.GetChanges(DataRowState.Unchanged);                    
                sda.Update(dbDataset);                
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
    }

But now I found that when I want to delete any row from the table, for instance I select a row and press "delete" key, it shows on the screen that it is deleted, but once I reload my WinForm, it still is there. Obviously it didn't delete that selected row from the database. For that, after some search, I added these parts:

dbDataset.RowDeleted += new DataRowChangeEventHandler(Row_Deleted);

and

    private static void Row_Deleted(object sender, DataRowChangeEventArgs e)
    {
        dbDataset.AcceptChanges();
    }

By debugging, I found that when I press "delete" key, it enters the Row_Delete function, then to Row_Changed function, but throws an exception, saying:

Additional information: Concurrency violation: the DeleteCommand affected 0 of the expected 1 records.

I searched to get the current row index of selection, so that I could use DataRow.delete method like:

CurrencyManager xCM = = (CurrencyManager)this.BindingContext[this.dataGridView1.DataSource, this.dataGridView1.DataMember];

and in the Row_Deleted function I added:

DataRowView xDRV = (DataRowView)xCM.Current;
DataRow xDR = ((DataRowView)xCM.Current).Row;
xDR.Delete();

but it gives out null exception, saying the datasource of dataGridView1 cannot be null.

Is there any idea for how to delete the selected row from database? Thanks in advance.

Answer 1

I would use two distinct methods for the updates. One for the Insert/Update and one for the Delete.
When you delete a Row the framework will call the RowDeleted event handler, not the RowChanged.

private static void Row_Changed(object sender, DataRowChangeEventArgs e)
{
    try
    {
        MySqlCommandBuilder cmdb = new MySqlCommandBuilder(sda);
        sda.Update(dbDataset);                
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}

private void Row_Deleted(object sender, DataRowChangeEventArgs e)
{
    try
    {
        SqlCommandBuilder cmdb = new SqlCommandBuilder(da);
        da.Update(dt);                
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
    }
}

You should remove the AcceptChanges call. According to MSDN

When you call AcceptChanges on the DataSet, any DataRow objects still in edit-mode end their edits successfully. The RowState property of each DataRow also changes; Added and Modified rows become Unchanged, and Deleted rows are removed.